Boiler Size Calculator
Find the right boiler size (kW or BTU) for your home’s heating and hot water needs. Get an accurate estimate based on your home’s specifications.
Your Recommended Boiler Size
Your home requires a medium-sized boiler for optimal efficiency.
Based on your inputs, we recommend a boiler with at least 24 kW output. Adding a 10-15% safety margin gives the recommended size of 24 kW.
Note: If you choose a significantly larger boiler, you risk short-cycling and lower efficiency. If you choose a smaller one, you may not meet your heating and hot water demands.
Suggested Boiler Sizes
| Boiler Size | Typical Home Size | Radiators | Bathrooms |
|---|
Why Boiler Size Matters
Choosing the right boiler size is crucial for efficiency, comfort, and cost savings. An oversized boiler will cycle on and off frequently (short-cycling), reducing efficiency and increasing wear. An undersized boiler will struggle to meet your heating and hot water demands, especially during cold weather.
How We Calculate
Our calculator uses industry-standard heat loss calculations based on:
- Home size and layout: Larger homes require more heating capacity
- Insulation quality: Well-insulated homes lose less heat
- Climate: Colder regions require more heating capacity
- Hot water demand: Based on number of bathrooms and occupants
- Radiators: More radiators require higher heating capacity
We then add a 10-15% safety margin to ensure your boiler can handle peak demand.
Next Steps
Use this estimate as a starting point when consulting with heating engineers. They will perform a detailed heat loss calculation to confirm the right size for your specific home. Always get multiple quotes before making a decision.
Frequently Asked Questions
For a typical 3-bedroom house (approx. 1000-1500 sq ft / 90-140 sq m), you’ll typically need a boiler between 24-30 kW, depending on insulation, climate, and hot water needs.
An oversized boiler will short-cycle (turn on and off frequently), which reduces efficiency, increases wear and tear, and can lead to higher energy bills. It may also struggle to maintain consistent temperatures.
Yes! Improving insulation reduces heat loss, which means you may be able to use a smaller, more efficient boiler. Consider an energy audit to identify the most cost-effective insulation upgrades.
kW (kilowatts) and BTU/h (British Thermal Units per hour) are both units of power. 1 kW is approximately 3,412 BTU/h. The UK and EU typically use kW, while the US uses BTU/h for boiler ratings.
Combi boilers need to be sized to meet both heating and instant hot water demands. They’re often slightly larger than system or regular boilers for the same heating load to ensure adequate hot water flow.