What does
that mean?

The number of times the air inside a room or building is replaced in one hour. It is used when looking at ventilation, air quality and heat loss.

Also called: ACH

In more detail

This compares airflow with the size of the space. It can describe intentional ventilation or leakage measured under test conditions; the test conditions must be stated before comparing figures.

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A measure of how much air leaks through the gaps and cracks in a building. Lower air permeability usually means a more airtight home.

In more detail

Usually expressed as cubic metres of air leaking per hour per square metre of building envelope at a stated pressure. A lower test result means fewer unintended leaks, but says nothing by itself about adequate fresh-air provision.

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A low-carbon heating system that takes heat from the outside air and upgrades it to heat the home and hot water.

Also called: ASHP

In more detail

Uses electricity to move heat from outdoor air into the home, even when the air feels cold. Air-to-water systems serve radiators or underfloor heating; air-to-air systems blow warmed air indoors. Good sizing and controls matter.

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How well a building prevents uncontrolled draughts and air leakage. Good airtightness helps reduce heat loss but must be balanced with suitable ventilation.

Also called: Airtightness

In more detail

Describes control of unintended air movement through the building fabric. It differs from ventilation, which deliberately supplies and removes air. Sealing leaks should therefore be planned alongside extraction and fresh-air provision.

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A pressure test used to measure how leaky a building is. A fan is usually fitted into a doorway to pressurise or depressurise the property.

Also called: Airtightness Test

In more detail

A specialist temporarily fits a fan and measures airflow at controlled pressure differences. Results help locate leakage and quantify it. This is not the same as measuring normal day-to-day ventilation with windows and fans in use.

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The surrounding air temperature. In heating, this often means the outside air temperature.

In more detail

Means the temperature of the air surrounding the item being discussed. Always check whether a specification means outdoor air, room air or a plant-room temperature; this changes how equipment performance should be interpreted.

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A safety check to identify materials that may contain asbestos before retrofit works are carried out.

In more detail

The type and extent of survey should suit the proposed work. Materials cannot reliably be cleared by appearance alone. Suspected asbestos should be assessed by a competent professional before drilling, cutting or removal; homeowners should not take samples themselves.

Further reading: HSE: asbestos surveys. Check current guidance for schemes and standards.

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A detailed inspection of a property to understand its current condition, energy performance, heating systems, insulation, ventilation and retrofit suitability.

In more detail

Brings evidence together rather than simply recommending products. Its scope should be clear: an EPC assessment, condition survey and retrofit assessment answer different questions. Ask what was inspected, what could not be inspected and what further investigation is needed.

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An allowance in a solar-output model for specified real-world system losses, such as wiring and inverter conversion losses.

Also called: PVGIS

In more detail

PVGIS is a solar-output estimation tool. Its system-loss input allows for losses such as wiring, inverter conversion, dirt and mismatch. It is an assumption used in a model, not a guarantee or a replacement for checking shading and installation details.

Further reading: European Commission: PVGIS system losses. Check current guidance for schemes and standards.

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Low-level ventilation, usually through trickle vents or wall vents, that helps provide fresh air and manage moisture.

In more detail

Provides a continuing route for outdoor air to enter occupied rooms. It is normally used with extraction from kitchens and bathrooms, and air-transfer paths between rooms. The required arrangement depends on the ventilation system.

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A boiler flue system that takes air from outside for combustion and removes exhaust gases safely.

In more detail

Often uses concentric pipes, with combustion air entering around the exhaust route. It serves the appliance, not room ventilation. Terminal clearances and installation requirements must be checked by the appropriately qualified installer.

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A system that stores electricity, often from solar panels, so it can be used later in the home.

In more detail

Stores electricity after conversion and releases it when needed. Usable capacity in kWh, maximum charging/discharging power in kW, efficiency and warranty are different specifications. A normal grid-connected battery does not automatically provide backup power during a power cut.

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A heating system that burns organic material, such as wood pellets or logs, to provide space heating and hot water.

In more detail

Burns fuel such as logs, pellets or wood chips and needs suitable fuel storage, maintenance and a compliant flue. Renewable fuel does not mean zero local pollution or automatically low running costs; suitability depends on the property and supply chain.

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A heating appliance that heats water for radiators, underfloor heating or hot water cylinders. Common types include gas, oil, LPG and electric boilers.

In more detail

Transfers heat into water. Fuel-burning boilers and direct electric boilers obtain that heat differently, and their efficiency and emissions differ. Boiler output, heating demand and hot-water requirements should be assessed together rather than selecting a larger unit by default.

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A government grant scheme that can help with the cost of installing eligible low-carbon heating systems such as heat pumps.

Also called: BUS

In more detail

Supports eligible low-carbon heating installations in England and Wales. Eligibility, technology rules and grant amounts can change, so check the current official scheme guidance before relying on a quotation. An application or advertised grant does not guarantee that every project qualifies.

Further reading: Government: Boiler Upgrade Scheme. Check current guidance for schemes and standards.

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An informal term describing how a material or construction manages moisture; it is not the same as allowing air to leak through.

In more detail

An informal description of moisture movement, not a single product rating. Vapour diffusion, liquid-water transport and drying ability are different properties. A wall's finishes and complete build-up matter as much as one material labelled breathable.

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A membrane used in walls or roofs that helps protect against water while allowing water vapour to escape.

In more detail

Resists wind-driven rain while allowing a specified degree of water-vapour passage. It is not interchangeable with a vapour-control layer. Laps, penetrations, support and ventilation spaces must follow the complete roof or wall design.

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A route that bypasses a protective layer, such as insulation or a damp-proof barrier. Its meaning depends on the context.

In more detail

Has different meanings in different contexts. A thermal bridge provides an easier route for heat flow; a damp-proof-course bridge allows moisture to bypass a barrier. The report should say which is meant and identify the actual detail.

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The physical parts of a building that separate the inside from the outside, including walls, floors, roofs, windows and doors.

In more detail

Includes the construction and its junctions rather than the heating equipment. Insulation, weather resistance, airtightness and moisture behaviour all depend on how these parts work together. A good fabric assessment also looks for defects before covering them.

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A wall with two leaves, usually brick or blockwork, separated by a gap or cavity.

In more detail

Usually has an outer weather-facing leaf and an inner structural leaf separated by a gap. The cavity may be empty, partly insulated or filled. Suitability for extra insulation depends on construction, condition and exposure, not just the existence of a gap.

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The removal of failed, unsuitable or wet cavity wall insulation from a property.

In more detail

A remedial process that should follow an investigation showing why removal is needed. Extraction alone may not repair defective gutters, pointing or other sources of water. The removal method and post-work checks should suit the insulation and wall.

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Insulation installed into the cavity between the inner and outer leaves of a wall to reduce heat loss.

Also called: CWI

In more detail

Reduces heat transfer across an appropriate cavity. The insulation type and installation method must match the wall, cavity width and exposure. Surveying for defects and checking installation quality are essential; not every cavity should be filled.

