Boiler Size Calculator (UK)
Construction & Home ImprovementEstimate the combi boiler size, in kilowatts, recommended for a UK home based on bedroom and bathroom count.
Recommended Boiler Size
Approximate minimum recommended combi boiler output, in kilowatts, for this size of home.
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Odeh Ahwal0people find this calculator helpful
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Saved
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Construction & Home Improvement calculators
Frequently Asked Questions
How accurate is this estimate?
This uses a commonly cited rough sizing table based on bedroom and bathroom count, converged from multiple UK boiler-guide sources. Real boiler sizing also depends on insulation quality, number of radiators, and simultaneous hot water demand, so treat this as a starting estimate rather than a final specification. A proper heat loss survey, or a plumber using the heat loss calculator on this site, gives a far more accurate figure.
Why does bathroom count matter for a combi boiler?
A combi boiler heats hot water on demand rather than storing it, so a home with more bathrooms needing simultaneous hot water draws a higher output to avoid pressure or temperature drops when more than one tap or shower runs at once.
What if I have more than 20 radiators or more than 2 bathrooms?
Most UK heating guides recommend moving beyond a simple combi boiler at that point, either to a system boiler with a separate hot water cylinder, or a professional heat loss survey, since a combi boiler alone may struggle to keep up.
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