What Size Boiler Do I Need?
What Size Boiler Do I Need?

Most of us have only a bare understanding of how our central heating system works and there's nothing wrong with that. We can't all be gas engineers.

Unfortunately, when something goes wrong with your boiler, this means you don't really know what to do. Sometimes you call in a technician who turns a few knobs and fixes the problem. Sometimes, a boiler just can't be repaired anymore.

Your average UK boiler has a product shelf life of between 10 and 15 years. If you are a homeowner, this means you are going to have to go through the boiler replacement process more than once. Familiarisation now could save you a world of blood, sweat and tears in future.

The Three Main Types of UK Boiler

There are three main types of boilers in regular use today. The combi, the system, and the regular boiler .

In the UK, most of us have what we call a combi boiler. A combi boiler operates by producing hot water as it is needed, bypassing the need for a hot water tank. This is effective because it saves space and gives you one appliance to worry about, rather than two.

A system boiler is often used in larger buildings which need a steady supply of hot water. They have a separate cylinder where they can store hot water, whereas the combi boiler produces it on demand.

A regular boiler produces hot water which it stores in a hot water tank until it is needed. If you use all the hot water, you will need to wait for the boiler to produce more. Think of the boilers in the 80s and 90s.

How to tell which size of boiler you need?

Boiler output is measured in Kilowatts and if that output is too low, you will fail to heat your home effectively. If it is too high, you will burn through more energy than you need to use.

As a rough guide, use the following boiler sizes for your home, assuming you purchase a combi boiler:

• For a home with 1 bathroom/shower the minimum boiler size should be 26 KW
• For a home with 2 bathrooms/showers the minimum boiler size is 30 KW
• If your home has three showers, your boiler must have an output greater than 35 KW
• And if you have more than three, you should consider sizing up to the system or conventional boiler discussed above. It has been designed for larger properties like yours.

If you like, we can also calculate the number of radiators and use this as a guide to determine boiler size, too.

Choosing a boiler size by radiator numbers:

• 6 radiators need 12 KW+ to run
• 12 radiators need 21 KW+
• 20 radiators need 33KW+
And so on.

In a third way to measure the size of boiler needed, work by house size. Anything under two bedrooms should use 29 KW or there abouts. Anything over a two bedroom house should use a 35 KW combi boiler or larger.

Is my house too big for a combi boiler?

Finally, how big is too big for a combi? We recommend no bigger than 3 bathrooms or 5 bedrooms before you are better off with a regular boiler, instead.