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Insulation made from recycled paper fibres. It is often used in lofts, timber frames and some breathable construction systems.

In more detail

Usually consists of treated recycled paper fibres, installed loose, blown or densely packed depending on the application. Density, settlement, moisture control and fire performance must be considered as part of the specified system.

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A heating system where heat is generated in one place, such as a boiler or heat pump, and distributed around the home.

In more detail

Describes heat distributed from a common source to several rooms. A wet system circulates heated water through pipes; controls and hydraulic balancing influence comfort. The heat source may change without every radiator or pipe necessarily needing replacement.

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A measure of heat pump efficiency at a particular moment. A CoP of 3 means the heat pump is producing three units of heat for every one unit of electricity used.

Also called: CoP

In more detail

Compares useful heat output with electrical input at stated operating conditions. It is a ratio, not a fixed promise for the whole year. Outdoor temperature, water temperature and what equipment is included in the measurement affect the result.

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Another term for a thermal bridge. It is an area where heat escapes more easily, often causing cold spots or condensation risk.

In more detail

A common alternative name for a thermal bridge. The area can feel colder inside because heat flows through it more readily. That lower surface temperature may increase condensation risk, even when no water is entering from outside.

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A boiler that provides heating and hot water directly, without needing a separate hot water cylinder.

In more detail

Heats incoming mains water when a hot tap runs, rather than storing it in a separate cylinder. Hot-water flow depends on appliance output and incoming water conditions. Space-heating and hot-water performance are separate design considerations.

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Ventilation required for appliances that burn fuel, such as gas, oil, LPG, coal or wood.

In more detail

Supplies air needed for safe fuel burning where the appliance design requires it. It must not be removed during draught-proofing or insulation work. Requirements depend on the appliance, flue and installation; a competent specialist should assess changes.

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The process of checking, setting up and recording that a system has been installed correctly and is working as designed.

In more detail

Confirms that installed equipment performs as intended, with settings and measurements recorded. Turning it on is only one part of the process. Handover should include operating instructions, maintenance needs and evidence of the checks completed.

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Heating controls that adjust flow temperature depending on internal or external conditions.

In more detail

Adjust the heating water temperature as conditions change, rather than always running at one high setting. Weather compensation uses outdoor conditions; load compensation responds to indoor demand. The controller and heat source must be compatible and set up correctly.

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Water droplets that form when warm moist air meets a cold surface. It is common on windows, cold walls and areas with poor ventilation.

In more detail

Forms when a surface is cold enough for water vapour in nearby air to turn to liquid. The surface temperature and amount of moisture both matter. Persistent problems require checking moisture sources, ventilation, heating and cold surfaces together.

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In a heat pump or refrigeration cycle, the condenser is the heat exchanger where the refrigerant releases heat into the heating system.

In more detail

The part of a heat pump's refrigerant circuit where heat is released as refrigerant condenses. In an air-to-water heating system, that heat is normally transferred into circulating water. It should not be confused with a condensing boiler.

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An area with special architectural or historic interest. Some retrofit measures may need extra care or permissions.

In more detail

Protects the character of an area rather than only individual buildings. Some external changes may be controlled, and local restrictions vary. Check the relevant planning authority before assuming that a measure is permitted without an application.

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The timers, thermostats, programmers, smart controls and sensors that manage heating, hot water and ventilation systems.

In more detail

Manage when systems run and the conditions they maintain. Good controls need sensible positioning, suitable settings and clear instructions. More features do not automatically mean lower bills; compatibility and how the household uses them matter.

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Unwanted moisture in a building. Common types include penetrating damp, rising damp, condensation-related damp and trapped moisture.

In more detail

A description of excess moisture, not a diagnosis. Water may come from rain, plumbing, ground moisture or condensation, and several causes can overlap. The pattern, timing, construction and measurements should be assessed before selecting treatment.

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A physical or chemical barrier designed to stop moisture rising through walls.

Also called: DPC

In more detail

A layer intended to limit moisture moving upwards through a wall. It may be a physical material or a suitable remedial treatment. Raised soil, debris or other details can bypass it; a low damp patch alone does not demonstrate failure.

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The process of reducing carbon emissions, often by improving insulation, reducing energy demand and switching to low-carbon heating.

In more detail

Means reducing greenhouse-gas emissions associated with an activity. In housing, changes to energy demand, heat sources and electricity supply all affect the result. Operational emissions and emissions from making building materials are different parts of the overall picture.

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The water temperature a heating system is designed to send to radiators or underfloor heating. Lower flow temperatures are usually better for heat pump efficiency.

In more detail

The chosen supply-water temperature at the system's design conditions, usually a cold outdoor temperature. It must work with room heat losses, emitter sizes and water flow. It is not necessarily the temperature used on every day of the year.

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The amount of heat a property or room is expected to lose during cold weather. It is used to size heating systems correctly.

In more detail

Estimates the heat needed to maintain chosen indoor temperatures at specified cold outdoor conditions. It helps select equipment capacity. It is a power figure, normally in kW, rather than an annual energy-use estimate.

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The temperature at which water vapour turns into liquid water. It is important when assessing condensation risk.

In more detail

The temperature at which air with a given moisture content becomes saturated. A surface below that temperature can collect condensation. Changing the room humidity changes the dew point, so there is no single dew-point temperature for every home.

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Heating that uses electricity directly, such as panel heaters, storage heaters, electric radiators or infrared panels.

In more detail

Turns electricity into heat at the point of use, rather than moving heat from outdoors as a heat pump does. Purchase price, tariff, controls and heat demand influence running costs. Efficient conversion alone does not guarantee cheap heating.

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A system where heat is produced centrally and supplied to multiple homes or buildings through a heat network.

In more detail

A type of heat network serving a district or collection of buildings. Heat arrives through insulated pipes and is usually transferred into each property through an interface unit. Charges, metering and heat-source emissions depend on the particular network.

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A qualified person who produces Energy Performance Certificates for existing homes.

Also called: DEA

In more detail

An assessor working with an approved accreditation scheme to produce EPCs for existing dwellings. The role follows a defined assessment method and evidence rules. An EPC visit is not automatically a full building-condition or damp survey.

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Hot water used for taps, baths and showers.

Also called: DHW

In more detail

Water used for washing, bathing and other hot taps, as distinct from the water circulating inside a radiator circuit. Storage temperatures, hygiene controls and safe delivery temperatures are design matters for a competent installer.

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Sealing unwanted gaps around windows, doors, floors and service penetrations to reduce cold draughts and heat loss.

In more detail

Targets unintended air leakage around joints and openings. It should preserve required ventilation, combustion air and drainage routes. The correct seal must suit the location and allow intended movement or operation of the component.

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The fourth phase of the Energy Company Obligation, a government energy-efficiency scheme aimed at improving eligible homes.

In more detail

An energy-supplier obligation supporting eligible domestic energy-efficiency work in Great Britain, with Ofgem administering the scheme. It is not an automatic entitlement to a free installation. Current deadlines, funding availability and household/property eligibility must be checked before committing.

