How they work
A heat pump moves heat rather than generating it: refrigerant absorbs low-grade heat from outside air or the ground, a compressor raises its temperature, and a heat exchanger delivers it to your heating and hot water. The efficiency measure is the SCOP (seasonal coefficient of performance) — typically 3–4, meaning 3–4 kWh of heat per kWh of electricity. No flue, no fossil fuel, no combustion.
In the SAP calculation
With SAP 10’s electricity carbon factor down at 0.233 kgCO₂/kWh, a heat pump at SCOP 3+ beats a gas boiler on carbon by a wide margin — usually the single biggest lever available for a SAP pass. And with the Future Homes Standard removing fossil-fuel heating from new homes from 2027, heat pumps are becoming the default rather than the alternative.
They suit low-temperature systems best: underfloor heating or generously sized radiators, in a well-insulated, airtight dwelling — which new builds are by definition.
Air source or ground source?
ASHP — an external unit extracting heat from air. Cheaper, simpler, fits almost any plot; SCOP slightly lower and drops in the coldest weather.
GSHP — extracts heat from the ground via buried loops or boreholes. Higher SCOP and steadier year-round, but significantly higher install cost and needs land or drilling. Best on larger plots, larger houses, or shared-loop developments.
We model both options in SAP as standard — ask us which earns its cost on your project.