Published 12 March 2026
We get the same conversation almost every week: 'Our last heat pump worked, but it ran flat out and the bill was huge.' Almost always, the unit was the wrong size for the room - or sized for the floor area only, ignoring everything else that matters.
Square metres are a bad proxy
Two 30m² rooms can need very different units. A south-facing bedroom with single glazing, a high ceiling and uninsulated walls demands far more capacity than a sunny north-facing lounge with double glazing and modern insulation.
When sizing, we look at room volume, glazing, sun exposure, insulation levels, ceiling height, infiltration, and how the room is actually used. Floor area is one input - not the answer.
Bigger isn't safer
It's tempting to 'go bigger to be sure.' But oversized heat pumps cycle on and off frequently, never reaching the slow, steady operation they're most efficient at. The result: drafts, noise, higher running costs and a shorter lifespan.
How we size yours
Our free in-home assessment takes about an hour. We measure rooms properly, look at how the home behaves, and recommend a unit (or units) sized to the way you actually live. No upsell pressure.