Further reading: Ofgem: current ECO guidance. Check current guidance for schemes and standards.

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A device that gives heat into a room, such as a radiator, underfloor heating loop, fan coil or convector.

In more detail

Transfers heat from the system into a room. Its output depends on size, design, water and air temperatures, and sometimes a fan. A radiator's catalogue output may be quoted at hotter conditions than a heat-pump system will use.

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The process of checking whether radiators or underfloor heating can deliver enough heat at the chosen flow temperature.

In more detail

Matches each room's heat requirement to an emitter at the proposed operating temperatures. Pipework and available flow also matter. Checking only the radiator's physical dimensions or its output at boiler conditions can be misleading.

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Using less energy to achieve the same result, such as heating a home to a comfortable temperature with lower energy use.

In more detail

Compares the useful service obtained with the energy used. A lower-energy home should still provide adequate warmth, fresh air and hot water. Efficiency, total consumption, energy price and carbon emissions are related but are not the same measurement.

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A certificate that rates a property’s energy performance from A to G and gives recommendations for improvement.

Also called: EPC

In more detail

Provides a standardised assessment and improvement recommendations using recorded building data and prescribed assumptions. It is not calculated from the household's actual bills and is not a guarantee of running costs. Check the date and underlying descriptions before relying on it.

Further reading: Government: domestic EPCs. Check current guidance for schemes and standards.

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A retrofit improvement designed to reduce energy use, such as insulation, heating controls, glazing or low-carbon heating.

Also called: ESM

In more detail

An individual improvement intended to reduce energy use. Suitability depends on the building and its other systems. A measure can affect ventilation, moisture and future work, so its place in a whole-house plan matters.

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In a heat pump or refrigeration cycle, the expansion valve reduces the refrigerant pressure and temperature before it enters the evaporator.

In more detail

Controls refrigerant entering the low-pressure side of the cycle. The pressure drop enables evaporation at a low temperature. This is a specialist refrigerant component, not a homeowner heating-water adjustment valve.

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A vessel in a sealed heating system that absorbs expansion as water heats up.

In more detail

Contains a compressible gas cushion separated from water, usually by a diaphragm. It accommodates water expanding as it heats. Pressure problems need proper diagnosis; repeatedly topping up a system is not a repair for a failed vessel or leak.

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Insulation fixed to the outside of external walls and finished with render, cladding or another weatherproof layer.

Also called: EWI

In more detail

Wraps the outside of a wall with insulation and a protective finish. Eaves, window reveals, services, ground levels and water shedding require careful detailing. The existing wall's condition and moisture behaviour must be understood before it is covered.

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A fan that removes moist or stale air from rooms such as bathrooms, kitchens and utility rooms.

In more detail

Removes indoor air through ducting to outdoors or an appropriate extract system. A fan making a noise does not prove adequate airflow. Duct size, bends, grilles, replacement air and maintenance can all influence actual performance.

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Fluorinated greenhouse gas used in some refrigeration, air conditioning and heat pump systems. Some F-gases have high global warming potential.

In more detail

A family of fluorinated gases, including some refrigerants, rather than one specific substance. Environmental impact and rules depend on the gas and equipment. Installation, servicing and disposal should be handled by appropriately qualified people under the applicable requirements.

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Planning improvements to the building fabric and ventilation alongside heating, to reduce avoidable heat demand and support a suitable system design.

In more detail

Prioritises reducing avoidable heat loss and addressing the building's condition before final equipment sizing. It is a planning principle, not a rule that every insulation measure must happen before a heating replacement. Ventilation and moisture need consideration throughout.

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A heat emitter that uses a fan to move air across a heating or cooling coil.

In more detail

Uses a fan to move room air over a heat-exchange coil. Fan speed, water temperature, noise and airflow affect output and comfort. A recirculating fan coil does not necessarily supply outdoor ventilation air.

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Insulation added to a flat roof. It may be installed above, below or within the roof structure depending on the roof type.

In more detail

The insulation position determines whether the roof is described as warm, cold or another build-up. Condensation control, drainage and waterproofing must be designed together. Adding insulation underneath an existing roof without checking the build-up can create moisture risks.

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Insulation added to solid floors, suspended timber floors or between floor joists to reduce heat loss.

In more detail

Reduces heat transfer through the lowest exposed floor or a floor over an unheated space. Solid and suspended floors need different methods. Ground moisture, ventilation, services, thresholds and finished floor levels can limit the options.

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The amount of water moving through a heating system over a set time.

In more detail

Describes the volume or mass of water moving in a given time, often litres per minute. Heat transfer depends on both flow and the temperature difference between supply and return. Bigger pump settings are not automatically better.

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The temperature of water leaving a boiler or heat pump to supply radiators, underfloor heating or hot water systems.

In more detail

The supply temperature leaving the heat source for a particular circuit. It can change with controls and demand. Hot-water cylinder heating may require a different operating temperature from room heating, so the two should not be confused.

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A pipe or duct that safely removes combustion gases from a boiler, stove or fire.

In more detail

Carries combustion products to a safe discharge point. It differs from an extractor duct or a chimney used only for ventilation. Changes to terminals, liners or nearby construction require specialist assessment for the appliance concerned.

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A situation where a household struggles to afford adequate heating and energy services.

In more detail

Describes difficulty obtaining adequate energy services at an affordable cost; formal definitions vary across the UK. Poor efficiency, household income and energy costs can all contribute. It should not be confused with simply choosing to use less heating.

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A boiler that burns mains gas to provide heating and hot water.

In more detail

Burns mains gas and transfers heat to water. Condensing operation depends partly on return-water temperature. Installation and servicing need a suitably qualified Gas Safe registered engineer; controls and system condition affect real performance.

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The glass part of a window or door. Double and triple glazing reduce heat loss compared with single glazing.

In more detail

Includes the glass panes and their coatings, cavities and spacers. Whole-window performance also includes the frame and installation. Double glazing can vary considerably, so compare appropriate whole-window specifications rather than counting panes alone.

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A measure of how much heat a greenhouse gas traps in the atmosphere compared with carbon dioxide.

Also called: GWP

In more detail

Compares a greenhouse gas's warming effect with carbon dioxide over a stated time horizon, commonly 100 years. For refrigerants, the amount leaked also matters. A low GWP figure does not describe the equipment's electricity consumption.

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Pipework buried in the ground that collects heat for a ground source heat pump.

In more detail

Circulates a heat-transfer fluid through buried pipes to collect ground heat. Horizontal trenches and vertical boreholes have different space and design requirements. The ground collector must be sized for the building and local conditions.

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A heat pump that collects heat from the ground using buried pipework, boreholes or collector loops.

Also called: GSHP

In more detail

Moves heat collected from the ground into the home using electricity. The collector, heat pump and indoor distribution must be designed as one system. Ground temperatures are steadier than outdoor air, but installation feasibility is site-specific.

