Methodology
The data, formulas, and editorial process behind every calculator and guide on HeatPumpCalcs.co.uk. Built by an MCS-certified engineer, reviewed every quarter, transparent about every assumption.
Editorial principles
- Independence. We accept no payment from any heat pump brand, installer, or energy supplier. No affiliate fees on any link on this site (as of 2026-07-01). When that changes, we will disclose it on this page first.
- Transparency. Every figure is sourced. Where we estimate, we say so and show our working.
- UK focus. Every calculator uses UK climate, tariff, and product data. We don't recycle US or EU averages.
- Conservative bias. Where ranges exist, we show realistic mid-range UK figures, not best-case marketing claims.
- Quarterly refresh. Calculators are re-checked every 3 months against Ofgem cap, Octopus tariffs, BUS scheme rules, and MCS pricing.
How our calculators work
Heat Pump Cost Calculator
Inputs: home type, number of bedrooms, age, fuel type, region.
Method: Property-type-based heat loss multiplier (W/m²) × estimated floor area gives kW capacity required. The kW size maps to a 2026 MCS installer median quote for that size, sourced from MCS UK published average install costs and cross-checked with three of our own quotes per kW band. BUS grant of £7,500 is deducted from gross cost.
Heat Pump Size Calculator
Inputs: property age, bedrooms, insulation level.
Method: BS EN 12831 simplified room-based heat loss methodology. Uses U-values from BRE Domestic Energy Fact File for typical UK construction. Returns kW capacity at -2°C design outdoor / 21°C indoor for England (regional adjustment for Scotland/Wales/NI based on Met Office winter design temperatures).
Air Source Heat Pump Cost Calculator
Same methodology as Heat Pump Cost Calculator but ASHP-specific, with separate cost curves for R290 vs R32 unit choices.
Heat Pump Savings Calculator
Inputs: current annual heating bill, fuel type, tariff.
Method: Converts current heating fuel cost to kWh delivered (using fuel-specific calorific values and boiler efficiency assumptions). Multiplies by current heat pump SCOP (3.2 default, user-adjustable). Multiplies by user's electricity tariff (Ofgem cap default 26.35p/kWh; Cosy default 12.5p cheap / 24p standard / 36p peak weighted average).
Boiler Upgrade Scheme Calculator
Inputs: current heating system, MCS installer chosen yes/no, EPC status.
Method: BUS scheme eligibility rules per Ofgem published criteria (March 2026 version). Returns £7,500 if all eligibility met; flags blockers otherwise.
Heat Pump vs Gas Boiler
Inputs: home size, current annual gas consumption, tariff choice.
Method: gas cost (per Ofgem cap, current 6.99p/kWh) vs heat pump cost (per chosen tariff and SCOP). Returns 20-year cumulative cost differential including BUS grant and assumed gas boiler replacement at year 12.
Octopus Heat Pump Cost Calculator
Inputs: home size, optimisation level (none / partial / full Cosy schedule).
Method: Octopus Cosy quarterly rate schedule (4 cheap windows daily averaged) × estimated kWh demand × scheduling efficiency factor (no opt: 100% peak weighted, partial: 70% peak, full: 40% peak).
Hybrid Heat Pump Cost Calculator
Inputs: home size, existing boiler type, design split (% load to heat pump vs gas).
Method: Cost-weighted blend of heat pump and gas boiler running costs at user-specified split. BUS grant for the heat pump component applies.
Heat loss calculations
Our property-type heat loss assumptions, used in cost and sizing calculators:
| Property type | Heat loss W/m² | Total heat loss (typical floor area) |
|---|---|---|
| New build 2010+ | 45 | 4-6 kW (1-2 bed) / 6-9 kW (3-4 bed) |
| 1980-2010 well insulated | 55 | 5-7 kW (1-2 bed) / 8-11 kW (3-4 bed) |
| 1950-1980 cavity wall | 70 | 6-9 kW (1-2 bed) / 10-14 kW (3-4 bed) |
| Pre-1950 solid wall | 85 | 8-11 kW (1-2 bed) / 12-17 kW (3-4 bed) |
| Listed building / Victorian | 95 | 10-13 kW (1-2 bed) / 14-20 kW (3-4 bed) |
These W/m² figures are derived from BRE Domestic Energy Fact File 2024 averages, cross-referenced with installer survey data. Individual homes will vary ±20% depending on actual fabric, occupant behaviour, and exposure.
SCOP assumptions
Default SCOPs used in calculators:
- Air source heat pump: 3.2 (UK installation average per MCS published data)
- Ground source heat pump: 4.0
- Hybrid heat pump (heat pump portion): 3.0
Users can override these in the calculator interface. We display "Excellent" (3.5+), "Good" (3.0-3.4), "OK" (2.7-3.0), "Poor" (under 2.7) bands. See SCOP Explained.
Tariff data
Default tariff figures (refreshed quarterly):
- Ofgem standard cap (Apr-Jun 2026): 26.35p/kWh electricity, 6.99p/kWh gas
- Octopus Cosy (2026): 12.5p cheap windows (4-7am, 1-4pm, 10pm-12am), 24p standard, 36p peak (4-7pm)
- Octopus Intelligent Go: 7p/kWh overnight (6 hours), 26p standard
When rates change quarterly, we update all calculators within 14 days of the new rate confirmation by Ofgem or supplier.
Cost data — install pricing
Median UK installed cost for 8 kW air source heat pump (2026):
- Tier 1 brand (Mitsubishi, Vaillant, Daikin): £14,500-£16,500 gross, £7,000-£9,000 net of BUS
- Tier 2 brand (Grant, Samsung, LG): £12,000-£14,500 gross, £4,500-£7,000 net of BUS
- Ground source heat pump: £20,000-£28,000 gross, £12,500-£20,500 net of BUS
Pricing sourced from: MCS published average install cost data, 3-quote benchmarks from author's own East-of-England customer base, MCS installer association surveys, and verified online MCS firm pricing.
Editorial process
- Topic chosen based on UK heat pump buyer search demand (Google Search Console + Semrush data)
- Outline drafted to cover 5 standard sections (Overview, Costs, Process, Comparisons, FAQ)
- Research using primary sources: MCS, Ofgem, Historic England, manufacturer technical data
- Draft written by James Thornton
- Editorial review for accuracy and clarity
- Published with date stamp and review schedule
- Quarterly refresh checks for any rule changes, price updates, or data refinements
Corrections policy
If you find an error in any calculator or guide, please email corrections at heatpumpcalcs.co.uk. Material corrections are made within 7 days and noted on the affected page with a dated update line. Non-material updates (tariff rates, BUS scheme tweaks) happen quarterly without separate notification.
What we DON'T do
- We don't run sponsored content. Brand mentions are based on technical merit, not payment.
- We don't accept affiliate fees (current as of 2026-07-01). Status updates will be disclosed on this page.
- We don't sell or share visitor data beyond standard analytics (Google Analytics 4).
- We don't recommend specific local installers — we recommend you verify any installer at mcscertified.com.
For data sources, see our Sources page. For the people behind this site, see About.