Warm home check: methodology

Where your data goes

Nowhere. Everything is worked out in your browser. The property reference, the EPC figures and the income you enter are not sent to us or stored, and the printout is made by your own browser.

The heat a home needs

Every Energy Performance Certificate estimates how much heat a home needs a year for space heating and for hot water. Those figures come from the government’s standard assessment method, SAP, which assumes a standard household heating the home to set temperatures for set hours each day. That makes them a fair yardstick for “can this home be kept warm”: it’s the heat needed to reach a recognised standard, whatever the current household actually does.

From heat to fuel

• Gas boiler: heat divided by the boiler’s efficiency, starting at 85%, the cautious end of real-world condensing boilers.
• Heat pump: heat divided by its seasonal efficiency (SCOP), starting at 3, the low end of what installed heat pumps achieve in UK homes.
• Storage heaters and direct electric heaters: one kWh of electricity for one kWh of heat. Storage heaters are priced on Economy 7: the whole home’s electricity at Ofgem’s average multi-rate unit rate for the region, with the multi-rate standing charge. A household that uses more of its electricity at night than Ofgem assumes will pay a little less.

Both efficiencies can be changed on the page.

Prices

The price cap for 1 October 2026 to 31 December 2026 in the home’s own electricity region, paying by direct debit, from Ofgem’s regional tables. The whole bill adds the rest of the household’s electricity, starting at Ofgem’s typical 2,500 kWh a year, and the standing charges for each fuel the home uses. The regional price pages give every region’s rates.

A January week

Heating isn’t spread evenly over the year. A January week takes January’s share of a year’s heating and hot water, 16% for the month in a typical gas-heated home, the same pattern our tariff and direct debit tools use. It’s the week that matters for a household on a tight budget.

Affordability

If you enter the household’s weekly income, the check shows the whole energy bill as a share of it. There is no single UK definition of fuel poverty: Wales counts a household that needs to spend more than 10% of its income on keeping warm; Scotland uses 10% of income after housing costs together with a minimum income test; England uses a measure based on energy efficiency and income. The share is an indication, not an assessment under any of them.

What it can’t tell you

• It isn’t a hazard assessment. Whether a home has an excess cold or damp and mould hazard is for a trained assessor; this gives them the running-cost side of the picture.
• An EPC is only as good as its survey and its age. Insulation added or removed since, or a new heating system, changes the heat demand.
• Real households differ from the standard one: more people, someone at home all day, or a need for a warmer home all mean more heat.
• Oil, LPG and solid fuel aren’t covered by the price cap, so homes heated with them aren’t included yet.