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A home that is more complex or costly to improve, often because of solid walls, unusual construction, access issues or heritage restrictions.

In more detail

A descriptive phrase for practical improvement difficulties, not a diagnosis that the home cannot be improved. Construction, exposure, access and heritage significance may call for different measures or specialist design.

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The amount of heat needed to keep a home or room at the desired temperature.

In more detail

Can mean energy needed over a period, normally in kWh, whereas a design heating load is power in kW. Always check the units. Demand changes with weather, temperature settings, building condition and occupancy.

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A component that transfers heat from one fluid or gas to another without mixing them.

In more detail

Transfers heat across a separating surface. The fluids normally remain separate, although the detailed arrangement varies. Surface area, cleanliness and temperature differences affect how effectively it works.

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The amount of heat escaping from a property through walls, roofs, floors, windows, doors, ventilation and draughts.

In more detail

Includes heat passing through the fabric and heat carried away by air exchange. The rate rises as the difference between indoor and outdoor temperature grows. Good design considers both routes and the required ventilation.

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A calculation used to estimate how much heat a property or room loses. It is essential for sizing heat pumps and radiators correctly.

In more detail

Uses dimensions, construction, temperatures and air-change assumptions to estimate heating load. A useful report states its inputs and limitations. Floor area alone or a boiler's previous rating is not a substitute for a proper calculation.

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A system that distributes heat from a central source to multiple buildings or homes.

In more detail

Distributes heat from shared sources to more than one customer or building. Networks can use different fuels and technologies. The network's source, losses, service arrangements and charging structure determine its practical and environmental performance.

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A low-carbon heating system that moves heat from outside air, the ground or water and upgrades it for space heating and hot water.

In more detail

Uses a refrigerant cycle and electricity to move heat, rather than generating all the heat directly from electricity. Its performance depends on source temperature, required delivery temperature, sizing and controls.

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Devices that control when and how heating operates, including thermostats, programmers, TRVs, smart controls and weather compensation.

In more detail

Coordinate heat-source operation and room comfort. Room thermostats, radiator valves and compensation controls perform different tasks. They should work together without unnecessarily restricting required system flow or repeatedly switching the heat source.

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A control setting that changes the heat pump flow temperature depending on the outside temperature.

In more detail

Defines how the target water temperature changes as outdoor temperature changes. Slope and offset have different effects. Adjustment should be gradual and informed by comfort and system guidance, rather than copying another home's settings.

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An improved type of electric storage heater that stores heat more efficiently and releases it in a more controlled way.

In more detail

Uses insulated storage and controlled heat release to make better use of stored off-peak electricity. Charging controls and tariff compatibility matter. It still uses direct electric resistance heating rather than the heat-moving process of a heat pump.

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A tank that stores hot water for taps, baths and showers. Heat pumps usually need a compatible hot water cylinder.

In more detail

Stores potable hot water, with heating provided through a coil, immersion heater or another arrangement. Volume, coil size, insulation and reheating time matter. It is not the same as an expansion vessel or a heating buffer.

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A heating system that combines two technologies, such as a heat pump and a gas boiler.

In more detail

Combines heat sources with controls deciding when each operates. Design should explain changeover conditions, running costs, emissions and maintenance needs. Having two heat sources does not automatically produce the most efficient arrangement.

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An indoor heat-pump module containing hydraulic components; the exact equipment inside depends on the system.

In more detail

An indoor hydraulic module used in some heat-pump arrangements. It may contain a heat exchanger, pump and controls, but contents vary by manufacturer. The term describes a package of components, not a separate heat source.

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An engineering analysis that tracks how heat and moisture move simultaneously through building walls, roofs, or floors

In more detail

Examines how heat and moisture behave together within a construction over time. The accuracy depends on material properties, weather, indoor conditions and assumptions. It helps evaluate risks but cannot compensate for poor detailing or water leaks.

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The quality of the air inside a home. It can be affected by moisture, ventilation, pollutants, mould, combustion appliances and occupancy.

Also called: IAQ

In more detail

Reflects airborne pollutants and moisture, not just whether air smells fresh. Ventilation, source control and maintenance all matter. A home can be warm and energy efficient yet still need better extraction or fresh-air provision.

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Electric heating panels that warm people and surfaces directly using radiant heat.

In more detail

Uses radiant heat to warm surfaces and people in its field of view. Room air is also warmed indirectly. It remains direct electric heating; comfort effects do not mean that every unit of electricity creates several units of heat.

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Plasterboard with insulation bonded to the back. It is often used internally on walls or ceilings.

In more detail

Combines plasterboard with an insulation layer. Thermal performance depends on thickness, material and installation. Joints, fixings, services and moisture-control details need proper design; the board alone is not a complete wall-insulation specification.

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Material used to slow down heat loss. Common examples include mineral wool, PIR, phenolic board, EPS, XPS, wood fibre, hemp, sheep’s wool and cellulose.

In more detail

Slows heat transfer rather than creating heat. The installed thickness, continuity, moisture condition and detailing influence results. Materials vary in fire, moisture, acoustic and structural properties as well as thermal conductivity.

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A fan that runs when needed, usually when a bathroom or kitchen is being used.

In more detail

Runs in response to a switch, humidity sensor or other demand signal. An overrun may continue extraction afterwards. It needs an adequate air path and effective outdoor discharge; short operation or obstructed ducting can limit moisture removal.

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Insulation fitted to the inside face of external walls. It can improve thermal performance but must be designed carefully to manage moisture risk.

Also called: IWI

In more detail

Adds an insulating lining inside an external wall. It reduces room space and changes the wall's temperature and moisture behaviour. Junctions, services, airtightness and drying potential require coordinated design, especially for older solid-wall construction.

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A variable-speed compressor used in many heat pumps. It can adjust output to match demand more efficiently.

In more detail

Varies compressor speed to adjust heating output within its operating range. It cannot reduce output indefinitely. Correct sizing, water volume, flow and controls still matter to avoid excessive cycling at low demand.

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A point where building elements meet, such as wall-to-roof, wall-to-floor or window-to-wall. Junctions are important for heat loss and thermal bridging.

In more detail

A meeting point between elements with potentially different thermal and moisture behaviour. Continuity of insulation, airtightness and rain protection needs attention here. A well-insulated main surface can still lose heat through a poorly detailed junction.

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A unit of power. Heating system output is usually measured in kilowatts.

Also called: kW

In more detail

A unit of power equal to 1,000 watts: the rate of using, generating or transferring energy. It does not describe energy used over a whole day. Keep kW separate from kWh when reading equipment specifications and bills.

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A unit of energy. Energy bills usually charge for electricity or gas in kWh.

Also called: kWh

In more detail

The energy transferred by a power of one kilowatt acting for one hour. Bills use this unit for energy quantity. Actual consumption depends on operating time and power, which can vary during use.

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A measure of a material’s thermal conductivity. Lower lambda values mean the material is better at resisting heat flow.

