The useful starting point
A heat pump can use less purchased energy while still costing more or less to run, depending on your unit rates and seasonal efficiency. Compare the cost of delivering the same amount of heat.
Keep useful heat separate from fuel
A gas bill measures fuel bought. A heating system delivers useful heat after losses. If you assume a boiler’s seasonal efficiency is 90%, 10,000 kWh of gas delivers about 9,000 kWh of heat in that model.
For a heat pump, a seasonal coefficient of performance (SCOP) of 3.5 means the model delivers 3.5 units of heat for each unit of electricity across the season. It is different from a single test-point COP. Ask the designer for a seasonal estimate relevant to your system and flow temperature.
A transparent annual comparison
Consider an illustrative home needing 12,000 kWh of useful heat. Assume electricity at 27p/kWh, gas at 7.5p/kWh, a heat-pump SCOP of 3.5 and a boiler efficiency of 90%.
| System | Purchased energy | Annual energy cost |
|---|---|---|
| Heat pump | 12,000 ÷ 3.5 = about 3,429 kWh | About £926 |
| Gas boiler | 12,000 ÷ 0.90 = about 13,333 kWh | £1,000 |
In this example the heat pump’s energy cost is about £74 lower. These rates and assumptions are examples, not a current tariff recommendation. Change them in the heating cost tool.
Find the break-even efficiency
For energy costs alone, the break-even SCOP is the electricity rate multiplied by boiler efficiency, divided by the gas rate. With the example rates, that is 27 × 0.90 ÷ 7.5 = 3.24.
A system performing above that seasonal figure would have a lower modelled energy cost; below it, a higher one. The result changes when rates change. This is why a blanket claim that every heat pump is cheaper to run is unhelpful.
Account for the rest of the decision
The calculation excludes installation, servicing, finance and standing charges. Gas standing charges are only avoided if the gas account can close; a gas hob or another gas appliance may mean it remains. A new installation may also require cylinder space, radiator changes and electrical work.
Time-of-use electricity tariffs require realistic weighting. Applying the cheapest overnight rate to every unit used for heating exaggerates the saving unless the system genuinely buys all those units in that period.
Ask for a design you can review
- Room-by-room heat loss and proposed emitter sizes.
- Design flow temperature and expected seasonal efficiency.
- Hot-water arrangements and any additional electric heating assumptions.
- Control strategy, commissioning and support.
- Full installed cost and separately identified funding.
Use the installation cost guide and funding guide alongside the running-cost comparison.
Published information supports your research. Your installer should confirm the exact product, suitability, scope and terms for your property.
Suggest a correction ↗Your next useful step
Put the information to work.
Take the questions that matter to your project, explore the numbers and decide what to ask next.