UK Heat Pump Calculator

How this calculator works

You enter property type, age, floor area, insulation level, glazing, current fuel and boiler efficiency, yearly heating demand in kWh and the heat pump type. Your current running cost is the heat demand divided by the boiler efficiency you pick, multiplied by an assumed price per kWh for your fuel. The heat pump running cost is the same demand divided by a fixed seasonal efficiency (COP) of 3 for air source or 4 for ground source, multiplied by an assumed electricity price. The difference, plus a small fixed maintenance adjustment, is the annual saving. The hybrid option uses the air source figure.

Installation cost is a fixed price by heat pump type and floor area band, plus extras if you tick new radiators or a hot water cylinder. If the grant box is ticked, £7,500 comes off, the Boiler Upgrade Scheme rate for air and ground source heat pumps in England and Wales. Some off-gas homes can get more until 31 March 2027, which the calculator ignores. Payback is the net cost divided by the annual saving. The suitability score adds and subtracts points for insulation, glazing, current fuel, property age and size, so it is a rule of thumb, not a survey.

Fuel prices, efficiencies and costs are assumed values written into the page, not live tariffs, and carbon figures use the UK government's 2026 conversion factors per kWh. An installer would size a system from a room-by-room heat loss calculation. The result is an estimate, not approval under the Boiler Upgrade Scheme or ECO4.

Read the air source heat pump grant guide for the scheme rules, or check your eligibility for ECO4.

Worked example

Example inputs, which are also the calculator's starting values: a semi-detached house with 150 m² of heated floor area (the 100 to 200 m² band), gas heating with an old non-condensing boiler (65%), 12,000 kWh of heat a year, an air source heat pump, no radiator or cylinder extras, the £7,500 grant box ticked, average insulation, double glazing and a build date of 1950 to 1990.

1. Current gas cost: 12,000 kWh ÷ 0.65 = 18,461.5 kWh of gas, × £0.073 per kWh = £1,347.69 a year.
2. Heat pump cost: 12,000 kWh ÷ COP 3.0 = 4,000 kWh of electricity, × £0.285 per kWh = £1,140 a year.
3. Running saving: £1,347.69 − £1,140 = £207.69. The calculator then applies a fixed −£50 maintenance adjustment for gas homes, giving £157.69, shown as £158 a year.
4. Installation: £10,000 (air source, 100 to 200 m²) − £7,500 grant = £2,500 net.
5. Payback: £2,500 ÷ £157.69 = 15.9 years.
6. Carbon: gas 12,000 × 0.182 = 2,184 kg, heat pump 4,000 × 0.131 = 524 kg. The difference is 1,660 kg, shown as 1.7 tonnes a year (76% lower).
7. Suitability score: 35 base + 15 (double glazing) + 10 (floor area under 200 m²) = 60, rated Good.

The result depends heavily on the boiler efficiency you pick. With the 92% condensing option, the same house's gas cost is £952.17, which is below the £1,140 heat pump cost, so the calculator shows a negative saving of −£238 a year and N/A for payback.

How this is calculated and sources

The £7,500 is the Boiler Upgrade Scheme grant named in the calculator's code, which the page says applies in England and Wales, so check GOV.UK for current rules. The carbon factors (0.182 for gas, 0.131 for electricity) are labelled in the code as the UK Government GHG Conversion Factors 2026 (DESNZ). The fuel prices, the COP of 3.0, the boiler efficiencies, installation costs, the £50 adjustment and the suitability points have no source in the code, so they are assumptions used by this calculator. The output is an estimate, not a quote or a grant approval.