Heat only boiler sizing guide

Choosing the right heat only boiler for your home is crucial for efficient heating and energy cost savings. Whether you have a small apartment or a large house with multiple bathrooms, various factors must be considered when determining the size of your heat only boiler.

This guide will help you understand the different boiler sizes available and how to select the ideal one based on your home's heating demands. From the recommended kW outputs for various home sizes to the importance of balancing efficiency with power, learn everything you need to know to make an informed decision.

If you are looking for more information, our handy blog on the advantages of heat only boilers is here to help.

What is a Heat Only boiler?

Heat only boilers are a common feature in many older UK homes, especially those constructed before the 1970s. If your heating setup includes a hot water cylinder and two water tanks (usually located in the loft), it’s likely you have a heat only boiler. These components collaborate to supply hot water to your radiators, taps, and showers.

For a deeper understanding, check out our blog post, 'What is a Heat only boiler,' for more insights.

Still unsure which boiler you need? Read our blog on differences between a Combi, System and Heat only boilers.

What is boiler sizing? 

Boiler sizing isn’t about the physical space your unit takes up. It actually refers to the amount of heat energy your boiler can generate, measured in kilowatts (kW). At Ideal, our sizes for heat only boilers range from 12kW to over 30kW, allowing us to provide heating solutions for all kinds of homes. 

What factors affect Heat Only boiler sizing?

Once you have selected the boiler type for your home, you will need to choose the correct boiler size for your home’s heating requirements. A few factors to take into account include:

• The number of radiators

• Number of bedrooms

• How well insulated the home is

Why does Heat Only boiler sizing matter?

An incorrectly sized boiler can lead to overheating, underheating, lack of efficiency, and money wasted over time. 

A boiler that is too large will overheat your home and dump too much heat into the system too fast, resulting in short-cycling (switching on and off) and fuel waste, which in turn wastes your money. Meanwhile, a boiler that is too small won’t be able to sufficiently heat your home, leaving you cold in the winter months. 

Heat Only boiler size calculator chart

Heat only boilers store water ahead of time, meaning they are built with a smaller power unit than Combi boilers. Below we have shared the ideal boiler size depending on your home’s heating requirements.

Please note these are general guidelines for what size boiler you should have. We always recommend consulting a trained Ideal Heating engineer before making a final decision. For example, a smaller home that is less insulated may need a larger boiler. Likewise, a small home with a high number of occupants might need a larger quantity of hot water needed, making a larger boiler necessary.  

Size of Ideal Heating Heat Only boilers

See the different sizes of heat only boilers we offer.

Discover more top tips on the Ideal Heating blog, or for further advice on choosing the best heating system, use our boiler selector tool. Also, if you encounter any issues with your Heat only boiler, head to our troubleshooting guide.