Home Heat Loss Calculator | Homestead Project

Home Heat Loss Calculator

Use our free home heat loss calculator to estimate how much heating your property needs on the coldest days of the year. Enter details for the rooms in your home, including their size, insulation and windows, to estimate your peak heat loss in kW. Your result can help you understand the heating capacity your home requires and provide a starting point when considering a heat pump.

Home heating calculator

How much heat does your home need on a very cold day?

Start with a quick estimate in a few minutes. Then add more detail only if you want a tighter result.

Default design temperature −5°C You can change this

Step 1

Tell us the basics

No room-by-room measuring is needed for the first estimate.

⌂

Use your Energy Performance Certificate (EPC)

For now, please look up your property manually on the official GOV.UK EPC service, then copy the relevant information into this calculator.

Look up my property on GOV.UK

Automatic property lookup is coming soon. In a future version, you will be able to enter your address or postcode and have available EPC details filled in automatically.

Property name optional Postcode optional Total floor area

m²

Usually shown on your EPC. Property type Approximate age Number of storeys you heat Average indoor temperature

°C

Cold-day outdoor temperature

°C

−5°C is the default. Later we can suggest this automatically from postcode.

Step 2

Your quick estimate

This gives a useful starting range without making you measure every room.

Basic estimate

Estimated peak heat loss — at −5°C outdoors

Reasonable range — Use the refine step to narrow this down.

What this means

Walls & glazing—

Roof / ceiling—

Floor—

Air leakage / ventilation—

Don't buy a heat pump from this number alone. A final heat-pump design should use a proper room-by-room heat-loss calculation and the manufacturer's output at the required outdoor and water-flow temperatures.

What should I do next? Improve the estimate for a better result, or continue now to compare heating technologies.

Continue to Heating System Recommender →

Step 3 · Optional

Refine the estimate

Only answer what you know. The calculator keeps sensible defaults for everything else.

Refined estimate

Building height & shape

Measure the wall height once for each level — not every room.

Know the outside footprint dimensions? Optional. This improves wall-area accuracy.

Building length

Building width

Insulation & construction

External walls Windows Loft / roof insulation Ground floor How draughty does it feel? Approximate window area

Optional EPC cross-check

EPC space-heating demand optional

kWh/yr

This is used as a sense-check, not as the peak heat-loss calculation. EPC rating optional

Refined peak heat-loss estimate —

Indicative range —

Next step

Next: choose the best heating system for your home

Carry your calculated peak heat loss into the next questionnaire and rank the most suitable heat-pump technologies for your priorities.

Compare heating systems →

Want to continue another day? Create a free account and your home details can be saved.

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How the estimate works

The calculator estimates design heat loss from fabric losses (walls, glazing, roof and floor) plus ventilation/infiltration losses. The quick mode estimates geometry from floor area, storeys and property type. The refine mode lets the user replace those assumptions with better information.

It is intended to be a homeowner planning tool. Final heat-pump selection should still be checked with a room-by-room professional design calculation.

What does the home heat loss calculator tell me?

Your home’s heat loss is the amount of heat that needs to be replaced by your heating system to maintain a comfortable indoor temperature. The colder it becomes outside, the faster your home loses heat.

The calculator estimates your property’s peak heat loss in kilowatts (kW). This gives you an indication of how powerful a heating system needs to be during cold weather.

Why is heat loss important when choosing a heat pump?

Correct sizing is particularly important for heat pumps. A system that is too small may struggle to maintain the required temperature during very cold weather, while unnecessarily oversizing a system can increase installation costs and may reduce efficiency.

Your calculated heat requirement can therefore be used as a starting point when comparing air-source, ground-source and other heat-pump systems.

How accurate is the calculator?

This calculator is intended to provide an initial estimate rather than replace a professional heat-loss survey. Actual heat loss depends on factors including construction materials, insulation, air leakage, windows, doors and local weather conditions.

For a heat-pump installation, a qualified installer should carry out a detailed room-by-room heat-loss calculation before selecting the final system.

What should I do with my result?

Once you have calculated your home’s heating requirement, you can use our Heat Pump Recommender to compare different types of heat pumps and find systems that may be suitable for your property.

You can also learn about air-to-water heat pumps, air-to-air heat pumps, ground-source heat pumps and community heat-pump systems in our heat-pump guides.