In more detail

Another name for thermal conductivity, commonly written as the Greek letter lambda and measured in W/(m·K). Lower values mean less heat flows through the material for comparable dimensions. Thickness is still needed to calculate resistance.

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A traditional breathable plaster often used in older solid-wall buildings.

In more detail

A lime-based internal finish used in many traditional buildings. Its moisture behaviour depends on the mix and coatings. Suitable finishes can support drying, but lime plaster is not a cure for an active leak or defective drainage.

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A building protected because of its special architectural or historic interest. Retrofit work may need special permissions and sensitive design.

In more detail

A building protected for special architectural or historic interest. Works affecting its character may require listed-building consent, separately from planning permission and building regulations. Obtain advice for the particular building and proposed changes.

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Insulation installed at ceiling level or roof level to reduce heat loss through the roof.

In more detail

At ceiling level it usually keeps the rooms warm while the loft remains outside the heated envelope. Roof-slope insulation creates a different arrangement. Ventilation, water tanks, wiring, downlights and access need suitable detailing.

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Heating that produces lower carbon emissions than traditional fossil fuel systems. Examples include heat pumps, heat networks and some biomass systems.

In more detail

Describes heating with comparatively lower greenhouse-gas emissions under stated assumptions. The electricity or fuel source, equipment efficiency and demand influence the result. Low carbon does not necessarily mean low purchase price or zero operating emissions.

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A heating system designed to work with lower water temperatures. Heat pumps are most efficient when supplying low flow temperatures.

In more detail

Uses water cool enough to improve compatible heat-source performance while still meeting room demand. Emitter area and operating time often need consideration. There is no single suitable water temperature for every building and heating system.

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A ventilation system that continuously extracts air from wet rooms such as kitchens, bathrooms and utility rooms.

Also called: MEV

In more detail

Continuously removes air from wet rooms, with replacement air entering through planned openings elsewhere. Systems may use a central unit or decentralised fans. Airflow must be measured and balanced with suitable air-transfer routes.

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A ventilation system that extracts stale air and supplies fresh air while recovering heat from the outgoing air.

Also called: MVHR

In more detail

Uses separate supply and extract air paths with a heat exchanger transferring heat between them. It needs designed ductwork, commissioning, filter changes and maintenance. Performance depends on installation quality and the building's leakage characteristics.

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A certification scheme covering low-carbon technologies such as heat pumps, solar PV and battery storage.

Also called: MCS

In more detail

Provides certification arrangements for small-scale renewable technologies and installers. Check that the organisation and technology are covered for the work proposed. Certification is useful evidence but does not replace checking the actual design and handover documents.

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A common insulation material made from glass or rock fibres. It is often used in lofts, cavities, floors and walls.

In more detail

Includes glass-wool and stone-wool products with different densities and applications. Correct thickness, support and fit are important; compression or gaps can reduce installed performance. Product suitability must be checked for the specific location.

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The relationship between moisture entering, moving through and leaving a building. Poor moisture balance can cause condensation, damp and mould.

In more detail

Looks at all sources and routes of moisture, including rain, ground water, leaks and indoor humidity, and how the building dries. Improving one route while blocking another can create unexpected problems.

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A monobloc heat pump is an all-in-one heating system where all the main components are housed inside a single outdoor unit.

In more detail

In an air-to-water arrangement, the main refrigerant components are assembled in the outdoor unit and water pipes normally connect it to the home. External water pipework needs appropriate insulation and frost protection designed for the system.

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Fungal growth that can occur where moisture, poor ventilation and cold surfaces are present.

In more detail

Fungi can grow on persistently damp surfaces and materials. Colour alone does not identify the species or health risk. Safe removal and investigation of the moisture source are both needed; repeatedly painting over growth does not resolve the cause.

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Ventilation driven by wind and temperature differences, usually through windows, vents, chimneys and gaps.

In more detail

Uses pressure differences caused by wind and temperature to move air through designed openings. Rates vary with weather and opening positions. It should not be confused with uncontrolled leakage through defects in the building.

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A broad description of construction systems such as some concrete-panel, steel-frame and system-built homes; identify the actual build-up before designing improvements.

In more detail

A broad description covering several construction systems rather than one uniform wall type. The actual frame, panels, cladding and alterations need identifying. Retrofit details suitable for masonry may not suit these structures.

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A boiler that burns heating oil to provide heating and hot water, common in some off-gas properties.

In more detail

Burns stored heating oil, so a suitable tank and delivery access are needed as well as the boiler and flue. System maintenance and fuel storage condition matter. Competent advice is needed before altering appliances or storage arrangements.

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A communication system that allows compatible boilers and controls to modulate heating output more efficiently.

In more detail

A communications protocol used by some boilers and controls. Compatibility and supported functions vary. It can enable more responsive temperature control, but simply connecting an OpenTherm-labelled product does not guarantee correct commissioning or savings.

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When a home becomes uncomfortably hot, often due to solar gains, poor ventilation, insufficient shading or high internal heat gains.

In more detail

Depends on temperatures, duration and the needs of occupants, rather than one hot afternoon alone. Solar gains, internal gains, heat storage, ventilation and shading interact. Adding insulation should be considered alongside summer comfort.

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A wall shared between two properties. It may need consideration during insulation, airtightness or ventilation works.

In more detail

Separates adjoining properties or units. Its construction and any cavity can affect sound, fire separation and heat loss. Work must respect the relevant structural and legal requirements; it is not simply another external wall.

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A standard covering the installation of energy-efficiency measures in existing buildings.

In more detail

Sets installation requirements for specified energy-efficiency measures in existing dwellings. It works alongside the wider retrofit process in PAS 2035. Ask which edition and certification requirements apply to the project rather than assuming a logo covers all work.

Further reading: BSI: PAS 2035/2030. Check current guidance for schemes and standards.

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The UK retrofit standard for assessing, designing and managing domestic retrofit projects using a whole-house approach.

In more detail

Sets out a coordinated whole-dwelling retrofit process, covering assessment, design, installation oversight and evaluation. It is more than a product specification. The required roles and evidence depend on the applicable standard and project arrangements.

Further reading: BSI: PAS 2035/2030. Check current guidance for schemes and standards.

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The highest heating demand expected during very cold conditions.

In more detail

The highest power demand considered in a design, under stated conditions. Heating, hot water and electricity can have different peaks and may not all occur together. It should not be confused with annual energy consumption.

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Moisture entering through the building fabric, often due to defects such as failed pointing, cracked render, roof leaks or blocked gutters.

In more detail

Water enters through an exposed part of the building, often following rain. The visible patch may be away from the actual defect because water can travel. Inspect roof details, gutters, openings and wall condition before treating the inside finish.

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Insulation installed around floor edges or foundations to reduce heat loss at junctions.

In more detail

Targets heat flow around the floor edge and its junction with walls or foundations. It is only part of the floor's thermal performance. Detailing must also maintain moisture protection and suit the structure.

