Energy prices, grant rules, and installation costs change frequently. The figures on this page are estimates for planning only. Always check current supplier rates, installer quotes, and official government grant rules before making decisions.
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Sizing starts with heat loss
A heat pump should be sized to meet the home's design heat loss during cold conditions. Floor area can give a rough starting point, but it cannot replace a room-by-room assessment.
Coastal exposure, older construction, attic insulation, windows, draughts, and emitter sizing all affect the result.
Example rough range
A 120 m2 home with average insulation might roughly fall around 6 to 9 kW depending on age, exposure, ventilation, and radiators. A better insulated home of the same size may need less.
Use the calculator for a broad check only. Final equipment selection should come from a qualified survey and design.
United Kingdom assumptions
Currency: GBP. Electricity: Check current official sources. Gas: Check current official sources. Heating oil: Check current official sources.
Last reviewed: 2026-04-27. Confidence: medium. Prices are not pre-filled because supplier tariffs and price caps change. Enter your current unit rates from a bill.
Estimated heat loss range
9.7 to 11.9 kW
Suggested heat pump size range
9.2 to 13.1 kW
Important warning
This is only a broad planning estimate and is not a replacement for a professional room-by-room heat loss survey.
Suggested next steps
Book a professional heat loss survey before choosing equipment. Ask installers to confirm emitter suitability at lower flow temperatures. Review insulation and draught proofing before final sizing.
Calculators on this site are estimates only. Always get a professional heat loss survey and verify current grant rules, tariffs, and product suitability before making purchase decisions.
Sizing FAQs
Only roughly. Floor area helps provide a starting estimate, but accurate sizing depends on fabric losses, airtightness, ventilation, glazing, and local climate.