How to Calculate BTU?

Everyone wants to stay warm at home, but when it comes to knowing how much heat output is required in a specific room to produce the right temperature, it can prove to be confusing.

However, by using something called the British Thermal Unit (BTU) you can ensure the heating system you use is up to the job. Let us explain how it works in more detail below.

What is BTU?

BTU is the measurement used to calculate how much heat output is required to keep a room warm. While this may sound like you need a physics or maths degree to find the answer, it is not as difficult as it sounds.

A single BTU is equivalent to 1055 joules (a unit of energy in the International System of Units). This is required to heat 0.45kg (1lb) of water by -17°C (1°F).

This means the higher the BTU value, the more heat is produced. For example, the Tate anthracite grey double vertical radiator has a high BTU output of 5618. This is why it is usually purchased and installed in larger rooms due to its ability to provide adequate warmth. At the other end of the scale, something like the Winchester heated towel rail 700 x 400 has a BTU output of 431. This will not enable it to heat an entire room, no matter its size, and is only suitable for drying towels.

It is important to find the right BTU for the room as if it is too low, the temperature will not be sufficient. If the BTU is too high, the energy being produced will not be used efficiently and lead to higher energy bills.

How do I work out the correct BTU for the room?

If you want to do the calculations manually you can jump below, however if you just want to use our calculator then there are two options depending if you have single or double glazing windows and door.s 

Double Glazing

Double Glazing

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Vertical
Horizontal

Double Glazing

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Single Glazing

Two columns
Vertical
Horizontal

Single Glazing

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There are four main steps to follow in order to work out the correct BTU for any room:

  1. Think about the type of room you want to heat. Different rooms will have different requirements, such as bathrooms, bedrooms, living rooms and kitchens etc.

Although requirements will differ from household to household at various times of the year, you can use the below as a general guideline:

  • Bedroom/Hallway/Cloakroom: 18°C/65°F
  • Living Room/Dining Room: 21-22°C/70-72°F
  • Kitchen: 20°C/68°F
  • Bathroom: 21°C/70°F
  1. Once you have determined the heating requirements for the room, you will need to measure it. Use a tape measure to take note of the room’s height, width and length. If the room is odd-shaped, divide the room into rectangles before measuring each section separately and adding the calculations of the room together to get the full dimensions.
  2. Heat loss occurs in every area of the home, so this also has to be taken into account. Take note of any windows or doors in the room and whether they are single or double glazed – even with up-to-date insulation sealing more heat is lost through single glazing than double glazing.

4. Now you have all of this information, you can calculate the BTU using the table below:

BTU Examples

To give you more insight on how much BTU is required to heat certain rooms in the house, we have put together a few examples to help.

These calculations are only intended to work as a rough guide. In order to accurately calculate the BTU for any room in your home we always recommend you hire a qualified and experienced professional plumber.

Living room with double glazed window

Dimensions: 4.8m (length) x 4.8 (width) x 2.4m (height) = 55.3 x 135 (taking into account the double glazed window) = 7465 (BTU).

The room would require two radiators each with an output of at least 3733 BTU. The Tate Anthracite Grey Double Horizontal Radiator (600 x 1000) would offer the ideal solution.

Family bathroom with double glazed window

Dimensions: 2.72m (length) x 2.39m (width) x 2.4m (height) = 15.6 x 121.5 (taking into account the double glazed window) = 1896 (BTU)

This would translate into either a single radiator or heated towel unit that can produce at least 1896 BTU. A great example of this would be our White Heated Town Rail (1200 x 600).

Double bedroom with double glazed window

Dimensions: 4.0m (length) x 4.5m (width) x 2.4 (height) = 43.2 x 108 (taking into account the double glazed window) = 4666 BTU.

A single radiator with a BTU output of at least 4666 BTU would work in this room. The Dulwich Vertical White Triple Column Radiator is the ideal solution in this case.

Have you calculated your BTU?

With the BTU now calculated for the room, you can focus on choosing the right system to suit the space. Take a look at our fantastic range of designer radiators and heated towel rails and we guarantee you’ll find something that will keep you warm and add something special to the room.