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A rigid insulation board with good thermal performance for its thickness.

In more detail

A type of rigid foam insulation, often selected where a relatively thin build-up is needed. Thermal conductivity is only one consideration: moisture, fire classification, facings and system compatibility must be checked from the product specification.

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Solar panels that generate electricity from daylight.

Also called: PV

In more detail

The process of converting light into electricity using semiconductor cells. PV systems differ from solar thermal systems, which heat water. Output varies with daylight, orientation, shading and equipment performance.

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Polyisocyanurate insulation board. A rigid foam board commonly used in walls, floors and roofs.

In more detail

A rigid polyisocyanurate foam product commonly supplied as boards. Facings, joint treatment, gaps and fixing methods influence the complete construction. A board's advertised conductivity does not by itself establish the wall or roof U-value.

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Formal consent that may be needed for some external changes, such as external wall insulation, solar panels in sensitive areas or alterations to listed buildings.

In more detail

Controls certain development and changes of use. Some work can fall within permitted development, but conditions, local restrictions and protected buildings can alter the position. Building-regulations approval and listed-building consent are separate questions.

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A safety valve that releases pressure if a heating or hot water system becomes over-pressurised.

Also called: PRV

In more detail

A safety device that discharges when pressure exceeds its set limit. A discharge can indicate a problem elsewhere in the system. It must not be blocked, capped or treated as a routine means of pressure control.

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Energy accounted for at source, including the upstream energy needed to produce and deliver the energy used in the home.

In more detail

Accounts for energy used upstream to produce and deliver the energy supplied to the building, using specified conversion factors. It differs from delivered energy shown on a meter. The calculation method and factors must be stated.

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A measure of heat loss at junctions between building elements, such as around windows or where walls meet floors.

In more detail

Quantifies extra linear heat transfer at a junction, usually in W/(m·K). It is used with junction length in heat-loss calculations. It differs from a U-value, which describes heat transfer through an area.

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Checks carried out to make sure retrofit work has been assessed, designed, installed and recorded correctly.

Also called: QA

In more detail

Uses planned checks, evidence and corrective action throughout a project. A final photograph alone may not show hidden defects. Useful assurance includes appropriate inspections before work is covered and records of commissioning and handover.

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A measure of thermal resistance. Higher R-values mean better resistance to heat flow.

In more detail

Thermal resistance depends on material thickness divided by thermal conductivity. Higher resistance means less heat flow through that layer. It does not describe a whole construction unless all relevant layers and effects are included.

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A heat emitter that transfers heat from hot water into a room.

In more detail

Transfers heat to a room through both convection and radiation. Its output depends strongly on the temperature difference between the water and room air. Catalogue ratings should be adjusted to the proposed system conditions.

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Reduced Data Standard Assessment Procedure. The method used to assess the energy performance of existing UK homes for EPCs.

In more detail

Uses a site survey and prescribed conventions to assess existing dwellings where full construction data is unavailable. Some inputs may be assumed under evidence rules. The resulting EPC is a standard comparison, not a forecast of a particular household's bill.

Further reading: Government: SAP and RdSAP. Check current guidance for schemes and standards.

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The working fluid inside a heat pump or refrigeration system. It absorbs and releases heat as it changes pressure and state.

In more detail

A working fluid that absorbs and releases heat as pressure and state change in a refrigeration cycle. It is normally separate from the radiator water. Refrigerant type affects equipment design, safety arrangements and environmental considerations.

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The process used by heat pumps, fridges and air conditioners to move heat. The main stages are compression, condensation, expansion and evaporation.

In more detail

Moves heat through compression, heat release, expansion and heat absorption. A heat pump uses the useful heat released on the warm side. Individual components operate together, so faults cannot reliably be diagnosed from one temperature reading.

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The amount of water vapour present compared with saturation at the same temperature, expressed as a percentage.

Also called: RH

In more detail

The ratio of actual water-vapour pressure to saturation pressure at the same temperature, expressed as a percentage. Cooling air without removing moisture raises its relative humidity. A room reading does not reveal moisture conditions inside a wall.

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An external finish applied to walls. It may be used as part of an external wall insulation system.

In more detail

A protective or decorative coating applied to an outside wall or insulation system. The correct mix, reinforcement and details depend on the substrate. Cracking, poor junctions or unsuitable coatings can allow rain in or impede drying.

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Energy from sources that naturally replenish, such as sunlight, wind, water and ambient heat.

In more detail

Comes from sources replenished by natural processes. It does not mean every installation has zero environmental impact. Equipment manufacture, operation, fuel supply and the energy system still matter when comparing options.

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Improving an existing building to make it more energy efficient, comfortable, healthy and lower carbon.

In more detail

Improves an existing building rather than constructing a new one. Successful work balances energy, comfort, health, moisture and durability. A coordinated sequence avoids one improvement making a later measure harder or causing unintended problems.

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A property assessment that looks at the building condition, occupancy, energy use, ventilation, heritage issues and suitability for improvement measures.

In more detail

Collects information needed to plan improvements, including condition, construction, occupancy and ventilation. It should identify uncertainties and further investigations. It is broader than simply listing the EPC's recommendations or measuring room sizes.

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A qualified person who gathers the property information needed for a retrofit project.

In more detail

Surveys and records the information used by the wider retrofit team. The assessor's scope and competence should match the building. Gathering information does not make the assessor the designer or coordinator of every measure.

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A qualified person responsible for overseeing the retrofit process under PAS 2035, including risk management and coordination.

In more detail

Coordinates the retrofit process and relevant risk management under the applicable project framework. The role brings assessments, designs, installation information and evaluation together. It does not remove the responsibilities of designers or installers.

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The technical design of energy-efficiency measures, including specifications, drawings, moisture risk and ventilation requirements.

In more detail

Turns survey findings and objectives into construction and system details. It should specify interfaces, moisture control, ventilation and performance requirements. A sales quotation naming a product is not necessarily a complete retrofit design.

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A contractor who installs energy-efficiency measures such as insulation, heating, ventilation or renewables.

In more detail

Carries out the specified work using suitable competence and project procedures. Product knowledge alone is not enough where building defects or complex interfaces are involved. Evidence, commissioning and a clear handover are part of good delivery.

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A staged plan for improving a home over time, often following a whole-house approach.

In more detail

Sets out improvements and their sequence, including interactions and future work. It can be staged around budgets and maintenance opportunities. It should be based on the actual building, rather than a universal list of products.

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The temperature of water returning from radiators or underfloor heating back to the boiler or heat pump.

In more detail

The water temperature coming back from an emitter or circuit. The difference from flow temperature helps describe heat delivery and system operation. It should be interpreted with flow rate and the particular heat-source requirements.

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Ground moisture drawn upwards through porous building materials. A low damp patch alone does not prove rising damp.

In more detail

Describes liquid moisture moving upwards through porous materials in contact with the ground. It is often misdiagnosed. Ground levels, drainage, leaks, salts and other moisture routes need investigation before a remedial damp-proofing treatment is selected.

