Boiler Replacement Cost by House Size
Your property size is one of the biggest factors in choosing the right boiler and estimating cost. Larger homes need more powerful boilers with higher kW output, which cost more to buy and run.
1-2 Bedroom Flat
40-65 m²
Cost Range
£1,800–£3,500
Recommended Type
Combi
Boiler Size
24-28 kW
Annual Running Cost
£650/yr
2-3 Bedroom Terrace
65-85 m²
Cost Range
£2,200–£4,000
Recommended Type
Combi
Boiler Size
28-32 kW
Annual Running Cost
£800/yr
3-4 Bedroom Semi
85-120 m²
Cost Range
£2,500–£5,000
Recommended Type
Combi or System
Boiler Size
30-35 kW
Annual Running Cost
£950/yr
4-5 Bedroom Detached
120-200 m²
Cost Range
£3,500–£6,500
Recommended Type
System
Boiler Size
35-40 kW
Annual Running Cost
£1200/yr
5+ Bedroom Large Home
200+ m²
Cost Range
£4,000–£8,000
Recommended Type
System or Regular
Boiler Size
40+ kW
Annual Running Cost
£1500/yr
How to Size Your Boiler
Getting the right boiler size is crucial. Too small and your home won't be warm enough; too large and you'll waste energy and money. The key factors are:
- Number of radiators — each radiator typically needs 1.5 kW of output
- Number of bathrooms — multiple bathrooms need a higher flow rate (system boiler recommended for 2+ bathrooms)
- Property insulation — poorly insulated homes need higher output
- Mains water pressure — affects combi boiler performance; low pressure may need a system boiler
A qualified Gas Safe engineer will perform a heat loss calculation for your property to determine the exact kW output you need. Always get this done before choosing a boiler.
Worried about the cost?
Explore finance options to spread the cost, or check if you qualify for a government grant.