Boiler size calculator – What size kilowatt (kW) boiler do I need for my home?

what size boiler

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If you buy ANY Viessmann boiler from Boiler Central, you get a 12-year warranty. Free parts, labour & call outs!

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Boiler sizing calculator (Viessmann)

To say that boilers are available in different shapes and sizes and offer higher or lower litres per minute would not be accurate enough.

They are almost always rectangular.

However, they are available in a range of outputs and knowing what size boiler you need for your home is extremely important. These factors will affect the new boiler cost.

How to pick the right size boiler for your home

Lets look at what factors do you need to consider to find the right boiler before deciding on a boiler size or boiler heat that your home needs?

Here’s what you need to know to answer the question – What kilowatt boiler do I need?

The questions below will work as your boiler size calculator:

  • The number of bathrooms
  • The number of radiators
  • The number of people in the home- the demand for hot water

Please note that the above information gives you a pretty good idea of which boiler size and hot water cylinder you will need.

By the way, people often refer to the “size of the boiler”. What this really means is its higher output, which is measured in kilowatts, or kW.

What is a Kilowatt? A Kilowatt or kW is a unit that is used to measure boiler outputs or flow rates. In simple terms; how much water can be used at once.

Use our online quote tool to know the boiler size that your home needs.

You’ll see fixed prices for boiler replacements that are the perfect match for your home’s power needs.

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Boiler size calculator

What size boiler do i need for 4 bed home

Choosing a suitable size boiler is extremely crucial for two main reasons:

  1. Does not meet the heating and hot water requirements of your home if you undercut it.
  2. Opting for a larger kW than you need will be a waste of money.

To work out what size boiler you need for your home, use our boiler calculator here: Boiler Calculator

How big a Boiler do I Need?

An under-sized boiler has difficulty in meeting your home’s central heating needs, resulting in a not powerful enough heating system for your radiators, hot water for your baths/ showers or daily needs.

Opting for the larger size boiler for your house than needed will cost more money than is necessary.

Choosing the right size/ kW type of boiler will ensure that your home is warm enough and you always have enough hot water when you need it.

2 – Burning extra gas can easily waste a large amount of money

boiler size calculator

An overloaded offers no additional benefits.

Although modern boilers adapt to lower requirements.

By not using the boiler calculator and guessing what size boiler you need and going larger will mean you have spent considerably more money on a boiler model that you do not need.

If the boiler you choose is not upscale, you may be wasting a lot of money on burning unnecessary gas.

Please Note: If you are planning an extension of your home that would include additional showers, It may be worth considering a boiler with higher power (kW) and a larger hot water tank.

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Combi boiler sizes for your home, based on kilowatt ratings what size boiler

The size of the combi boiler for your home depends on the amount of bathrooms. Check the table below.

The boiler sizing calculator suggests if you have more than 1 bathroom in your home, you need a boiler with more power to handle the higher hot water demand, especially when people tend to shower at the same time.

What size combi boiler do i need? The more bathrooms you need heated, the larger the boiler you will need.

The combi boiler size calculator is listed below:

No. of Bathrooms
or Showers
Boiler Size
(minimum) 
Recommended
Boiler
 
126kWViessmann Vitodens 050-W 29kWGet Quotes
230kWViessmann Vitodens 100-W 30kWGet Quotes
335kWViessmann Vitodens 050-W 35kWGet Quotes
3+35kW*Viessmann Vitodens 111-W 35kWGet Quotes

Boiler size based on the number of bedrooms in your home

You should calculate the size of the boiler based on the number of bathrooms / showers (as shown above).

What size KW boiler do I need for my home?

The following is a rough guideline for the asked questions:

What size boiler do i need for a 2 bed home?

What size boiler do i need for a 3 bed home?

What size boiler do i need for a 4 bed home?

What size boiler do i need for a 5 plus larger home?

 Minimum kW Size 
What size boiler for…1 Bath/Shower 2 Baths/Showers 
2 Bedroom House26kW29kWGet Quotes
3 Bedroom House29kW35kWGet Quotes
4 Bedroom House29kW35kWGet Quotes
5 Bedroom House35kW35kWGet Quotes

Boiler sizes for large homes with multiple bathrooms

Viessmann has managed to lead us into the future and to build a hybrid boiler – the Viessmann 111-W. veissmann boilers

What size KW boiler do I need for my home?

They merged the DNA of a traditional boiler and a modern boiler to create their own.

It is a combi boiler that stores the water within the unit enabling it to suit homes with up to 5 bathrooms.

At Boiler Central we offer Viessmann boilers with a massive 12-year warranty.

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How to calculate what size system or regular boiler you need

Regular boilers are also called heat only boilers, featuring a boiler, hot water tank and a cold water tank. The hot water tank is usually found in an airing cupboard and the cold water tank resides in the loft in most cases.

The number of radiators are the main factor with regular boilers as well as the number of bathrooms that you have. Both of these give us an idea of the heat only boiler size that you will require.

If you are asking yourself what size boiler do you need for a certain amount of radiators, see the table below which gives you an idea of regular boilers for different radiator configurations.

What size boiler for…Boiler Size CalculationMinimum kW SizeRecommended Model
6 Radiators6x 1.5kW + 3kW12kWIdeal Logic 12kW
8 Radiators8x 1.5kW + 3kW15kWViessmann Vitodens 100-W 16kW
12 Radiators12x 1.5kW + 3kW21kWIdeal Logic 24kW
15 Radiators15x 1.5kW + 3kW26kWViessmann Vitodens 100-W 26kW
20 Radiators20x 1.5kW + 3kW33kWViessmann Vitodens 100-W 35kW

Converting from a conventional to a combi boiler

Believe it or not, best combi boilers are great, cost-effective to operate and deliver instant hot water without delay from your shower, bath or faucet.

