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Free calculator

Use this calculator to

  • Estimate annual electricity use for an air source heat pump from heating demand and SCOP
  • Compare heat pump running cost against a gas boiler at your own contract rates
  • Test how SCOP changes the economics before committing to a retrofit
  • Model boiler efficiency from 50 to 100 percent to reflect older plant

Heat Pump COP & Running Cost Calculator

Compare air source heat pump running costs against a gas boiler for UK homes.

kWh/yr

Typical UK semi-detached: 10,000–15,000 kWh/yr heating.

COP

Air source typical: 2.5–3.5 COP (seasonal average SCOP).

p/kWh
p/kWh
%
Annual Cost Comparison

Formulas

  • Heat pump electricity used = Heating demand / COP
  • Heat pump annual cost = Electricity used × tariff
  • Gas used = Heating demand / boiler efficiency
  • Gas annual cost = Gas used × gas tariff
  • Annual saving = Gas cost − Heat pump cost

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Replacing a 30-year-old gas boiler with a commercial heat pump used to be an ESG line item. With Climate Change Levy on gas falling, electricity carbon factors declining, and the gap between unit prices narrowing in the right tariff structures, it is increasingly a finance question. A 100 kW heat pump running at a seasonal COP of 3.2 delivers heat at roughly a third of the electricity input, and whether that beats gas on running cost depends on the spread between p/kWh gas and p/kWh power on the actual contracts the site is on.

The number that matters is annual £, not COP in isolation. A school with a 350,000 kWh gas demand pays roughly £21,000 at 6 p/kWh. The equivalent heat pump load at COP 3 needs around 117,000 kWh of power. At 25 p/kWh that is £29,250, at 18 p/kWh it is £21,060, and at 14 p/kWh it is £16,380. The contract terms, the time-of-use shape, and any onsite PV change the answer materially. Plus there is the Boiler Upgrade Scheme grant and the carbon reporting angle for SECR-listed organisations.

Purely Energy advises clients planning electrification on the contract design that makes the engineering case stand up. That includes time-of-use tariff selection for heat pump duty cycles, half-hourly metering on the new circuit, capacity headroom on the existing MIC, and how non-commodity charges land on a load that now runs all winter rather than just the gas meter ticking over. The kit is only one part of the answer. Multi-site operators in particular need a portfolio view, because the COP that works at the Midlands site will look different at the Glasgow site once the heating degree-day profile is added in, and the right tariff for one will be wrong for the other.

Common questions

What do COP and SCOP mean?

COP, coefficient of performance, is the ratio of heat delivered to electricity consumed at a single test condition: a COP of 3.0 means 3 kWh of heat per 1 kWh of electricity. SCOP is the seasonal average across a whole heating year, including cold snaps and defrost cycles, so it is the figure to use for annual cost estimates. Air source units in the UK typically achieve a SCOP between 2.5 and 3.5.

How much electricity will a heat pump use per year?

Divide your annual heat demand by the SCOP. A building needing 12,000 kWh of heat with a SCOP of 3.0 uses about 4,000 kWh of electricity. The same demand met by a 90 percent efficient gas boiler burns roughly 13,300 kWh of gas. That difference in units consumed is the whole economic argument, and it is why the electricity-to-gas price ratio decides the outcome.

Is a heat pump cheaper to run than a gas boiler?

It depends on your unit rates, not on a universal answer. The break-even condition is simple: a heat pump is cheaper when your electricity price divided by your gas price is below the SCOP divided by the boiler efficiency. At SCOP 3.0 against a 90 percent boiler, that threshold ratio is about 3.3. Enter your own contract rates above and the calculator does the comparison for you.

What SCOP should I assume for my building?

Flow temperature is the biggest factor. Underfloor heating or generously sized radiators running at 35 to 45°C support a SCOP of 3.0 to 3.5; a retrofit pushing 55°C through the original radiators may manage 2.5 to 2.8. Manufacturer SCOP figures are quoted at defined flow temperatures, so match the figure to your emitter design rather than taking the brochure headline.

How do I find my annual heating demand in kWh?

For a gas-heated building, take annual gas kWh from your bills and multiply by the boiler efficiency, since some input is lost up the flue: 14,000 kWh of gas through a 90 percent boiler is about 12,600 kWh of useful heat. Businesses on half-hourly metering can separate heating from baseload by comparing winter and summer consumption. An EPC or a heat-loss survey gives a more formal figure for sizing.

Related calculators

The conversions that procurement and engineering use alongside this one.

Heat Pump COP & Running Cost Calculator | UK | Purely Energy