Air source heat pumps explained
How an air-to-water heat pump replaces a boiler, how it is sized, what it costs and how to make it cheap to run.
What it replaces
An air-to-water heat pump replaces your boiler. It heats water for your radiators or underfloor heating and for a hot water cylinder. It works on the same refrigerant cycle as air conditioning, but delivers the heat into water instead of air.
Sizing starts with a heat loss survey
A good installer measures every room and calculates how much heat your home loses on the coldest days. That number decides the size of the pump and whether any radiators need to be bigger. Be wary of a quote that names a size without a room-by-room calculation.
Low and slow is cheapest
Heat pumps are most efficient at low flow temperatures, around 35 to 45 °C. The home is kept at a steady temperature all day rather than blasted twice a day. Bigger radiators, good insulation and correct controls are what make the running costs low.
Typical costs
Installed prices usually fall between £9,000 and £15,000 before any grant, depending on size, radiator changes and whether a new cylinder is needed. In England and Wales the Boiler Upgrade Scheme takes £7,500 off, or £9,000 if you are switching from oil.
Space you will need
- Outdoor space for the unit, with airflow around it.
- A cylinder cupboard if you currently have a combi boiler.
- A valid EPC for the grant.