Calculator
What Size Heat Pump Do I Need? Heat Pump Sizing Calculator
Use floor area, insulation level, age, bedrooms, climate, and heating emitters to get a broad planning estimate.
Published: 2026-01-01
Last updated: 2026-04-28
Last reviewed: 2026-04-28
Page review status
Written by: HeatWise Home Editorial Team
Reviewed by: Editorial review by HeatWise Home
Review status: Internally reviewed for clarity, source consistency, and calculation assumptions.
Expert review: Not currently externally expert-reviewed.
Last updated: 2026-04-28
Last reviewed: 2026-04-28
Confidence: medium
Sources:
External expert review: HeatWise Home does not currently publish named external expert reviewers. We are working toward adding independent review from qualified retrofit, heating, or building-energy professionals. Until then, users should treat our calculators and guides as educational planning tools and confirm decisions with official sources and qualified installers.
What this sizing estimate can and cannot do
This tool gives you a broad sizing range by combining home size, insulation quality, climate, age, and heating emitters. It helps you understand whether a home may be closer to a smaller or larger system.
It cannot replace a professional room-by-room heat loss survey. Final system selection should always be based on detailed building fabric and emitter calculations.
Helpful next step
See formulas, assumptions, and limits behind each estimate.
Read our calculator methodologyHow the formula works
The calculator applies a rough watts-per-square-metre heat loss factor based on insulation level, then adjusts for property age, climate zone, emitters, and bedroom count.
The result is converted from watts to kW and shown as a range. It is a sense-check, not a professional design load.
Example calculation
Worked example: a 120 m2 home at roughly 60 W per m2 has an estimated peak heat loss near 7.2 kW before survey-level adjustments.
If insulation improves and the estimate falls to 45 W per m2, the rough load becomes 5.4 kW, which can change equipment choice and radiator discussions.
Sizing caveat: this range is a planning aid only; installer design temperature, hot-water demand, and room-by-room emitter performance can shift the final selected kW size.
United Kingdom assumptions
Currency: GBP. Electricity: £0.25 per kWh. Gas: £0.06 per kWh. Heating oil: £0.11 per kWh.
- Planning ranges: Electricity GBP 0.22-0.34 per kWh (Ofgem regional cap spread and available tariffs); Gas GBP 0.05-0.11 per kWh (Ofgem cap benchmark and regional/tariff variation); Heating oil GBP 0.09-0.13 per kWh equivalent (kerosene supplier tracking, delivery-size and season dependent).
- Last checked: 2026-04-28. Confidence: medium.
- Sources: Ofgem energy price cap and market data, GOV.UK Boiler Upgrade Scheme, MCS standards and UK building fabric guidance.
Caveat: prices vary by supplier, tariff, region, standing charge, and usage. Electricity/gas benchmarks align with Ofgem's 1 April to 30 June 2026 cap context (24.67p/kWh electricity and 5.74p/kWh gas GB average, Direct Debit) and broader tariff variation. Heating-oil range uses UK supplier-tracked kerosene pricing converted to kWh-equivalent planning values.
View calculator methodologyEstimated 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.
Sizing FAQs
Helpful next step
Adjust fuel prices, SCOP, grants, and costs using your own numbers.
Estimate your heat pump paybackRelated tools and guides
Methodology and assumptions
Review formulas, SCOP/COP context, fuel price assumptions, and limitations before relying on results.
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