Air Source Heating

How an air source heat pump works

An air source heat pump moves heat from the outside air into your home. It does not burn fuel. A fan draws outside air over a coil that holds a refrigerant, which absorbs heat even on cold days. A compressor then raises the temperature of that heat.

The system passes the heat into your home through a heat exchanger. The refrigerant then returns outside to collect more heat. The cycle repeats while your heating is on. The heat pump runs on electricity to power the fan and the compressor.

A heat pump usually heats your home at a lower temperature than a gas boiler. It works best when it runs steadily for longer periods. Your installer will set up the controls to suit this way of heating.

Air-to-water and air-to-air systems

There are two main types of air source heat pump. They collect heat the same way but deliver it differently. The right type depends on your home and how you want to heat it. The list below explains the difference.

• Air-to-water. The heat pump warms water for your radiators or underfloor heating. It can also heat a hot water cylinder for taps and showers.
• Air-to-air. The heat pump blows warm air into rooms through indoor units. It does not heat your hot water, so you need a separate way to do that.

The Boiler Upgrade Scheme gives £7,500 for an air-to-water heat pump in England and Wales, or £9,000 when replacing oil or LPG off the gas grid. Air-to-air receives £2,500. The Warm Homes Loan Scheme maximum is £20,000 for air-to-water and £10,000 for air-to-air. You can combine the loan with the grant, which lowers the amount you borrow.

The Boiler Upgrade Scheme covers England and Wales only. Homeowners in Scotland should check advice from Home Energy Scotland, and those in Northern Ireland should check the Energy Saving Trust.

Why insulation and radiators matter

A heat pump delivers heat at a lower temperature, so your home needs to hold that heat well. Good insulation reduces the heat your home loses through walls, lofts and floors. Less heat loss means a smaller heat pump can keep you warm. It also helps each room reach a comfortable temperature.

Radiators need to be the right size for a lower water temperature. A radiator sized for a boiler can be too small for a heat pump. Your installer's heat-loss survey checks every room and shows which radiators need upgrading. Follow these steps before you commit.

1. Check your loft and wall insulation, and fix obvious draughts.
2. Book a heat-loss survey with two or three MCS-certified installers.
3. Ask which radiators or pipes need upgrading, room by room.
4. Confirm where the outdoor unit will sit and how much space it needs.
5. Compare written quotes and check each installer's MCS certification.