The short answer
A heat pump can cost less to run than a gas boiler, about the same, or more. Which one you get depends on two numbers: how efficiently the heat pump turns electricity into heat over a year, and how much more a unit of electricity costs you than a unit of gas. This guide shows how to put the two together, using illustrative figures. It does not promise a saving, because only your own tariff and house can tell you that.
COP and SCOP in plain words
COP (coefficient of performance) is how many units of heat a heat pump delivers for each unit of electricity it uses, at one moment. A COP of 3 means 1 kWh of electricity gives 3 kWh of heat. A kWh is the unit on your energy bill.
SCOP (seasonal coefficient of performance) is the same idea averaged across a whole heating year, cold snaps included. SCOP is the number that matters for your bills.
A gas boiler works the other way round. A modern condensing boiler turns most of the gas it burns into heat, but never more than 100%. A heat pump can deliver several times more heat than the electricity it uses, because it moves heat from outside rather than making it.
The price ratio
Electricity per kWh usually costs several times more than gas per kWh. Divide your electricity unit rate by your gas unit rate and you get your price ratio. You will find both rates on your bill or in your supplier app.
Here is the rule of thumb that falls out of the arithmetic:
A heat pump costs less to run than a gas boiler when its SCOP is higher than your price ratio multiplied by your boiler’s efficiency.
Illustrative arithmetic
The figures below are illustrative only. They are round numbers chosen to show the method, not current prices and not a forecast. Use your own tariff.
Assume a house needs 10,000 kWh of heat a year for heating and hot water. Assume gas costs 6p per kWh, electricity costs 24p per kWh (a price ratio of 4), and the old boiler is 90% efficient.
Gas boiler: 10,000 ÷ 0.9 = about 11,100 kWh of gas. At 6p, that is about £667 a year.
| Heat pump SCOP (illustrative) | Electricity used | Cost at 24p per kWh | Compared with £667 gas |
|---|---|---|---|
| 2.5 | 4,000 kWh | £960 | More expensive |
| 3.0 | 3,333 kWh | £800 | More expensive |
| 3.6 | 2,778 kWh | £667 | About the same |
| 4.0 | 2,500 kWh | £600 | Cheaper |
In this example the break even point is a SCOP of 3.6, which is the price ratio of 4 multiplied by the boiler efficiency of 0.9. Change either number and the break even point moves:
- If your price ratio were 3 instead of 4, break even would fall to a SCOP of 2.7.
- If you moved to a tariff with cheaper electricity for heating, the heat pump side of the table would shrink.
- If your old boiler is less efficient than 90%, the gas side grows and the heat pump looks better.
These sums ignore standing charges, servicing and any other appliances. Use them to understand your own numbers before you rely on any saving.
Work out your own figures
- Find your gas unit rate and electricity unit rate on your latest bill.
- Divide electricity by gas to get your price ratio.
- Find your yearly gas use in kWh on your annual statement.
- Ask an MCS-certified installer for the expected SCOP of the system they design for your house.
- Multiply your price ratio by your boiler’s efficiency as a decimal (0.9 for 90%, for example). If the expected SCOP is comfortably above that figure, the heat pump is likely to cost less to run.
What raises SCOP
The design of the system matters as much as the heat pump itself.
- Low flow temperature. Flow temperature is the temperature of the water sent to the radiators. The lower it can be while keeping rooms warm, the higher the SCOP. Bigger radiators allow lower flow temperatures. See radiators for heat pumps.
- Correct sizing. A unit sized from a proper heat loss calculation runs steadily. An oversized one cycles on and off. See what size heat pump do I need.
- Insulation and draughts. Less heat lost means less work for the heat pump.
- Sensible controls. Most heat pumps run best kept on steadily rather than switched on and off in short bursts.
When gas may stay cheaper
If your house loses heat fast, needs high flow temperatures to stay warm, and you cannot change radiators or insulate, the SCOP may land below your break even point. In that case a heat pump could cost more to run, and a new boiler may be the better call for now. It is better to know that before you buy. Our installation cost guide covers the upfront side of the decision.
Common questions
Is a heat pump cheaper to run than a gas boiler?
It can be, but it is not automatic. It depends on how efficiently your heat pump runs over the year and how much your electricity costs compared with gas. Work out your own ratio from your bills, using the method on this page, before relying on any savings figure.
What is a good SCOP for a heat pump?
The higher the better, because SCOP is how many units of heat you get for each unit of electricity across a year. Well designed systems running at low flow temperatures achieve higher figures than poorly designed ones. Ask your installer for the expected SCOP for your house in writing.
Do heat pump tariffs help?
They can. Some suppliers offer tariffs with cheaper electricity at certain times or for heat pump owners. A lower electricity price shrinks the price ratio, which is the single biggest lever on running costs after the design itself.
Will I save the gas standing charge?
If you remove gas entirely, including the hob, you can close the gas account and stop paying its standing charge. If you keep a gas hob or a hybrid boiler, you keep paying it.