This calculator estimates heat demand by property type and insulation level, then divides by a conservative SCOP to find ASHP electricity consumption. Running cost is ASHP electricity × assumed unit rate. Current-fuel cost uses published unit rates and typical boiler/heater efficiencies. All figures are indicative — they assume average occupancy and are not a substitute for a proper MCS heat-loss survey.

Heat demand assumptions (kWh/year, space + hot water):

Key assumptions:

• ASHP SCOP: 3.0 (conservative; well-insulated homes on a heat-pump tariff can reach 3.2–3.5+). SCOP = Seasonal Coefficient of Performance — units of heat delivered per unit of electricity consumed.
• Electricity unit rate: ~25p/kWh (Ofgem price cap era, Q2 2025). Heat-pump-specific tariffs (e.g. Octopus Cosy/Heat Pump) can reduce this to ~20–22p/kWh — improving economics further.
• Gas unit rate: ~7p/kWh, boiler efficiency 88% → effective cost ~8p/kWh delivered heat.
• Oil unit rate: ~8p/kWh (kerosene at ~65p/litre), boiler efficiency 90% → effective cost ~8.9p/kWh.
• LPG unit rate: ~11p/kWh, boiler efficiency 90% → effective cost ~12.2p/kWh.
• Electric storage heaters: ~22p/kWh Economy 7 night rate; assumed efficiency ~100% (direct electric) — effective cost 22p/kWh delivered heat.
• BUS grant: £7,500 off an ASHP under the Boiler Upgrade Scheme (England & Wales, current as of 2025 — confirm eligibility at gov.uk). Not available in Scotland (separate scheme) or Northern Ireland.
• Installed cost: Typical ASHP installation £9,000–£14,000 before grant (indicative; varies significantly by property, heat emitter compatibility and access). Net after £7,500 BUS grant: ~£1,500–£6,500.
• Payback: Net install cost ÷ annual saving. Shown only when running costs are lower than current fuel. For gas-heated homes, savings are often modest — payback may be long or not shown.

An honest note on gas vs heat pump: If your home is on mains gas, a heat pump will often cost roughly similar to run — sometimes a little more, sometimes a little less — because today's electricity-to-gas price ratio (~3.5×) offsets much of the efficiency gain. The economics improve materially if: (1) you add insulation first; (2) you switch to a heat-pump electricity tariff; (3) you add solar PV. Vs oil, LPG, and electric storage heaters, the savings are usually clear. This calculator shows ranges to reflect this honestly.

Sources: Energy Saving Trust — Heat Pumps, Ofgem energy price cap, gov.uk — Boiler Upgrade Scheme, MCS — Microgeneration Certification Scheme (SCOP methodology).

This calculator is for guidance only. Actual running costs depend on your specific property, heat emitters, hot water usage, occupancy, and energy tariff. An MCS-accredited heat-loss survey is required before any heat pump installation.

Most UK homes can have an air source heat pump fitted, but the economics and comfort are best when:

• Insulation is good: A well-insulated home needs less heat, so a smaller (cheaper) heat pump can do the job at a higher SCOP. If insulation is poor, improving it first is usually cost-effective.
• You have larger radiators or underfloor heating: Heat pumps run at lower flow temperatures (45–55°C) than gas boilers (65–75°C). Larger-surface-area radiators or UFH work best. Radiator upgrades can be added to the installation.
• You have outdoor space for the unit: An ASHP unit is roughly the size of an air-conditioning unit. Planning permission is usually not required under permitted development.
• You're replacing oil, LPG or electric heating: The savings case is strongest here.

EcoHome UK will assess your property's suitability as part of a free, no-obligation survey.