VENTILATION / MY WARM HOME
Mechanical ventilation with heat recovery.
Continuous fresh air, with heat transferred from outgoing air to incoming air.
01
Understand
Balanced mechanical supply and extract.
02
Follow the air
Separate air streams meet at the heat exchanger.
03
Recover the heat
Benefits, efficiency and limitations.
04
Design & check
Airtightness, ducts, controls and commissioning.
THE SHORT VERSION
Ventilation with less heat lost.
Mechanical ventilation with heat recovery (MVHR) continuously extracts stale, moist air from wet rooms and supplies filtered outdoor air to living rooms and bedrooms.
Before outgoing air leaves the building, a heat exchanger transfers some of its warmth to the incoming air. In a typical plate heat exchanger the air streams remain separate: heat moves across the exchanger surfaces without the two flows normally mixing.
MVHR is not a replacement for heating and is not the same as a heat pump. Its purpose is to deliver reliable fresh air while reducing ventilation heat loss. The unit, ductwork, airtightness, controls, commissioning and maintenance must all work together.
01 / BALANCED SUPPLY & EXTRACT
Four parts of the same system.
Unlike extract-only MEV, MVHR mechanically moves air both into and out of the home. It normally runs continuously at background speed and increases to boost during high-moisture activities.
01
Supply air
Filtered outdoor air is delivered to habitable rooms, normally bedrooms and living spaces.
02
Extract air
Stale air is drawn from kitchens, bathrooms, utility rooms and other designated wet rooms.
03
Heat exchanger
A core transfers heat from outgoing air to incoming air without normally mixing the air streams.
04
Exhaust & intake
Separate outdoor terminals, filters and ductwork complete the two air paths.
MVHR is designed as a balanced whole-house system. Standard background trickle vents are not normally the planned supply route; suitability of existing openings and purge ventilation must be assessed as part of the complete design.
02 / FOLLOW THE AIR
How does MVHR work?
MVHR has two separate mechanical air streams. The exchanger recovers heat from the exhaust stream before it leaves the building.
01 / Fresh air enters
The supply fan draws outside air through an appropriately positioned intake and a filter.
02 / Warm, moist air is extracted
A separate fan collects stale air from the wet rooms through the extract duct network.
03 / Heat transfers across the core
Warm outgoing air passes one side of the heat exchanger; colder incoming air passes the other. Heat transfers across the separating surfaces.
04 / Tempered air is supplied
Filtered, pre-warmed air passes through supply ducts to bedrooms and living rooms; extracted air is discharged outdoors.
05 / Moisture is managed
Condensate produced within the unit must discharge safely through a correctly detailed drain, with frost protection where required.
03 / HEAT RECOVERY EXPLAINED
What exactly gets recovered?
The outgoing air has already been warmed by the home. MVHR recovers some of that thermal energy rather than sending it all straight outdoors.
The core transfers heat, not free heating.
If it is colder outside than indoors, incoming air can leave the exchanger warmer than the outdoor temperature. The system still needs an effective heating source to maintain the room temperature, and both fans consume electricity.
Efficiency depends on the real installation.
The product’s tested heat-recovery figure is not a guaranteed whole-house seasonal saving. Actual performance depends on airflow balance, insulation and airtightness of ducts, unit location, external temperatures, filters, controls and how the occupants use the system.
Summer bypass and frost protection
Many units can bypass heat recovery when conditions suit, reducing unwanted heat transfer. This is not mechanical air conditioning and cannot by itself guarantee a cool home. Frost protection and condensate arrangements also need to be designed for the unit and climate.
THE EQUIPMENT
The unit is only part of the installation.
Select supply and extract terminals for their room duties, with a quiet unit, accessible filters, appropriate outdoor intake and exhaust positions, insulated cold-side ducts and a suitable condensate connection.
A system can have an impressive headline recovery rating but perform poorly when ductwork is leaky, crushed, inadequately insulated or badly balanced.
03 / THE BENEFITS
Continuous air change with heat recovery.
In the right building, MVHR combines consistent ventilation with lower heat loss than an otherwise comparable extract-only arrangement.
Filtered outdoor supply air
Fresh air can be filtered before it reaches bedrooms and living areas. Filter selection and regular replacement matter.
Moisture and pollutant removal
Wet rooms have planned continuous extract, with boost available for cooking and bathing.
