When looking to purchase a new boiler you may get confused by the amount of products online, the various types of products and also the size in kilowatts (kW). So let’s start with the type of boiler you need.
What type of boiler do I have?
If you already have a boiler installed, the most common thing an installer will do is replace it with a like-for-like. However, it’s likely that your old appliance is over 10 years old and building regulations have changed. This may affect your situation.
One of the big changes that do catch most people out and ultimately invalidate a boiler warranty is the room around the boiler.
A professional GasSafe heating installer will advise, but it’s good to be in the know eh?
There are three types of domestic boilers:
- Combination Boilers
- System Boilers
- Heat-only Boilers (also known as regular boilers)
These don’t account for renewable technology such as heat pumps and biomass.
An easy method to distinguish what type of appliance you have is by understanding if you have a tank or hot water cylinder. If you don’t have one of these, then you probably have a combination boiler.
Both system and regular heat-only boilers have tanks. Regular boilers may have two; one cylinder and an expansion vessel.
What size boiler do you need?
Boiler size is defined by the size of your property, the number of radiators and also bathrooms. If you have two or three bathrooms you will want a bigger size boiler (kW). Also, bigger properties tend to use system boilers as opposed to their combi siblings. They can supply a constant level of hot water throughout a home, even when multiple showers and taps are open simultaneously.
Combination boiler size comparison
The table below is a guide and it’s always advised that you get a home survey to understand your needs correctly. You can use our boiler quote tool here to get the make and model suitable for your home.
| Bedrooms | Bathrooms | Radiators | Boiler Size |
| 1-2 | 1 | 0 - 10 | 24 - 27kW |
| 3-4 | 2-3 | 10 + | 28 - 34kW |
| 4 + | 3 + | 20 + | 35 - 43kW |
System and Heat-Only Boiler Size Comparison
The table below is a guide and it’s always advised that you get a home survey to understand your needs correctly. You can use our boiler quote tool here to get the make and model suitable for your home.
| Bedrooms | Bathrooms | Radiators | Boiler Size |
| 1-2 | 1 | 0 - 10 | 9 -18kW |
| 3-4 | 2-3 | 10 + | 18 - 26kW |
| 4 + | 3 + | 20 + | 27 - 40kW |
What if you don’t want a like-for-like boiler?
There are some instances where a like-for-like boiler exchange is not suitable. There are still homes that operate with a back boiler, these are appliances that traditionally sit behind the fireplace. They are less efficient than the new combination boilers and will not be replaced with another back boiler.
There are also cases where homes have been extended but still have a smaller powered boiler and need a larger one. Ideally, a system boiler would be more suitable but the correct size combi will also do the job.
You basically need the correct room for a combination boiler, ideally situated on a wall with external access for the flue. If you upgrade to a system boiler, you will need additional room for the tank.
