By Lewis Wiggins, Gas Safe registered engineer · Updated
As a rough guide, combi boilers of around 24 to 30kW suit flats and homes with one bathroom, 30 to 35kW suit homes with two bathrooms, and larger homes with three or more bathrooms usually need a system boiler. Your installer should confirm the size based on your home and hot water use.
Why boiler size matters
A boiler that is too small will struggle to deliver enough hot water, while one that is too big can waste energy. The right size depends on how much hot water you use at once and how much heat your home needs.
Typical combi boiler sizes
- Flat or small home, 1 bathroom: around 24 to 30kW
- Medium home, 2 bathrooms: around 30 to 35kW
- Larger home: 35kW or more, or consider a system boiler
System and regular boilers
For system and regular boilers, the size is based mainly on your heating needs, because hot water is stored in a cylinder. Many homes need somewhere between 15 and 30kW.
Get it sized properly
Our online quote asks about bedrooms, bathrooms and your current boiler to recommend a size, and Lewis checks the details before installation.