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A detailed calculation of heat loss for each room, used to size radiators, underfloor heating and heat pumps.

In more detail

Calculates each room's design heating load using its size, surfaces, construction and ventilation assumptions. It helps distribute heat correctly rather than just estimating a total for the home. Survey assumptions and design temperatures should be documented.

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Standard Assessment Procedure. The UK method for assessing the energy performance of new dwellings.

In more detail

The Standard Assessment Procedure is a government methodology for modelling dwelling energy performance. It uses defined inputs and assumptions rather than actual bills. Full SAP is commonly used where detailed construction information is available; RdSAP adapts the approach for existing homes.

Further reading: Government: SAP and RdSAP. Check current guidance for schemes and standards.

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A seasonal measure of heat pump efficiency over a period of heating operation.

Also called: SCOP

In more detail

A standardised seasonal efficiency figure calculated under defined climate and operating conditions. It is useful for comparing products on a like-for-like basis, but is not a promise of the performance achieved in an individual home.

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A measure of heat pump performance over time, comparing useful heat output to electricity input.

Also called: SPF

In more detail

Compares useful heat supplied with electricity consumed over a stated period and measurement boundary. Ask whether pumps, immersion heating and other auxiliaries are included. Figures with different boundaries or weather conditions are not directly comparable.

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An additional pane or frame fitted inside an existing window to improve thermal performance, comfort and noise reduction.

In more detail

Adds a separate inner glazing layer while retaining the existing window. Performance depends on fit, seals, cavity and design. It can help where replacing original windows is unsuitable, but moisture and ventilation arrangements still need thought.

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A place where pipes, cables or ducts pass through the building fabric. Poorly sealed penetrations can cause draughts and heat loss.

In more detail

An opening where a pipe, cable or duct passes through a building layer. It may need separate airtightness, fire, acoustic and weather seals. Filling a visible gap without understanding those requirements can be inappropriate.

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A meter that records energy use and sends readings automatically to the supplier.

In more detail

Records energy consumption and can send readings to the supplier using a communications system. An in-home display helps show usage but does not control every appliance. Tariffs and data arrangements should be checked with the supplier.

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Heat gained from sunlight entering a building, especially through windows.

In more detail

Sunlight becomes useful heat when absorbed by the building or its contents. Window orientation, glass, shading and season affect the amount. Helpful winter gains can become unwanted summer heat, so design needs both considerations.

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Solar photovoltaic panels that generate electricity.

In more detail

Photovoltaic modules turn daylight into electricity, usually through an inverter supplying usable AC electricity. Generation varies with weather, orientation and shading. Panel peak capacity in kWp differs from energy generated over a year in kWh.

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Solar panels that use sunlight to heat water.

In more detail

Uses collectors to transfer solar heat into a hot-water system, normally through a cylinder and heat exchanger. It produces heat rather than electricity. Design should consider storage, controls and backup water heating.

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Insulation added above or below a solid concrete floor.

In more detail

May be installed above an existing slab or as part of a rebuilt floor. Raising the floor affects doors, stairs and thresholds. Moisture protection, perimeter details and the load-bearing build-up need coordinated design.

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A wall without a cavity, often found in older homes. Solid walls can be insulated internally or externally.

In more detail

Has no continuous cavity suitable for ordinary cavity-fill insulation. Brick, stone, earth and other constructions behave differently. Condition, rain exposure, finishes and drying ability must be considered before deciding on internal or external insulation.

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Heating used to warm the rooms in a home.

In more detail

Heat supplied to occupied rooms for comfort, separate from hot water used at taps. Its demand changes with weather and building performance. Separating the two helps explain bills and size or compare heating systems.

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The written technical detail describing how retrofit measures should be installed.

In more detail

Sets out the required materials, workmanship, details and performance for the work. It should be specific enough to install and inspect against. A product brochure or short quotation does not describe every junction and interface.

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A "split" system is divided into separate indoor and outdoor units.

In more detail

Separates heat-pump components between indoor and outdoor units, commonly with refrigerant connections between them in an air-to-water split arrangement. The exact configuration varies. Installation must follow the manufacturer's requirements and applicable competence rules.

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A timber floor with a ventilated void underneath. It can often be insulated between the joists.

In more detail

Floorboards and joists sit above a void rather than directly on the ground. Moisture, timber condition and underfloor ventilation need assessment. Insulation should reduce heat loss without creating damp or blocking required air paths.

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A boiler that works with a hot water cylinder but has many components built into the boiler unit.

In more detail

Supplies a wet heating system and usually a separate hot-water cylinder, with certain system components built into the appliance. The exact layout varies. Cylinder capacity and reheating performance remain important hot-water considerations.

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An area where heat passes through the building fabric more easily, often at junctions, steelwork, lintels or gaps in insulation.

In more detail

A local route where heat flows more readily because of geometry, materials or gaps in insulation. It can increase heat loss and lower nearby surface temperatures. Continuous insulation and careful junction design help reduce its effects.

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How easily heat passes through a material. Lower conductivity means better insulation performance.

In more detail

A material property describing how readily heat is conducted, commonly in W/(m·K). Lower values resist heat flow better for equal thickness. Moisture and test conditions can influence values; whole-element performance also depends on thickness and construction.

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The parts of the building that separate heated spaces from unheated spaces or outside air.

In more detail

The boundary around the heated part of the building, which may not follow the outside walls everywhere. Identifying it helps place insulation and airtightness layers consistently. Unheated lofts and attached garages can sit outside it.

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Using an infrared camera to examine surface-temperature patterns as part of a building investigation.

In more detail

Shows surface-temperature patterns, not a direct view through walls. Weather, heating, reflections and surface finishes affect interpretation. It can support an investigation but cannot by itself prove the presence of damp or quantify every heat loss.

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The ability of materials such as brick, concrete or stone to absorb, store and release heat.

In more detail

Describes the ability to absorb and release heat, rather than resist heat flow. Its usefulness depends on exposure, temperatures and timing. Heavy materials can moderate temperature swings but do not replace insulation or a summer ventilation strategy.

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A control that turns heating on or off, or modulates it, based on temperature.

In more detail

Measures temperature at its position and signals a control system. Location matters: sunlight, draughts and nearby heat sources can distort its view of room comfort. A room thermostat differs from a boiler water-temperature setting.

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A valve fitted to a radiator that helps control the temperature in an individual room.

Also called: TRV

In more detail

Regulates water through an individual radiator in response to nearby air temperature. It does not normally set the boiler's water temperature. Valve arrangements need coordination with the main thermostat and the system's minimum-flow requirements.

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A construction type where the main structural frame is made from timber.

In more detail

Uses a timber structural frame, with sheathing, insulation and finishes forming a layered wall or roof. The outside appearance may resemble masonry construction. Moisture management, ventilation cavities and fire details must suit the actual build-up.

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A small controllable vent, usually in a window frame, that provides background ventilation.

