Combination Boiler vs System Boiler
Compare these two popular boiler types to find which suits your home best
Combination Boiler
All-in-one boiler providing heating and hot water on demand without the need for separate tanks or cylinders.
System Boiler
Boiler that works with a separate hot water cylinder, ideal for homes with multiple bathrooms.
Key Statistics
Advantages Comparison
Combination Boiler Advantages
Space-saving design
No need for separate hot water cylinder or cold water tank, freeing up valuable cupboard space.
Instant hot water
Hot water is heated on demand, so you never run out and don't waste energy heating a tank.
Lower installation costs
Simpler installation with fewer components means lower upfront costs.
Energy efficient
Only heats water when needed, reducing energy waste.
Good water pressure
Water comes directly from the mains, providing strong pressure.
Cheaper to run
No heat loss from storing hot water, making running costs lower.
System Boiler Advantages
Multiple taps simultaneously
Can supply hot water to multiple outlets at the same time without pressure drop.
Compatible with solar panels
Works well with solar thermal systems for added efficiency.
Constant hot water supply
Cylinder stores hot water, ensuring supply during high demand periods.
Good for larger homes
Ideal for properties with 3+ bedrooms and multiple bathrooms.
More space than Regular
Doesn't require a cold water tank in the loft, saving some space.
Reliable performance
Proven technology with consistent hot water delivery.
Disadvantages Comparison
Combination Boiler Disadvantages
Limited hot water flow rate
Water flow reduces if multiple taps are used simultaneously.
Not ideal for multiple bathrooms
Struggles to supply enough hot water when demand is high.
Performance depends on mains pressure
Poor water pressure will result in weak flow from taps.
No backup hot water
If boiler breaks down, you have no heating or hot water.
Temperature can fluctuate
Water temperature may vary when multiple outlets are used.
System Boiler Disadvantages
Requires cylinder space
Need room for hot water cylinder, usually in airing cupboard.
Can run out of hot water
Once cylinder empties, need to wait for it to reheat.
Heat loss from cylinder
Stored hot water loses heat over time, slightly less efficient.
More complex installation
Costs more to install than combi boiler due to additional components.
Initial recovery time
Takes time to initially heat up full cylinder after installation.
Space Requirements Comparison
Combination Boiler
Boiler unit
Required700mm H x 400mm W x 300mm D
System Boiler
Boiler unit
Required700mm H x 400mm W x 300mm D
Hot water cylinder
Required1500mm H x 450mm diameter
Annual Running Costs Comparison
| Property Size | Combination Boiler | System Boiler | Difference |
|---|---|---|---|
| Small (1-2 bed) | £950 | £1030 | £80(Combination Boiler cheaper) |
| Medium (3-4 bed) | £1375 | £1505 | £130(Combination Boiler cheaper) |
| Large (4+ bed) | £1800 | £1980 | £180(Combination Boiler cheaper) |
Which Should You Choose?
Choose Combination Boiler If...
✓ Best suited for:
Small to medium homes (1-3 bedrooms) with 1-2 bathrooms, flats, properties with limited space, homes with good mains water pressure
✗ Not suitable for:
Large homes with multiple bathrooms being used simultaneously, properties with poor mains water pressure, homes with very high hot water demand
Choose System Boiler If...
✓ Best suited for:
Medium to large homes (3-5 bedrooms) with 2+ bathrooms, properties with multiple family members, homes requiring simultaneous hot water to several outlets, properties suitable for solar thermal panels
✗ Not suitable for:
Small flats or homes with limited space for a cylinder, properties with single bathroom and low hot water usage, homes where space is at an absolute premium
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