EPC Improvement Explorer
Explore how insulation, heating and solar could affect your home’s energy rating.
Use this as a rough estimate
Try one change at a time to see which improvements are worth looking into. The explorer uses a simplified model and typical values where an assessor would use more detail.
For an official Energy Performance Certificate (EPC), an accredited assessor visits your home and uses the full set of assessment data available, including measurements, construction details, heating equipment and evidence of insulation. The points and bands shown here are estimates for comparing scenarios. Your assessed rating may differ.
About your home
Use the total floor area on your EPC if it reflects the home today. Include all storeys and any existing room in the roof. Leave out an unfinished loft.
Enter a total floor area greater than zero.
The property type suggests 3 exposed walls. You can override this if the layout differs. Count walls facing outside and leave out walls shared with a neighbouring home. The year built is used when you choose Cavity, as built or Assume from year built for loft insulation. Unsure when your home was built? Try the Property History guide (opens in a new tab).
Estimated change
SAP points
See estimated scores and bands
Try some changes
Set up the current example, copy it across, then change one option to see its effect. Try several changes together to compare a package.
Which doors should I count?
Count front, back and other external doors where your home loses heat. Leave out internal doors and doors to heated access corridors. Count a double external door as two leaves.
Count each glazed patio, sliding or French door set as one patio door. Use this count for doors where glass covers at least 60% of the whole opening, including the frame. Enter each door under one count only.
The model assumes a standard opaque external door of 1.85 m². Each patio door adds 2 m² of glass using your window glazing choice. BRE RdSAP conventions 2.14 and 3.09
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What counts as a room in the roof?
Think of a bedroom or home office built into the roof space, often with a sloping ceiling. It must be reached by a permanent, fixed staircase you can walk up and down facing forwards. Choose No if you reach the loft by a ladder or pull-down steps, or if it’s an unfinished storage loft.
For loft insulation, look at the insulation above the ceiling below any unheated loft. For a roof room, think about the insulation around the room itself.
Dormer windows and flat roofs. A dormer sticks out from a sloping roof to make room for a window and extra headroom. Heat can escape through its glazing, side walls and the flat roof above it. Older glazing or a poorly insulated flat roof can increase heat loss. Better glazing and insulation can reduce it.
A detailed EPC assessment can account for the walls and flat ceilings of larger dormers separately. This explorer uses one insulation choice for the whole roof room, so it gives a rough comparison for homes with dormers. BRE guidance on roof rooms and dormers
Which fuel and heating system should I choose?
Choose the fuel used by your main heating. Electric includes heat pumps, storage heaters and electric room heaters. A heat pump uses electricity to move heat into your home. Solid fuel includes wood logs, pellets, coal and smokeless fuel. If a log stove just tops up another system, choose the system that mainly heats your home.
A condensing gas boiler recovers extra heat from the gases leaving the boiler, so it generally uses less gas for the same heat than an older non-condensing boiler. Combi, system and regular describe how the boiler is set up. Check the model number or manual if you’re unsure whether it condenses. Government guidance on condensing boilers
What is a phase-change heat battery?
It stores heat for later. When warmed, a special material inside melts and absorbs heat. As the material cools and turns solid again, it releases that heat. Some models use it to heat tap water on demand, doing a similar job to a hot-water cylinder.
A solar electricity battery stores electricity that can power appliances. A phase-change heat battery gives you heat. Choose Yes if the product label or manual confirms you have phase-change heat storage, or Unsure if you can’t tell.
RdSAP 10 can record phase-change heat storage in a note on the EPC. Its performance is outside the rating calculation, so changing this answer gives no points in the explorer. BRE RdSAP specification, addendum 17
Loft insulation here means insulation above the ceiling below the unheated part of the loft.
Smart meters and phase-change heat batteries are recorded here for comparison. They add no points in this tool. RdSAP records smart meters for statistics and can note phase-change heat storage in the EPC addendum. BRE RdSAP specification
How the estimates work
The model estimates heat loss from assumed dimensions, ventilation and illustrative U-values (how easily heat passes through a building element). It uses one example heating climate and a fixed window area plus any patio door glazing. The model estimates a room in the roof at 60% of the home’s footprint. It uses the current roof-room choice to work back from the total floor area. If you add or remove a roof room in the changed setup, the model adjusts the total area while keeping the same footprint.
For exposed walls, the example uses a rectangular footprint and assumes the front and back face outside. An RdSAP assessment measures exposed perimeter by storey. The age options use the England age bands and the cavity wall and pitched-loft defaults from the RdSAP specification. If age is unknown, those two options use example U-values of 1.5 and 0.40 W/m²K respectively. Choose the construction and insulation you know about where available. BRE RdSAP specification, sections 2, 3 and 5 For help researching the home’s age and construction, see the Property History guide (opens in a new tab).
Heating efficiencies are illustrative. TRVs (thermostatic radiator valves) and room thermostats reduce modelled heat demand for wet radiator systems using example adjustments. Actual RdSAP control treatment depends on the full control package. Boilers and heat pumps are assumed to supply hot water. Room heaters and stoves use separate electric water heating in the model. The storage-heater example assumes 80% of space-heating electricity is bought at the off-peak rate. Lighting and ventilation use simplified allowances.
Enter the panel area as a share of the whole roof, including slopes without panels. The model assumes a 30° pitched roof, 0.20 kWp of panels per m² and a yield of 850 kWh per kWp per year. Actual generation depends on panel output, location, pitch, orientation and shading.
Choose how the panels supply the home. The model credits electricity used in the home and adds export credit only for a system that can export to the grid. It assumes 35% of generation can be used on site, or 65% with a PV electricity battery, capped at modelled electricity demand. With the same modelled value for self-use and export, a battery can shift electricity from export to self-use without changing the points.
Count a separate cylinder that stores domestic hot water. A combi boiler with no separate cylinder is a “No”. The model adds a standard storage loss of 300 kWh/year for a cylinder with a jacket or factory insulation, or 1,100 kWh/year for a bare cylinder. With no cylinder there is no cylinder storage loss. Water-heating fuel and efficiency are set by the heating choice. A phase-change heat battery stores heat. The separate PV battery option stores electricity.
The model uses the RdSAP 10 Table 32 fuel prices and an RdSAP rating equation to convert modelled energy costs into points. EPC points reflect energy cost under standard assumptions. Actual bills depend on your tariffs and how you heat your home. The model omits factors including solar gains through windows, secondary heating, extensions and product-specific data.
BRE RdSAP specification and conventions · mywarmhome.co.uk EPC guide