Air source heat pump
Plain English. Practical detail. UK context.
An air source heat pump uses electricity to move heat from outside air into a building. In an air-to-water system it supplies water-based heating and usually a hot water cylinder. An air-to-air system distributes warmth through indoor air units. These arrangements meet different needs and should not be treated as identical products.
Last reviewed: (editorial review against the public sources listed below).
How it is designed for a home
A useful proposal starts with room-by-room heat loss, suitable emitters and the intended operating temperatures. Radiators may need changing, but replacing every radiator is not an automatic rule. The installer should assess pipework, hot water demand, available cylinder space, electrical supply and the outdoor unit position. Access for maintenance, airflow, condensate or defrost water and the relationship to neighbours all affect the design, even when the unit physically fits.
Using it on a job
Heat pumps often work well with lower flow temperatures and steadier operation than a boiler system designed around short hot bursts. Controls need to match the building and occupants rather than copy old timer settings unquestioningly. Ask for the design flow temperature, heat loss assumptions and expected seasonal performance basis in writing. A single laboratory COP figure is not a promise of whole-system performance through a British winter. Weather compensation changes water temperature as outdoor conditions change.
Common mistakes
Oversizing, poor emitter selection, restrictive pipework and badly explained controls can all undermine an otherwise capable appliance. A heat pump is not proof that insulation is irrelevant, but an older house is not automatically unsuitable either. Avoid any claim that running costs will definitely fall: tariffs, previous fuel, system design and operation matter. The outdoor unit should not be boxed in for appearance without considering airflow, clearances, noise and the manufacturer’s requirements.
Alternatives, rules and handover
Ground source systems, air-to-air heating and conventional systems may suit different constraints. Planning, building regulations, electrical work and refrigerant requirements must be assessed for the actual design and UK nation. MCS certification may be relevant to funding or scheme eligibility, but eligibility must be checked rather than assumed. A good handover includes commissioning records, control settings, maintenance needs and a practical explanation of hot water operation. Ask who will provide technical support after installation.
Frequently asked questions
Does it work in cold weather?
Heat pumps are designed to extract heat in cold conditions, but capacity and efficiency vary. The system must be sized for the design conditions.
Will I need a hot water cylinder?
Usually for a standard air-to-water installation providing domestic hot water, though other system arrangements exist.
Is a heat pump guaranteed to cut bills?
No. The existing system, tariff, design and operation affect the comparison.
Will a heat pump work with radiators?
It can, but each radiator must provide adequate output at the proposed operating temperatures. A room-by-room assessment establishes which emitters can remain and which need changes.
Sources and further reading
Public sources and further reading. Sources checked: 8 November 2026. Consult the original for details and later changes.