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Knowledge Centre
What Affects Whether a Property Suits an Air Source Heat Pump?
A heat pump's success depends on the building's heat loss, emitter sizing, hot-water setup and outdoor unit location — which is why a proper survey beats a generic rule of thumb.
Heat loss and insulation
A heat pump works best in a property that does not leak heat quickly. The better the insulation, draught-proofing and glazing, the lower the required flow temperature and the more efficient the system. A fabric-first approach — improving the building envelope before or alongside the heat pump — usually gives the best result.
Existing radiator sizing
Gas boilers often run at flow temperatures of 60–70°C or more. Heat pumps work most efficiently at lower flow temperatures, commonly 35–55°C. Because radiators emit less heat at lower temperatures, the existing radiators may be too small to heat the rooms on the coldest days. Upgrading to larger radiators or underfloor heating is often needed.
Hot water cylinder requirements
Most air source heat pumps heat a hot water cylinder rather than providing instant hot water. The cylinder needs to be the right volume for the household, and there must be a suitable location for it. Some properties lack the space, which can affect whether a heat pump is practical.
Outdoor unit siting and noise
The outdoor unit needs free airflow and a stable base. It also produces condensate that must drain away safely. Noise levels vary by model and installation, so siting should respect neighbouring properties and any planning or permitted-development limits.
Why a proper heat-loss survey matters
A room-by-room heat-loss calculation measures how much heat each space needs and at what flow temperature. It is the difference between a system that is correctly sized and one that is under- or over-specified. Generic rules of thumb cannot account for the construction, orientation and usage of an individual property.
Related service and funding
If you are considering a project, read more about our Air Source Heat Pump design and installation service. For current grant routes, see Finance & Funding.
Last reviewed
20 August 2026
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