Combi Boiler Size Guide

Looking for a new combi boiler but unsure what size to opt for? Any size of combi boiler will provide heating and instant hot water, but the size of the boiler you choose can depend on a number of different factors, from the number of radiators in your home to the amount of bathrooms. 

Ideal Heating shares advice on which combi boiler size will be the best fit for your home.  

What Does Combi Boiler Size Mean?

The size of a combi boiler is actually related to its output in kilowatts (kW) rather than the physical height, depth or width. The more power the combi boiler can generate in kWs, the bigger it is in terms of ‘size’. 

For example, our combi models are available from 24 to 40kW. The size or power difference is due to the way these models operate; combi boilers generally have larger outputs in order to heat water as it’s required. Read here to find out everything you need to know about how a combi boiler works. 

What Does kW Output Mean For A Combi Boiler?

A kilowatt (kW) is equal to 1,000 watts and, in any situation, is a unit that helps measure power generated per second. For example, when looking at a 35kW boiler, the ‘35’ figure demonstrates the maximum power the boiler is capable of producing each second.

When we’re thinking about combi boilers, we can break it down quite simply: a 35kW boiler uses 35,000 watts (35 kW) of power per second to heat the water we need to keep our homes warm.

The higher the kW figure, the more powerful your boiler will be. However, that doesn’t mean you should always choose the highest kW boiler out there - it’s most important to choose a boiler size that will suit your individual circumstance to avoid wasting energy unnecessarily.

What Size Combi Boiler Do I Need For My Home?

Choosing the right combi boiler for your property depends on several factors. The main things you need to consider when calculating the optimal output are the size of your home, the number of radiators and how many baths and showers it has.

To help out, we’ve created a quick and easy tool to help you find your new boiler. Our boiler selector will suggest combi boiler models that are the perfect fit for your needs.

It’s important to note that if you’re looking to replace your combi boiler as part of a wider renovation project, you shouldn’t pick a model that’s the same size as your current one. For example, adding a conservatory or en-suite bathroom will mean you need a larger boiler for the increased space, radiators or number of taps and showers.     

Combi boilers typically need more power than system or heat only boilers because they heat up the hot water instantly. Read more about the advantages of combi boilers here.

How Many Radiators Can A 24kW Combi Boiler Run?

A 24kW combi boiler can heat up to 10 radiators, making it great for a smaller sized home. 

How Many Radiators Can A 28kW Combi Boiler Run?

A 28 kW combi boiler can heat about 10-15 radiators, making it the perfect option for a medium sized home. 

How Many Radiators Can A 32kW Combi Boiler Run?

For a larger home with 15-20 radiators, a 32kW combi boiler is a great option.

What Size Combi Boiler (in kW) Should I Choose For A One Bedroom Flat?

A 24 - 27kW combi boiler, such as Ideal Heating’s compact Vogue Max Comb 26kWi, would be suitable for a small one bedroom house or flat

If the property features one bedroom and a shower but no bath, and less than 10 radiators, there isn’t a huge amount of space to heat up and there isn’t going to be a lot of competition for using the hot water. An efficient combi boiler will provide all the heating and hot water this property needs — and it won’t take up too much precious space either. 

What Size Combi Boiler Do I Need For A 3 Bedroom House?

For a three bedroom home you should look for a 28-34 kW combi boiler, such as Ideal Heating’s Vogue Max Combi 32kW. 

For a home containing three bedrooms, a bath and a shower, and around 10-15 radiators, a higher kW combi boiler will be needed. With more rooms and a family occupying the property, there’s plenty of space to heat and increased demand for hot water. 

What Size Combi Boiler Do I Need For A 5 Bedroom House?

For larger family homes, a heat system boiler may be a better fit than a combi boiler as you may find the increased demand for hot water can only be met by installing a separate hot water tank. To find out more take a look at the difference between combi, heat and system boilers here.

What Happens If My Combi Boiler Is the Wrong Size?

If you select a combi boiler that’s the wrong size it can cause potential issues in your home. For example - a combi boiler that is too big could increase the cost and efficiency of your boiler, whereas if you select a combi boiler that is too small, you may end up with too little power to heat your home.

It’s important to select the right size boiler for your property, to ensure it can efficiently provide the heat and hot water you need.

What Is The Physical Size Of A Combi Boiler?

As a combi boiler has no need for a separate cylinder or water tank it will be very compact in size. This means that a combi boiler can be the ideal solution for smaller sized homes that do not have as much space.