Heat pumps

How it works

It works like a fridge in reverse. A fluid picks up heat from outside, even on a cold day, a compressor raises its temperature, and that heat goes into the water in your radiators and hot water cylinder. Because it moves heat rather than making it, a heat pump gives out more energy as heat than it uses in electricity. Over a year a well-installed air source heat pump typically delivers around three units of heat for each unit of electricity.

Most UK installations are air source: a unit outside the house, connected to the heating pipes inside. Ground source heat pumps collect heat through pipes buried in the garden or in a borehole. They cost more to install and need the space. Air-to-air heat pumps blow warm air into rooms like an air conditioner and don't heat water.

Older and colder homes

The government's Electrification of Heat trial fitted heat pumps in around 750 British homes of every age and type, from Victorian terraces to flats, and found no type of home that couldn't have one. Some needed insulation or larger radiators first. A survey of your home is what tells you which.

Radiators and flow temperature

A heat pump runs most efficiently when the water in the radiators is cooler than a boiler would make it, so it runs for longer at a lower temperature. Rooms stay at a steady temperature instead of warming up twice a day. Some rooms may need a larger radiator to stay warm at that lower temperature. Many won't.

An installer works this out with a room-by-room heat loss calculation, which also sets the size of the heat pump. Underfloor heating suits heat pumps well. Insulating first shrinks the heat pump you need, but you don't have to finish it before switching: see insulation and draughts.

Hot water

A heat pump heats a hot water cylinder, a tank usually kept in an airing cupboard or utility room. If you have a combi boiler you have no cylinder now, so you'll need room for one, roughly the footprint of a small fridge and taller. Compact heat batteries are an alternative for homes with no space. The AR visualiser can place a true-size cylinder in the cupboard you have in mind.

Noise and where the unit goes

The outdoor unit has a fan and a compressor. Modern units are quiet a few metres away, but where it goes matters: away from bedroom windows, and not in a narrow gap or enclosed corner where sound bounces around. Installers have to show the unit will meet a noise limit at your neighbours' nearest window.

You can hear a real one with the sound simulator and see how big it is in your garden with the AR visualiser.

Planning permission

In England most air source and ground source heat pumps are permitted development and don't need planning permission, provided they meet conditions on size, position and noise. Listed buildings and conservation areas have extra rules, and Scotland, Wales and Northern Ireland each have their own. Your installer should check, and your council's planning team can confirm. The Planning Portal has the rules for England.

Running costs

Whether a heat pump costs more or less to run than your boiler depends mainly on how well it is designed and set up, and on the price of electricity compared with gas or oil. Tariffs made for heat pumps, and tariffs with cheaper hours, make a large difference: see tariffs, meters and your supply. If you disconnect the gas entirely you also stop paying the gas standing charge.

The savings calculator estimates it for your home at current prices, and paying for it covers the grants.

When to switch

The easiest time is while your boiler still works, so there is time to get quotes and fit it properly. The boiler escape plan works out a sensible time for your home and what to do before then.