What Size Boiler Do I Need?
Answer 3 quick questions about your London home and get an instant boiler size recommendation — then see the exact fixed-price package that fits.
How Boiler Sizing Actually Works
Boiler size depends mainly on bathrooms, not bedrooms. A combi boiler heats water on demand rather than storing it, so the number of taps and showers that might run at once matters more than how many people sleep in the house. A one bathroom flat is usually fine on a 24kW to 27kW combi. A two bathroom family house typically needs 28kW to 34kW. Homes with three or more bathrooms often need 35kW or above, or a system boiler with a cylinder instead of a combi, since no combi can comfortably serve three simultaneous showers.
Why Get This Right Before You Buy
Weak pressure at peak times
A boiler that's too small struggles when two taps run at once — showers go cold, pressure drops.
Wasted money, short-cycling
A boiler that's too big for the property cycles on and off more often, wearing out faster and wasting gas.
Efficient and reliable
Matched to your actual bathroom demand, a correctly sized boiler runs efficiently for its full 10+ year lifespan.
We confirm before you order
This calculator gives a reliable starting point — a quick free call confirms it against your actual pipework and gas supply.
Boiler Size Calculator — Common Questions
What size boiler do I need for my London home?
Boiler size depends mainly on the number of bathrooms in your home, not just bedrooms. A one bathroom flat usually needs a 24kW to 27kW combi boiler, a two bathroom house usually needs 28kW to 34kW, and homes with three or more bathrooms often need 35kW or above, or a system boiler with a cylinder.
Why do bathrooms matter more than bedrooms for boiler size?
A combi boiler heats hot water on demand. The more bathrooms that might run simultaneously, the higher the flow rate the boiler needs to deliver without a drop in pressure or temperature. Bedroom count affects heating load but bathroom count affects hot water demand, which is usually the bigger factor in combi sizing.
Is this boiler size calculator accurate enough to buy from?
This calculator gives a reliable starting range based on property type, bedrooms and bathrooms, which covers most London homes. For an exact recommendation we always confirm your existing pipework, gas supply and water pressure with a quick call before you order, at no charge.
What if I have a large house with three or more bathrooms?
Homes with three or more bathrooms often exceed what a standard combi boiler can comfortably supply during peak simultaneous use. In these cases we usually recommend a system boiler paired with an unvented hot water cylinder, which stores hot water rather than heating it instantly.
Our Boiler Services
Once you know your size, here's everything else we do.
Boiler Installation In Your Area
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