How Big Does My Boiler Need To Be?

Boilers don't last forever, and when it comes time to replace yours, there are a few questions that come up. The question that's the most important is by far "What size boiler do I need for my home?" or "How many kW's does my boiler need to have?". The answer to your questions depends on a few things, which we will go into below

Making sure you have the correct boiler fitted with save you money in the long term and also ensure you have all the heat and hot water you need.

With modern combi boilers lasting upwards of 15 years, it's important to get it right.

How are boiler sizes measured?

All boilers are measured by their energy output in the form of heat, known as a kilowatt (kW). In simple terms, the more heat and hot water you need, and the larger your home, the higher you will want the kW rating of your boiler to be.

Should I Oversize My Boiler

In days gone by the general consensus and advice from heating engineers was to buy a boiler that had a higher kW rating than needed on paper to compensate through heat loss, as homes weren't as thermally efficient. With advancements in how we insulate our homes and the technology used in insulation, homes retain heat better now so this is no longer needed as you would simply be wasting energy and money.

Sizing Up For Hot Water

The flow of hot water that a combi boiler can produce is measured in litres per minute or LPM, this tells you how fast a combi boiler can heat hot water. This rating can vary from as little as 9 LPM up to 25 LPM for large boilers.

The majority of UK households have a combi boiler fitted as they provide heating and hot water at the same time without the need for a hot water storage tank. However, if you need to run more than one shower or bath at the same time you may consider a conventional system boiler. These systems have a separate hot water tank that stores hot water rather than heating it when it's required.

The higher the flow rate you require, for power showers or filling baths quicker, the higher output (LPM) combi-boiler you will need. Conventional boilers are more useful for larger homes but require space for storing a separate hot water tank and are more expensive to install.

How many radiators?

The number of radiators that you require will be the deciding factor when choosing what kW your boiler needs to be, this is to ensure that all of them are heated correctly and your home is the right temperature.

A small flat or apartment with only a few rooms and radiators will require a low kW boiler, usually 12-24 kW. An average 3-4 bed house with around 10 radiators will need something a bit more powerful, usually 12-24kW. If you have a large house, with as many as 20 radiators, a large combi boiler with a rating of up to 42kW may be what you need to heat your home. At this size, you more than likely have a conventional or system boiler in place though.

Insulation

How well your home is insulated will also have an impact on the boiler that you need. If you have poor loft/cavity insulation and single-glazed windows then you would need a more powerful boiler to make up for the heat loss caused by this.

Newer built homes will be more efficient in terms of heat retention and insulation and therefore require less power to heat the home.

 Browse a selection of some of our radiators below: