Heat pumps attract a lot of noise, some of it overcooked in both directions. Stripped of the jargon, a heat pump is a proven, efficient way to heat a home with electricity. Whether one is right for you comes down mostly to your house and how it is run, not the technology itself. This guide explains how a heat pump works, what the efficiency numbers actually mean, how it can beat a gas boiler on energy even though electricity costs more per unit, and the honest conditions under which it disappoints.
The short answer. A heat pump works like a fridge in reverse. It uses a little electricity to gather warmth from the outside air or ground and concentrate it to a useful temperature for your radiators and hot water. Because it moves existing heat rather than making it, it delivers about 3 to 4 units of heat per unit of electricity (a SCOP of 3 to 4). That efficiency is why it can beat a gas boiler on energy used. Whether it beats a boiler on running cost is closer, because electricity costs about 26.11p per kWh against 7.33p for gas.
Heat moved, not made
A heat pump does not burn anything and does not glow like an electric bar fire. It works like a fridge running in reverse. A fridge takes heat out of its inside and dumps it into your kitchen; a heat pump takes heat out of the outside air or ground and pumps it into your home.
The trick is that even cold air contains heat. Air at 2C still holds plenty of energy compared with the very low temperatures a refrigerant boils at. The pump evaporates a refrigerant using that outside warmth, compresses it (which raises its temperature), and passes the now-hot refrigerant through a heat exchanger that warms the water for your radiators and cylinder. The compressor is the only part that uses much electricity.
Because the pump is moving heat that already exists rather than creating it from scratch, it can deliver several units of warmth for each unit of electricity it draws. That is the whole reason it can compete with, and on energy beat, a gas boiler that burns fuel at best around 90 percent efficient.
What the efficiency numbers mean
Two figures get quoted, and they are worth understanding because they decide whether a heat pump saves you money.
- COP (coefficient of performance) is the instantaneous ratio of heat out to electricity in, measured at set conditions. A COP of 3.5 means 3.5 kWh of heat for every 1 kWh of electricity.
- SCOP (seasonal COP) is the average across a whole heating season, including the cold days when the pump works hardest. This is the honest, real-world number. A well-installed air source heat pump in a suitable house typically achieves a SCOP of around 3 to 4.
SCOP matters because it falls as you ask the pump for hotter water. Run it at a low flow temperature, around 35C to 45C, and the SCOP stays high. Push it to 60C to feed undersized radiators and the SCOP drops towards 2.5, which is where the running-cost complaints come from. The whole game is keeping that number high, which means low flow temperatures, which means a house and radiators that can be kept warm without hot water.
Will it cost less to run than a gas boiler?
This is the question that actually matters, and it is closer than either the fans or the critics admit. The sum is fuel price divided by efficiency.
| System | Fuel price | Efficiency | Cost per useful kWh of heat |
|---|---|---|---|
| Gas condensing boiler | 7.33p/kWh gas | ~90% | 8.1p |
| Heat pump, SCOP 2.5 (poor) | 26.11p/kWh elec | 250% | 10.4p |
| Heat pump, SCOP 3.5 (good) | 26.11p/kWh elec | 350% | 7.5p |
| Heat pump, SCOP 4.0 (excellent) | 26.11p/kWh elec | 400% | 6.5p |
At 26.11p/kWh electricity and 7.33p/kWh gas, Ofgem cap July to September 2026. Worked examples; check your own tariff.
So a heat pump running at a good SCOP of 3.5 or better undercuts a gas boiler per unit of heat. One stuck at a poor SCOP of 2.5 costs more than gas. The dividing line is efficiency, which is set by the house, the radiators and the flow temperature. A time-of-use electricity tariff with a cheap overnight rate can tip the sum further in the pump's favour. The full comparison is in the heat pump versus gas boiler running cost guide.
It likes low and slow
A heat pump is happiest producing a gentle, steady warmth rather than blasting out very hot water on demand. This is a genuine change of habit for anyone used to a gas boiler, and it is where most disappointment comes from.
A boiler can be left off all day and then fired hard to warm a cold house in an hour. A heat pump cannot do that economically. It runs at lower flow temperatures and prefers to keep the house at a steady temperature across the whole day, trickling in heat as the house loses it. Run that way it sits at a high SCOP and the house stays comfortable. Run it in short hot bursts and the SCOP collapses.
That is why it pairs best with larger radiators or underfloor heating, which give off enough heat at a low water temperature, and with a home that holds its warmth. The same low-and-slow logic is why insulation and draught-proofing come first.
This also changes how you control the heating day to day. With a boiler, many people fire it for an hour morning and evening. With a heat pump, the cheapest approach in a well-insulated home is often to set a steady, modest temperature and leave it, letting the pump trickle heat in as the house loses it. Frequent deep setbacks force the pump to claw the house back up from cold, which it does inefficiently. A smart thermostat set up for low, steady running suits a pump far better than the on-off habits of a gas system.
The house makes or breaks it
The technology is not really the variable. The building is. In a well-insulated home with suitable radiators, a heat pump runs efficiently and cheaply and keeps the place warm all day. In a cold, draughty, poorly insulated house heated in short hot bursts, the same pump struggles and the bills disappoint.
So the advice is always the same, and it is the same lesson as the rest of this site with the stakes raised: improve the fabric first. Loft insulation, cavity wall insulation or solid wall insulation where it applies, draught-proofing and good glazing all cut how much heat the pump has to supply, which lets it run at a lower flow temperature and a higher SCOP. A leaky house forces the pump to work hard and hot, which is exactly where the cost and the complaints live.
A good installer will do a proper heat-loss survey of your house rather than guessing, and size the radiators and pump to run at a low flow temperature. That survey is worth more than the brand of pump.
Is a heat pump for you?
A heat pump makes the most sense if your home is reasonably insulated, or you are willing to improve it, if you have somewhere outside for the unit, and if you can live with running the heating gently across the day rather than in spikes. Grants help: the Boiler Upgrade Scheme offers a fixed grant towards the cost in England and Wales, which changes the payback considerably.
It is a bigger decision than any single tweak on this site, so treat it as a long-term step taken once the cheap fabric improvements are done, not before. If you are weighing the two types, the ground source versus air source guide covers that choice, and if you want the running-cost detail against your current boiler, the heat pump versus gas boiler running cost page works it through. For the wider context, the main home heating hub ties it all together, and smart thermostats help run a pump in the steady way it likes.