What Size Boiler Do I Need?

A UK starting size in kW from radiator count, bathrooms, and boiler type. A Gas Safe engineer should confirm this with a heat-loss calculation before you buy.

Boiler type

Combi kW is driven by hot water as well as heating

Bedrooms 3

Radiators 10

Baths and showers 1

Suggested size
25 kW

Typical band

24–28 kW

Get a boiler quote Boiler types

This is not a heat-loss calculation. UK bands like these are used for a first look only. Insulation, ceiling height, water pressure, and how many outlets run at once all change the right kW. Oversizing a combi for DHW is common; heating-only and system boilers are usually smaller for the same house because hot water comes from a cylinder.