All you need to know about heat pumps

Heat pumps are the main way UK homes are moving off fossil-fuel heating — but there's a lot of noise and misinformation about them. This guide answers the questions homeowners actually ask, in plain English, so you can decide whether one's right for your home. When you're ready, the cost calculator gives you an instant estimate.

What is an air source heat pump?

An air source heat pump is a unit that sits outside your home and extracts heat from the outside air, even when it's cold, then concentrates it and uses it to heat your radiators, underfloor heating and hot water. It runs on electricity but moves far more heat energy than the electricity it uses, which is why it's efficient. Think of it as a fridge working in reverse.

There are two main types in UK homes: air source (the common, lower-cost option that takes heat from the air) and ground source (which takes heat from buried pipes and costs more to install). Most of this site focuses on air source, since it suits the majority of homes.

How does a heat pump work?

It draws in outside air across a coil containing a refrigerant. The refrigerant absorbs heat and evaporates, then a compressor squeezes it to raise its temperature. That heat passes through a heat exchanger into your home's water circuit for heating and hot water. The cooled refrigerant expands and the cycle repeats. No fuel is burned in your home.

Because it moves heat rather than creating it by burning fuel, it delivers more energy than it consumes — the source of its efficiency.

What temperature do heat pumps run at?

Heat pumps run your radiators cooler than a gas boiler — typically a flow temperature of 35–50°C rather than 60–70°C. They make up for the lower temperature by running steadily for longer and using correctly sized radiators, giving even, constant warmth rather than short hot blasts.

Are heat pumps noisy?

Modern units are quiet — usually around 40–60 decibels at close range, similar to a fridge or a quiet conversation, and quieter still a few metres away. Sensible siting away from bedroom windows keeps them unobtrusive. There are also limits on how loud they can be near a neighbour's property.

Do heat pumps work in winter?

Yes. Air source heat pumps are designed to extract heat from air well below freezing and are used across Scandinavia in far colder winters than the UK's. Efficiency drops a little on the coldest days, but a properly sized system keeps a home warm through a British winter.

Heat pump myths explained

Common myths: that they don't work in cold weather (they do), that they can't heat an old house (they can, with the right design), that they're always noisy (modern ones aren't), and that they'll slash a gas home's bills (against mains gas, running costs are often roughly neutral — the honest wins are the grant, comfort and carbon).

We're a referral service, so we'd rather tell you the honest version up front: if you're on mains gas, switch for comfort, carbon and the grant — not for a dramatic bill cut. If you're on oil, LPG or electric heating, the running-cost savings are real. See our heat pump vs gas comparison.

How efficient are heat pumps?

Efficiency is measured by COP or SCOP — the ratio of heat out to electricity in. A good air source heat pump has a seasonal efficiency (SCOP) of around 3 to 4, meaning it delivers three to four units of heat for every unit of electricity. A gas boiler, by contrast, is always below 1 because it loses energy in combustion.

Heat pump lifespan

A well-installed, serviced air source heat pump typically lasts around 15–20 years — longer than a typical gas boiler. The outdoor unit is built for permanent outdoor use, and the hot water cylinder and other components have similar long lifespans.

Heat pump maintenance

Very little. An annual check by a qualified engineer to inspect refrigerant, electrics and the system's settings, plus keeping the outdoor unit clear of leaves and debris. There's no annual gas safety inspection because nothing is burned. Maintenance costs are modest — see our costs page for figures.

Can a heat pump replace my boiler?

For most homes, yes — a heat pump fully replaces a gas, oil or LPG boiler for both heating and hot water. The installer carries out a heat-loss survey to size the system and check your radiators and pipework. Some homes need a few larger radiators; very few need major work. Use the eligibility guide to check your situation.

Keep reading

• What a heat pump costs — installation, running and maintenance costs explained.
• Can I get a heat pump? — eligibility for flats, old houses, solid walls and more.
• What installation involves — timings, radiators, planning permission.
• The £7,500 Boiler Upgrade Scheme grant — who qualifies and how it works.