Enter your property type, floor area, bedrooms, bathrooms, and radiators, along with insulation level, hot water usage, and boiler type to get your recommended boiler size, plus heating output, hot water output, and target efficiency — so you're not paying for more boiler than you need.
Recommended Boiler Size
--
Heating Output Required
--
Hot Water Output Required
--
Target Efficiency
--
For a typical 3-bedroom house with average insulation, you'll usually need a boiler between 24-30kW. The exact size depends on your floor area, number of radiators, and hot water demand.
Combi boilers provide heating and hot water on demand without storage tanks. System boilers require a hot water cylinder but no cold water tank. Conventional boilers need both hot water cylinder and cold water storage tank in the loft.
Yes, an oversized boiler will cycle on and off frequently, reducing efficiency and increasing running costs. It's important to size your boiler correctly to match your home's heating demand.
Count all radiators and heated towel rails in your home. Each standard single radiator typically requires 1-2kW, while double radiators need 2-3kW depending on size and room requirements.
Yes, better insulation reduces heat loss, meaning you need less boiler output. Well-insulated modern homes typically need 30-50% less heating capacity than poorly insulated older properties.
Heat pumps typically need to be sized 1.5-2 times larger than gas boilers due to lower flow temperatures. However, they're much more efficient, often achieving 300-400% efficiency ratings.
While calculators provide good estimates, a Gas Safe registered engineer should perform a proper heat loss calculation for your home to ensure accurate sizing and optimal efficiency.
Hot water demand significantly impacts combi boiler sizing. Homes with multiple bathrooms or high hot water usage need larger boilers (30-35kW) to maintain adequate flow rates to multiple outlets.