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Size doesn't matter? When it comes to boilers, it really does!

If you're scouring the web for a new combi boiler then you'll need an idea of what boiler size is suitable for your home - Small, Medium or Large won't be much use here, unfortunately.

The size of a combi boiler, or more accurately, it's power, is measured in Kilowatts (kW). The actual size of the boiler unit itself will rarely change in correlation with the kW. However, this can sometimes be the case for particularly powerful boilers so do check the unit dimensions to make sure it's going to fit where you plan to keep it.

Boiler Kilowatts tend to come in three approximate sizing brackets; 23kW - 27kW, 28kW - 33kW and 34kW - 42kW.

Use the table below as an approximate guide to what your home will need:

Property Type Bedrooms Bathrooms Radiators Average kW
Flat 1-2 10 10 or less 26
House 2-3 1 15 or less 26
House 3-4 1-2 15+ 28
House 4+ 2 20+ 34
House 4+ 2+ 20+ 42

The above table is a rough estimate to arm you with some knowledge before you begin comparing quotes, but you should always take advantage of the expert opinion of a qualified heating engineer. You can call any Heatable Pro - free of charge


The price of the boiler will ascend in accordance with its operating power so overshooting what you need to get a Niagara Falls-like water pressure rate, will cost you!... the recommended Kilowattage should do just fine.

Combi boilers are fantastic for their hot water on demand and efficiency, but it’s worth keeping in mind that if you live in a multi-bathroom home, a combi boiler may not be the ideal solution – the water pressure may be significantly affected. If this does apply to you, we would recommend looking into having a system boiler fitted which has a separate water tank – allowing larger quantities of hot water to be heated and distributed to multiple water demand points.

The above advice and table contents are to be used as a guide only and Heatable recommends you seek the advice of a qualified and Gas Safe registered engineer before making any boiler purchase.

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Respresentative finance example: Purchase price: £1,695, Deposit: £847.50, Credit: £847.50, Total repayable: 2.452.30, Duration: 120 months, Rate: 9.9% APR, Cost of credit: £496.11

[1] Price based on a like for like combi swap in a 2 bed, 1 bathroom terraced home with a standard flue

[*] Installation dates are subject to installer availability