Reduced ventilation heat loss
Heat from outgoing air is transferred to the incoming supply, reducing the heating energy needed to temper that fresh air.
Less dependence on windows for background ventilation
The normal background air-change route is controlled mechanically. Openable windows or other suitable purge ventilation are still useful and may be required.
03 / KNOW THE LIMITATIONS
What needs careful consideration?
01
Airtightness
Uncontrolled leakage can bypass the designed system and weaken heat-recovery benefits.
02
Duct space
Separate supply and extract duct networks need routes, suitable terminals and access, which may be disruptive in retrofit.
03
Maintenance
Filters need checking and changing; dirty ducts, grilles and cores can reduce performance.
04
Noise & energy
Two fans use electricity. Poorly sized ducts, badly located units or excessive speeds can create unwanted noise.
Condensate must drain correctly, cold ducts need appropriate insulation and the installer must account for frost protection, summer controls and access for ongoing maintenance.
Ventilation alone does not diagnose condensation, mould or damp. Leaks, thermal bridges, heating patterns and other building defects may need separate investigation.
03 / COMPARE THE OPTIONS
MEV, intermittent extract or MVHR?
There is no automatic winner. Assess the whole home, rather than choosing a fan by its brochure efficiency.
Natural and intermittent ventilation
Air change is provided through openings and fans operating when needed. Performance can depend more on wind, temperature and occupant use.
MEV — mechanical extract ventilation
Continuous extract removes air from wet rooms, and replacement air enters through designed background ventilators. It does not normally recover heat.
MVHR — mechanical ventilation with heat recovery
Balanced mechanical supply and extract are linked through a heat exchanger. It can reduce ventilation heat loss, but needs a suitable level of airtightness and space for two duct routes.
The choice must also consider any open-flued or other combustion appliances, existing vents, fabric condition, household needs and the wider retrofit plan.
04 / DESIGN, COMMISSION, MAINTAIN
Eight checks for effective MVHR.
01
Assess the whole dwelling
Record airtightness, occupancy, moisture loads, room usage, existing ventilation, building condition and combustion appliances.
02
Set the room-by-room airflow
Design appropriate continuous and boost rates, then size supply and extract terminals and fan duties.
03
Plan both duct routes
Keep ductwork short and well supported, with adequate sizes, limited resistance and appropriate fire and acoustic detailing.
04
Insulate and seal the ducts
Control leakage and heat loss, especially on intake and exhaust runs in cold spaces; follow the product design requirements.
05
Detail condensate and frost control
Provide a correctly trapped/drained condensate route as required and protect operation in cold weather.
06
Choose practical controls
Allow sensible boost, bypass and filter alerts, with clear instructions the household can use.
07
Commission & balance
Measure supply and extract rates at terminals, balance the whole system and hand over records and settings.
08
Maintain access and filters
Keep the unit, filters, ducts, terminals and drain accessible; inspect and clean at the intervals specified by the manufacturer.
A system needs verified flow rates at its terminals, an appropriate overall supply/extract balance, a documented handover and straightforward maintenance instructions.
BUILDING REGULATIONS & GUIDANCE
Use the guidance applicable to the work.
Check the relevant UK nation
Requirements vary between England, Wales, Scotland and Northern Ireland, and may depend on the date and scope of building work.
England — Approved Document F
The 2026 edition and earlier editions apply to different regulatory circumstances. Follow the applicable requirements for design, testing, commissioning and homeowner information.
Read the official guidance
Read the 2026 edition
IS MVHR SUITABLE FOR YOUR HOME?
Start with the building and the available duct space.
MVHR is commonly considered for homes with good airtightness and a planned whole-house ventilation route, including new builds and comprehensive retrofits.
In an existing home, achieving continuous supply and extract routes may involve opening ceilings and boxing in ducts. Existing background vents, loft conditions, filter access, intake positions, condensate drainage and the effect on combustion appliances all need to be assessed.
A mould or condensation problem alone does not mean MVHR is the solution. Identify the underlying moisture and building issues before specifying equipment.
2
separate air streams — linked by one heat exchanger.
MY WARM HOME VIEW
Good heat recovery starts with good ventilation design.
MVHR can help maintain indoor air quality while reducing ventilation heat loss, but only when the home, duct network, airtightness and installation details work together.
BEFORE YOU INSTALL MVHR
Design the air path first. Choose the unit second.
A balanced, commissioned and maintainable system is the goal — not simply a published heat-recovery percentage.