What happens during a heat pump survey?
Short answer
A good heat pump survey measures your home room by room and calculates how much heat it loses on a cold day. The installer then uses that figure to size the heat pump and each radiator. This design stage matters because an oversized heat pump can be less efficient, while an undersized one may struggle in cold weather.
Last checked 24 September 2026 · 2 sources
What does the engineer measure?
Expect measurements of walls, windows, floors and ceilings, together with the construction type of each part of the building.
The aim is to estimate heat loss at a low outdoor temperature. In the source interview, the installer used roughly -2°C to -3°C as an example design condition.
A proper survey should also record existing radiators, pipework, hot-water arrangements, electrical supply and possible locations for the outdoor unit.
Why is room-by-room heat loss so important?
Different rooms lose heat at different rates.
A large room with several outside walls may need much more heat than a small internal room. The survey converts those differences into a heat requirement for each space.
That lets the designer choose radiators that can meet demand at a sensible flow temperature.
Flow temperature is the temperature of the water leaving the heat pump and travelling to your radiators. Lower flow temperatures generally help heat pumps run more efficiently.
Is oversizing safer?
Not necessarily.
The source interview says undersizing is relatively uncommon, while oversizing is a more frequent design problem. An oversized unit can cost more, take up more space and operate less efficiently if it cycles too often.
A good installer should therefore show you the calculated heat loss rather than simply fitting the next size up “to be safe”.
How long does a heat pump survey take?
The visit itself may take a few hours, but the design work continues afterwards.
The installer in our source interview said a fully manual survey and design for a larger home could take around three working days in total, including radiator design. That is one installer’s estimate, not a fixed industry standard.
What should I do next?
Before accepting a quote, ask for:
- the whole-home heat-loss figure;
- the room-by-room heat-loss calculation;
- the proposed heat pump size;
- the design flow temperature;
- the proposed radiator sizes;
- an explanation of any radiator or pipework changes.
Sources
- Source interview with Heat Geek installer, heat-load calculation and radiator-sizing sections.
- MCS heat pump design standards, referenced by Boiler Upgrade Scheme requirements.
Last checked: 24 September 2026