ASHP explainer

What is an air source heat pump?

An air source heat pump takes heat from outside air and upgrades it for space heating and, in many systems, hot water. The real question is not just what it is. It is whether the property, emitters, and survey assumptions suit the route properly.

Air source survey overview ASHP survey packs

Basics

An ASHP is a low-temperature heating system, not just a new box outside

How it works

The outdoor unit extracts heat from external air, even when it feels cold outside. That heat is upgraded and used to feed a wet heating system such as radiators or underfloor heating.

What it connects to

Most domestic ASHP systems are tied to emitters, pipework, and often a hot-water cylinder. That means the success of the install depends on more than just outdoor-unit placement.

What it is not

It is not the same as an air-to-air system. Air-to-air routes deliver warm or cool air directly through indoor units instead of feeding a wet emitter network.

Suitability

The result depends on heat loss, emitters, hot water, siting, and electrical reality

Fabric and demand

Heat-loss assumptions need to be credible
U-value defaults can change the design conversation fast
Poor evidence creates false confidence early

Emitters and hot water

Existing radiators may or may not be enough
Cylinder layout and plant-room reality still matter
The system route has to fit how the home is actually heated

Outside and electrical

Outdoor-unit siting is never just a sketch problem
Noise, route length, access, and neighbour context matter
Electrical context can make a simple idea more complex on site

Use the next route

Pick the page that matches the decision you are making now

Air source survey overview ASHP vs air-to-air ASHP efficiency guide ASHP calculator guide Heat loss calculations