Free tool
Boiler Sizing Calculator
Find the boiler size (kW) your home is likely to need — then we’ll sanity-check it properly and design the best setup for comfort, efficiency and hot water performance.
Instant estimate
Your home
Exposure and heat loss vary by property type (detached/bungalow often need more output).
Insulation affects heat loss, which impacts required heating output.
Used as a practical cross-check alongside floor area.
This often changes the best solution (e.g. system + cylinder vs simply upsizing).
Estimates only. Final sizing depends on heat loss, hot water usage, controls and radiator outputs.
Your recommendation
Recommended size
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Suggested range
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Heating driver
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Hot water focus
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Tip: Right-sizing matters — oversized boilers can cycle more and waste energy.
Want a proper design, not a guess?
We’ll confirm the best boiler and setup for your property and hot water usage — then optimise for comfort, efficiency and reliability.
- Right-sizing: avoid oversizing, reduce cycling, improve efficiency.
- Comfort: quicker warm-up, fewer cold spots, better balance across radiators.
- Hot water performance: realistic flow-rate expectations, simultaneous showers, cylinder sizing & recovery.
- System design: zoning, controls, pipework checks, radiator outputs, future-proofing for extensions/bathrooms.
Good to know: we’ll include your calculator summary so our engineer already has the basics.