No wonder the conversion to a combi boiler is the most common New Year’s resolution in the UK.

What size KW boiler do I need for my home?

Although converting can be a pretty expensive job, our Boiler Central will offer you prices for boiler upgrades that are pocket friendly.

See the table below to see what size boiler you need for the following amount of baths/showers:

Number of
Baths/Showers
Boiler Size
(Minimum)
Recommended
Model
 
126kWViessmann Vitodens 050-W 29kWGet Quotes
230kWViessmann Vitodens 100-W 30kWGet Quotes
335kWViessmann Vitodens 050-W 35kWGet Quotes
3+*35kW*Viessmann Vitodens 111-W 35kWGet Quotes

It is worth noting that the size of the combi boiler that you would need if you are changing from a regular boiler is no different than if you already had a combi boiler.

All you need to do is to consider your hot water demand as indicated above.

If you want to buy a new boiler replacement, but have no idea what size you need, the click the buttons below to get a fixed price online.

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FAQ’s on boiler sizes for your home

What is the best boiler for a small house?

The best boiler for a small house depends on what is perceived as ‘small’. You would generally say that a home with 1-2 bedrooms is classed a small house. This includes flats and apartments too.

Therefore based on a 1-2 bedroom small house, the best boiler we would recommend would be the Viessmann Vitodens 050-W 29kW combi boiler.

What size boiler do I need for a 3 bedroom house?

The best size boiler for a 3 bedroom house is again the Viessmann Vitodens 050-W combi boiler.

This is probably joint with the Worcester Bosch Greenstar 2000 which is the new boiler from Worcester in 2021.

Any kW rating from 25kW to 35Kw would be fine, however somewhere around 29-30kW would be most suited to a home of 3 bedrooms.

Get a fixed online quote on those two boilers in 20 seconds – click here

What size boiler do i need for a 4 bedroom house?

The best size boiler for a 4 bedroom house is the Worcester Bosch 8000 Style combi boiler OR system boiler, depending on your home type.

For another option, the Viessmann Vitodens 100-W combi or system boiler would be a great fit for a home with 4 bedrooms.

Either of the above in a 35kW rating would be perfect for a 4 bedroom home.

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What size boiler do I need for a 5 bedroom house?

The best size boiler for a 5 bedroom house would be the Worcester Bosch 8000 Style in 35kW or 40kW size.

Usually in a house with 5 bedrooms there is a system boiler that heats the home. It would be best to keep the system boiler in a 5 bedroom house as there will always be hot water ready sorted in the tank.

A combi boiler of 40kW would probably be ok, but a system boiler would be much more practical and you would have no issues with hot water demand.

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What happens if my boiler is too small?

If your boiler is too small ofr your home then you may find that you are requiring hot water but it is not running as hot as it can, or should be.

This will be down to having a boiler that is too small for the size house. You would be best to complete our online survey and see the boilers that we offer that would be perfect for your size home.

If you have moved into a property and think your boiler is too small, you should get a quote on a new boiler in 20 seconds – click here

How many radiators will my boiler size run?

Many of our customers ask us how many radiators their boiler size will run. This is dependent on a few factors but generally speaking, the larger your home, the more radiators that you will have.

This means that it’s easier to categorise your boiler size requirements into how many bedrooms your home has, as the FAQ’s above show.

Although the above is not always the technical answer, below you can see how we work out what size boiler you can have for the amount of radiators:

What size boiler for…Boiler Size CalculationMinimum kW SizeRecommended Model
6 Radiators6x 1.5kW + 3kW12kWIdeal Logic 12kW
8 Radiators8x 1.5kW + 3kW15kWViessmann Vitodens 100-W 16kW
12 Radiators12x 1.5kW + 3kW21kWIdeal Logic 24kW
15 Radiators15x 1.5kW + 3kW26kWViessmann Vitodens 100-W 26kW
20 Radiators20x 1.5kW + 3kW33kWViessmann Vitodens 100-W 35kW

How many radiators will a 30kW boiler run?

A 30kW boiler will typically run 15 radiators with ease. The boilers that we recommend for this range would be the Viessmann Vitodens 050-W combi boiler. Get an online quote on this boiler by clicking here.

How many radiators can a 24kW boiler run?

A 24kW boiler will run around 12 radiators in a typical home. The Vokera EasiHeat 25kW combi boiler would be an ideal choice. Get an online quote on this boiler by clicking here.

How many radiators can a 35kW boiler run?

A 35kW boiler will run 20-25 radiators with no problems at all. The Worcester Bosch 8000 Style boiler would be a perfect fit for this range.

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How to get the Best Price on the Right Size New Boiler?

Without bragging, Purchase from us! what size boiler for my home

We are a nationwide online boiler installation company with over 5 stars that comes from a dandy load of satisfied customers.

We are an online business hence our operating costs are low, which means that we transfer these savings to our customers to make sure they always get the best deal for a new boiler whether it is a conventional boiler, system boiler or the best combi boiler.

Due to the volumes we have installed, we can also access the exclusive warranty of our partner manufacturers.

What size KW boiler do I need for my home?

For example, we can offer a massive 15 years of protection for the Viessmann 050-W Series, while your normal installer will give you 7 years. 

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