Heat Pump Size Calculator
Estimate an indicative heat pump output from your design heat requirement.
Indicative heat pump output
8.8kW
Rough estimate only. Use a professional heat-loss assessment and MCS-compliant design for equipment selection.
v1.0 · Reviewed September 2026
How this is worked out
The design heat requirement is increased by the sizing margin you enter.
Worked example
- 8 kW design heat requirement
- 10% margin
8 × 1.10
8.8 kW
Assumptions and limits
- Starts from a design heat requirement you already have. It does not calculate your home's heat loss, and guessing that figure makes the answer meaningless.
- Heat pump output falls as outdoor temperature drops, so manufacturers quote output at a design condition such as −2°C flow at 45°C. Compare like for like.
- Oversizing causes cycling and poor efficiency, so a large margin is not a safe default.
- An MCS-certified installer must carry out a room-by-room heat loss survey for a compliant design, and for grant eligibility.