What Size Boiler Do I Need? How To Choose The Best Boiler For Your Needs

Oct-2020 / 4 min read

Reading Time: 4 minutes

Boilers are arguably one of the most essential appliances that can be found in every household. After all, they provide us with hot water and hot air to stay warm and clean. However, when you need to replace an old boiler or purchase a new one, not many realise how important it is to find the perfect boiler in terms of size.

Any miscalculation on the size may lead to stress and more unnecessary expenses in the future. And this guide can help you prevent this from happening. Moreover, if you’re asking, “what size boiler do I need?” we can help you out! Below, we have a list of items you should consider while determining what size boiler you need exactly. We will be including a sample boiler size guide, as well as links to some boiler manufacturers’ boiler sizing calculator.

Why Do I Need To Find The Right Size?

A miscalculation on what boiler size you need can be costly. A boiler that is too small, for example, will have trouble providing enough heat for your central heating system, nor will it have enough hot water for your shower.

Alternatively, a boiler too large in size will result in a lot of wasted energy. Your boiler will be producing a lot more heat than what is needed, thus using more electricity or burning more gas. And as you already know,  

More electricity or gas used = More expensive electricity/gas bills.

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What Size Boiler Do I Need: How Boiler Size Is Measured

Before we go on, it is important for us to be on the same page. When we say “boiler size,” we are not talking about the physical size of the boiler, but rather the boiler’s output in kilowatts (kW) or the amount of energy the boiler puts out in the form of heat. Typically, the more heat and hot water you need, the higher the energy output you will require. However, many other things play a part in determining what size boiler is best for your home.

Factors To Consider When Deciding What Size Boiler You Need For Your Home

Here are some of the things that you should take into consideration while choosing an appropriately sized boiler for your home:

How Big Is Your Property?

The size of your property is one of the most important things to consider when you’re trying to determine what boiler size you need. To put it simply, the larger your property is, the more space you will have to fill with heat and more bathrooms and sinks you will have to fill with hot water. Hence, under “how big is your property?” you will also have to ask:

How Many Radiators Do You Have?

An average apartment or a small house will have roughly around ten radiators. That means you will have to get a boiler that can power up to ten radiators all at the same time.

Do You Have Multiple Bathrooms?

Moreover, you will also want to find out how many bathrooms your new boiler will have to supply hot water. Some boilers are not able to accommodate supplying hot water to more than one location at a time, so that is also something you will have to take note of. It would also be smart to determine if you will want hot water to be supplied to other areas in your home, like the kitchen, guest comfort room, and laundry area.

How Many People Live In Your Home?

Aside from how many rooms and radiators you will be supplying heating and hot water to, you also have to determine the demand for heating and hot water in your home.

For example, if there are only two bathrooms in your house, but four people are using each, you will have to take the fact that there are eight people in need of hot water, rather than focusing on the fact that there are only two bathrooms in your home.

What Type Of Boiler Do You Plan On Purchasing?

Before you ask yourself, “what size boiler do I need?” you should also determine what kind of boiler you plan on purchasing. Do you want a combi boiler, a standard boiler, or a system boiler? While it doesn’t seem like it, the type of boiler you purchase does play a part in determining what size boiler you need.

That is because combi boilers usually heat up water instantaneously, requiring more energy than other types of boilers. Standard boilers and system boilers, on the other hand, make use of a hot water cylinder or tank, thus storing hot water for longer periods of time. Moreover, the only difference between the two is that a standard boiler gets water from a cold water tank, while a system boiler gets water directly from the pains.

These, in turn, will affect the amount of energy (kW) consumed by each type of boiler.

To read more about the different types of boilers, click here.

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Other Factors To Keep In Mind

Aside from the factors mentioned above, here are a few things you will want to remember while determining the right size of boiler for your home.

  • Account for heat loss in your home. Aside from the demand for heating and hot water and the size of the property, the insulation and size and number of windows you have will also come into play.
  • Every type of fuel has a different rate of efficiency. That means if you are using a type of fuel that is less efficient than others, you may need to use a larger boiler size.
  • The water pressure in your home will definitely determine what size of boiler you need. This is especially important if you are using a combi boiler, as combi boilers should be big enough to accommodate the amount of water passing through it. That means the higher the flow rate, the bigger boiler you will need.

Most Common Size of Boilers

Here are the most common types of boilers out in the market:

Standard Boilers

  • 9-18 kW (below ten radiators)
  • 18-26 kW (10-15 radiators)
  • 27-40 kW (15-20 radiators)

Combi Boilers

  • 24-27 kW (below ten radiators)
  • 28-34 kW (10-15 radiators)
  • 35-42 kW (15-20 radiators)

System Boilers

  • 9-18 kW (below ten radiators)
  • 18-26 kW (10-15 radiators)
  • 27-40 kW (15-20 radiators)

Boiler Size Calculator Links

To calculate boiler size more accurately, you may use the boiler size calculator specially made by these boiler manufacturers:

If you’d rather have a professional do a survey of what boiler size you need for your home, you may always contact a local gas safe engineer in your area. Better yet, book an appointment with Plumbingforce today! We can come to your property in no time!

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