In more detail

A small controlled opening normally providing background air to a room. It needs to be considered with extraction elsewhere and air-transfer paths. It is not a substitute for all ventilation needs or a defect to seal during draught-proofing.

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A UK government-endorsed quality scheme used for many retrofit and energy-efficiency works.

In more detail

A government-endorsed quality scheme covering registered businesses within defined work categories. Check current registration and scope, not just a badge on an advert. Registration does not remove the need for a suitable design, contract and project evidence.

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A measure of how much heat passes through a building element, such as a wall, roof, floor, window or door. The lower the U-value, the better the insulation performance.

In more detail

Describes heat flow through an area of a complete building element per degree of temperature difference, normally in W/(m²·K). Lower values mean less heat transfer. It differs from conductivity, which describes a material rather than the whole element.

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A heating system with pipes or electric elements installed in or under the floor. Wet underfloor heating can work well with heat pumps because it can run at low temperatures.

Also called: UFH

In more detail

Can use circulating water in pipes or electric resistance elements. These systems have different running characteristics. Output depends on floor construction, coverings, available area and temperatures; suitability should be checked against each room's heat loss.

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Insulation installed below a floor, commonly between suspended timber floor joists.

Also called: UFI

In more detail

Describes insulation placed below a floor surface, often between or beneath suspended timber joists. Support, wind washing, services and moisture behaviour need attention. It should not obstruct the ventilation required to keep the floor structure healthy.

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An area such as a loft, garage, cellar or porch that is not normally heated.

In more detail

A space not normally maintained at the dwelling's comfort temperature. Heat can still flow into it from neighbouring rooms. Whether it belongs inside or outside the thermal envelope affects insulation and heating calculations.

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A layer designed to stop or reduce water vapour passing through a building element.

In more detail

An informal name for a layer with high resistance to water-vapour diffusion. The specified resistance and installation details matter more than the label. It is not automatically the same as an airtightness layer or a waterproof covering.

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A material used to control the movement of moisture vapour through walls, roofs or floors.

Also called: VCL

In more detail

Limits vapour movement according to the design, rather than necessarily blocking it completely. Continuity at joints and penetrations matters. Its position and resistance should suit climate, materials and drying paths; it is not universally correct to add one everywhere.

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The controlled supply and removal of air from a home. Ventilation helps manage moisture, odours, pollutants and indoor air quality.

In more detail

Deliberately replaces indoor air to manage moisture and pollutants. Supply, extraction and transfer routes must work together. Reducing uncontrolled leakage should not reduce the fresh-air provision needed for occupants or safe appliance operation.

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Heat lost when warm indoor air is replaced by colder outside air.

In more detail

Heat carried away when indoor air is replaced by cooler outdoor air. Both necessary ventilation and uncontrolled leakage can contribute. Heat recovery may reduce some losses, but maintaining suitable air quality remains essential.

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The amount of air supplied to or removed from a building over time.

In more detail

Quantifies airflow, often in litres per second, cubic metres per hour or air changes per hour. These units describe different comparisons. Check whether a figure is a design requirement, a measured airflow or a pressure-test result.

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A planned approach to providing enough fresh air before and after retrofit works.

In more detail

A coordinated plan for outdoor air supply, extraction, transfer routes, controls and maintenance. It should consider occupancy and the completed building after improvements. Buying one fan does not automatically establish a suitable whole-dwelling strategy.

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A vessel used in some heat pump systems to increase system water volume and help stable operation.

In more detail

Adds water volume to a heating circuit, helping meet a heat pump's minimum volume requirements. It is not necessarily a hydraulic separator or hot-water store. Whether it is needed depends on the manufacturer's requirements and system design.

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A roof construction where insulation is installed above the roof deck, helping keep the structure warm.

In more detail

Usually places insulation above the structural deck or supporting roof structure in the relevant roof design. The full build-up includes moisture control and weather protection. The phrase does not simply mean a roof that feels warm indoors.

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A heat pump that collects heat from a water source such as a lake, river, pond, well or open-loop system.

Also called: WSHP

In more detail

Collects heat from water using an appropriate open-loop or closed-loop arrangement. Source temperature, flow, water quality and permissions can affect feasibility. Specialist environmental and system-design advice is normally needed.

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A control method that adjusts heating flow temperature based on the outside temperature.

In more detail

Uses outdoor temperature to adjust the target heating-water temperature. It needs an appropriate heating curve and system setup. It differs from merely turning heating on when the weather forecast predicts a cold day.

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Protecting a building from rain, wind and external moisture.

In more detail

Controls rain and wind at roofs, walls, openings and joints. It should allow the complete construction to manage moisture appropriately. Applying an impermeable coating without diagnosing water entry can conceal defects or hinder drying.

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Ventilation that extracts moist air from bathrooms, shower rooms, kitchens and utility rooms.

In more detail

Extracts air from rooms with concentrated moisture or pollutants. Here, wet room means spaces such as kitchens and bathrooms, not only a level-access shower room. Ducting, replacement air and measured flow determine effectiveness.

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A retrofit method that considers the whole property rather than installing individual measures in isolation.

In more detail

Considers the home as interacting construction, services and people. It avoids choosing isolated measures without checking their combined effect. Ventilation, moisture, energy, comfort, heritage and future maintenance should be considered together.

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A staged improvement plan that considers insulation, heating, ventilation, moisture, comfort, cost and future works.

In more detail

Records a coordinated sequence of improvements tailored to the dwelling and household objectives. It can allow work in stages while anticipating interfaces and later measures. It should be updated when condition, budgets or planned work change.

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The area around the window opening. Reveals are important because they can create thermal bridges if not insulated properly.

In more detail

The sides, head and sill surfaces of a window opening. Insulation, weather seals and airtightness need to connect around them. A reveal left untreated can remain a local cold surface even after the main wall is improved.

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Extruded polystyrene insulation. A rigid foam insulation often used where moisture resistance and compressive strength are needed.

In more detail

Extruded polystyrene is a rigid foam used where specified strength and moisture resistance are useful. Those properties do not make every XPS board suitable for every application. Fire, load, thickness and system requirements still need checking.

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A claim about carbon emissions that needs a clear boundary, time period and accounting method.

In more detail

A claim that needs a defined boundary, period and method. Direct fuel use, purchased energy, embodied emissions and offsets are different considerations. Without that explanation, it is impossible to compare the claim reliably.

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Heating with no combustion emissions at its point of use; electricity supply and equipment manufacture can still cause emissions.

In more detail

Produces no combustion emissions at the point of heating use, unlike an appliance burning fuel indoors or on site. It does not mean zero lifecycle or electricity-generation emissions. Efficiency still determines how much electricity the service requires.

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Dividing a heating system into separate areas that can be controlled independently, improving comfort and efficiency.

In more detail

Allows different areas or circuits to respond to separate temperature or time demands. Zone design should maintain suitable flow and stable heat-source operation. Too many independently closing zones can be problematic for some systems.

Link to this term