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What Size Boiler Do I Need?

When you are choosing the boiler for your home, you need to consider its size, otherwise known as output. Having the right size boiler for your property is crucial to a comfortable and warm home. While your best course of action is to ask a certified heating engineer, it is still useful to have a general idea of the appropriate boiler output for you. Find the answer to the question “what size boiler do I need?” here!

Why does the boiler size matter?

Installing the right boiler for your system is key. If you get a boiler with the correct output, then you’ll enjoy a warm home without any extra running costs. There are many factors that determine the right size, which we’ll talk about in a later section.

If you have a boiler that is too small, then it won’t be able to produce enough hot water and space heating for your property. This means there’ll be cold rooms and you could run out of hot water often.

What size boiler do I need?

On the other hand, if your boiler is too big for your home, then you’ll just be wasting energy. This is because the boiler will produce more heat than you need. A boiler with an output that is larger than what is recommended will drive up your energy bills and release unnecessary emissions.

It’s important to note that a boiler’s output does not necessarily correspond to its actual size. For instance, a boiler with a higher output of 35kW does not mean that the unit will be larger than that with a 27kW unit. However, the unit dimensions might increase for particularly powerful boilers. In any case, make sure that the boiler you choose will fit in your kitchen, loft, or airing cupboard.

Determining the right boiler size for you

So how exactly can you calculate the right boiler size for you? The simplest and most reliable way is to consult your heating company, engineer, or plumber. With their in-depth knowledge of central heating systems, they will usually conduct an in-person survey of your home to accurately calculate the boiler output that you need. We recommend getting in touch with at least 3 companies. Our form helps you reach out to multiple heating companies at once, saving you valuable time.

What size boiler do I need?

The things that affect your appropriate boiler output

When trying to find the right boiler size for you, there are a few things that you need to consider.

Current boiler size

If you already have a boiler installed, then use your current boiler size as a point of reference. This doesn’t mean you should still choose a boiler with the same output, however. There could have been many changes since the boiler was installed.

For example, your home’s energy efficiency could have improved, you added an expansion or extra room, or you welcomed a new family member. All of these will now affect your choice for your new boiler.

The size of your home

How many rooms are in your home also plays a big role in determining the right boiler output for you. As a general rule, the more rooms you need heated, the larger the boiler you will need. Take a look at the following chart for rough calculations:

What size boiler do I need?

Size Of Home
Number Of Bedrooms
Number Of Bathrooms
Number Of Radiators
Boiler Output
Apartment / small house
1 - 2
24 - 27kW
Medium house
3 - 4
1- 2
28 - 34kW
Large house
35 - 42kW

This is just a general guide so the actual boiler size you need will vary depending on your specific situation. However, this chart will give you a rough idea of the boiler output that could serve your home well.

What size boiler do I need?

The number of bathrooms in your home

How many bathrooms do you have? The number will not only affect the boiler size, but also the recommended boiler type for your home. Usually, the more bathrooms in a home, the higher the hot water demand, thus a larger boiler size is needed.

Additionally, if you have 2 or more bathrooms, a conventional or system boiler is a better choice than a combi boiler. This is because combi boilers can only provide a single water flow—the water pressure diminishes as the flow is split between multiple bathrooms. So if you’re wondering “what size combi boiler do I need?” it might not actually be the right choice for you.

Your family’s heating demand

The amount of water that your household uses daily is a major factor in your choice of boiler size. You need to have enough hot water for everyone in your family. Since everyone’s hot water demands differ, you need to choose a boiler with the appropriate output that will satisfy your needs.

Usually, the more occupants in your home, the higher boiler output is needed. As such, you’ll need a big enough boiler. This is to ensure that there is enough hot water for everyone’s showers, the washing up, as well as other activities that use hot water.

What size boiler do I need? How to determine the right boiler output for you.

Ready to find the right boiler size for you?

Then you need to get in touch with professional heating engineers to calculate the boiler output you need. The more calculations you obtain, the more accurate your data will be, which is absolutely crucial when you are making such an important buying decision. Reach out to multiple heating companies by completing our free, non-binding form. You can ask for several boiler size calculations at once, saving you time and money!