TradeCalculator.co.uk
Hybrid Heat Pump Calculator
Model a hybrid heat pump system for a chosen balance point, and see the cost-optimal balance point for your tariff. Hours split, energy split and annual cost vs gas-only.
Total annual space-heating + hot-water energy (from an MCS heat-loss survey or last year’s gas use)
HP runs above this outdoor temperature, boiler below. The result also suggests a cost-optimal value.
Default 26.11p = Ofgem cap Jul–Sep 2026. Use your actual tariff — a heat-pump tariff can be far lower.
Default 7.33p = Ofgem cap Jul–Sep 2026. Check your own unit rate.
Seasonal efficiency. A modern condensing boiler in good condition ≈ 85–92%.
Seasonal COP from the MCS quote. UK ASHPs ≈ 3.0–4.0; lower (2.5–3.0) at 55 °C flow on existing radiators.
Next up: related pages
How We Calculate This
This calculator splits a year of heating between the heat pump and the gas boiler at your chosen balance point, then prices each part. It also reports the cost-optimal balance point for the prices and SCOP you enter.
How the split works
- Above the balance point: the heat pump runs — usually most heating hours, in milder weather
- Below the balance point: the gas boiler runs, when its higher capacity and lower marginal cost help
- Energy split: mild hours are more numerous but lighter, so the energy split differs from the hours split
- Cost-optimal balance point: the temperature where heat pump heat (electricity price ÷ COP) stops being cheaper than gas heat (gas price ÷ boiler efficiency)
Assumptions and sources
- Heating profile: an indicative UK season of ~2,000 heating hours across seven temperature bins, degree-hour weighted to a 21 °C base and −3 °C design temperature (mean ≈ 7.7 °C). This is an estimate, not a substitute for an MCS heat-loss survey.
- Heat pump COP: modelled to fall with outdoor temperature (more lift in cold weather), centred so the seasonal average equals the SCOP you enter. A UK ASHP is typically SCOP 3.0–4.0, dropping to ~2.5–3.0 at 55 °C flow on existing radiators.
- Default prices: Ofgem price cap for 1 Jul–30 Sep 2026 (electricity 26.11p/kWh, gas 7.33p/kWh, Direct Debit, GB average, incl. VAT). The cap changes every quarter — enter your own tariff.
- Carbon: DESNZ 2026 greenhouse-gas conversion factors — grid electricity ≈ 0.131 kgCO₂e/kWh (generation; the 2025 figure of 0.177 fell ~26% under the 2026 methodology), natural gas 0.183 kgCO₂e/kWh (gross CV). These update each June.
Frequently Asked Questions
A hybrid heat pump combines an ASHP with a gas boiler. The system automatically switches between the two based on outdoor temperature and energy costs. Above the balance point temperature, the heat pump runs (more efficient). Below the balance point, the boiler takes over (higher capacity at low temperatures).
The balance point is the outdoor temperature at which it becomes more cost-effective to switch from the heat pump to the gas boiler. Above it the heat pump runs (high COP, cheap heat); below it the boiler takes over. The cost crossover happens where electricity price ÷ heat pump COP equals gas price ÷ boiler efficiency, so it moves with your tariff and your COP. You set a balance point in this tool, and it also reports the cost-optimal value for the prices and SCOP you enter.
It depends entirely on the electricity-to-gas price ratio and the heat pump COP — there is no guaranteed saving. At the Ofgem cap (Jul–Sep 2026: electricity 26.11p, gas 7.33p, a 3.6:1 ratio) a heat pump at SCOP 3.2 delivers heat at about 8.2p/kWh versus roughly 8.1p/kWh from a 90%-efficient gas boiler, so a gas-led hybrid is close to break-even on running cost. Meaningful savings (often 15–30%) appear mainly on a low-rate or heat-pump-specific electricity tariff, or with a higher SCOP. Always run your own figures — this tool will show a negative number honestly when the hybrid costs more than gas alone.
A hybrid system has lower installation costs (smaller HP, no radiator upgrades needed) and can be cheaper to run when gas is relatively cheap compared to electricity. However, a well-designed full heat pump system with appropriate radiators can achieve lower long-term costs and greater carbon savings.
Usually not. The beauty of a hybrid system is that the gas boiler handles the coldest days when radiator output would be most compromised. The heat pump runs mainly in milder weather when existing radiators can cope. This avoids the radiator upgrade cost of a full heat pump system.
Related Calculators
Was this calculator helpful?
Last updated: June 2026
Verified against UK standards · estimates only, confirm with your supplier.