52 Likes Comments Comment
Like if this guide is helpful

What size boiler do i need ?

A good starting point is the boiler you already have installed.

If you are happy with the temperature of the house and hot water then its probably sized correctly, so a direct replacement would be advised.

Another way to check the heat required by your system would be to total all your radiator output then add the hot water requirements.


You Have a 3 bedroom house with 10 radiators and a hot water tank as follows

Lounge 1200x600 DP = 1.5kw Lounge 600x600 SP = 0.7kw

Din/Room 1200x600 DP = 1.5kw

Kitchen 800x600 DP = 1.0kw

Hall 1000x600 SP = 0.8kw

Bed 1 1100x600 SP = 0.9kw

Bed 2 100x600 SP = 0.8kw

Bed 3 600x600 SP = 0.6kw

Bathroom 500x600 SP = 0.5kw

Landing 700x600 SP = 0.65kw

Allow 4kw for your hot water tank

Total 12.95kw or 44,185 Btu's

If you round up to the next boiler size that would be a 50,000 Btu boiler. Most modern condensing boilers are fully modulating, they match the output to exactly what is required.

That means from cold your boiler will send out 50,000btu. When the house reaches temperature it may only need to send out 20,000btu to maintain that temperature thus saving on gas used.

For Help with correct sizing email us your radiator sizes and we will work out which boiler is right for you.

Explore more guides