Boiler Replacement Calculator
Instantly estimate your ideal boiler size (kW), potential carbon savings, and replacement urgency. Free, accurate tool for UK homeowners.
Check Your Boiler Requirements
Enter your property details and current boiler age to get an instant evaluation of your required boiler size, potential efficiency gains, and replacement urgency.
Property Details
Enter your home specifications to calculate requirements
System Evaluation
Calculated heating metrics and recommendations
Boiler Size Guidelines
Standard boiler output (kW) recommendations based on UK property types to help you understand your heating requirements.
| Property Type | Bedrooms | Recommended Boiler Size (kW) | Ideal For |
|---|---|---|---|
| Flat / Apartment | 1 – 2 | 24 – 28 kW | 1 Bathroom, low hot water demand |
| Terraced House | 2 – 3 | 28 – 32 kW | 1 – 2 Bathrooms, medium demand |
| Semi-Detached | 3 – 4 | 32 – 36 kW | 2 Bathrooms, higher heating demand |
| Detached House | 4 – 5+ | 36 – 45+ kW | 2+ Bathrooms, high heating demand |
Boiler Replacement FAQ
Everything you need to know about boiler sizing, efficiency, and replacement timelines.
Boiler size is measured in kilowatts (kW). A small flat with one bathroom typically needs 24-28 kW, while a large detached house with multiple bathrooms may require 35-45 kW. The ideal size depends on your property’s heat loss, number of radiators, and hot water demand.
Most modern boilers have a lifespan of 10 to 15 years. If your boiler is over 10 years old, requires frequent repairs, makes unusual noises, or struggles to heat your home evenly, it is highly recommended to start planning for a replacement.
Yes. Older boilers often operate at 70-80% efficiency, meaning a significant portion of energy is wasted. Modern A-rated condensing boilers operate at 90%+ efficiency, which can noticeably reduce both your carbon footprint and energy consumption.
A combi boiler provides hot water on demand without a storage tank, ideal for smaller homes. A system boiler uses a hot water cylinder, making it better for homes with higher hot water demand. A regular (conventional) boiler requires both a cylinder and a cold water tank, typically found in older properties with low water pressure.