When updating your home, one of the trickiest things to consider is your heating.

Shopping for a radiator or heated towel rail is difficult enough, but knowing whether it is suitable to heat your room is another matter entirely. Luckily, help is at hand, and it comes in the form of three simple letters: BTU

What is BTU?

If you’ve only just come across the term, welcome to the club! BTU stands for British Thermal Unit, and is the standard way to work out how much heat output is required to keep your room warm.

If you remember any of your science lessons in school or actually want to know the technical detail, 1 BTU is equal to 1055 joules and is the amount of energy needed to heat 0.45kg (1lb) of water by -17°C (1°F). Make sense?

In simple terms, the higher the BTU, the greater the heat output. For example, the Salvador anthracite grey double vertical radiator has a BTU output of 5618, meaning it is suitable for heating very large rooms. Whereas the Aziz heated towel rail 700 x 400 has a BTU output of 431, meaning it really is only suitable for keeping towels warm, not for heating a whole room.

Buy heating with a BTU output that is too high for your room, and you’ll literally be burning extra cash on unnecessary energy bills. Buy one with a BTU output that is too low, and you simply won’t get enough heat, meaning you’ll have it cranked up to maximum the whole time. So it's important you know how to calculate the BTU for your room.

Video showing how to calculate BTU

How to work out the correct BTU output for your room

  1. Take into account the type of room you are looking to heat—is it a bathroom, bedroom, kitchen, dining room, living room or hallway?

Different room types, generally, require slightly different temperatures. Here are some typical examples below (but you may prefer your room to be warmer or cooler):

  • Living Room/Dining Room: 21-22°C/70-72°F
  • Bathroom: 21°C/70°F
  • Kitchen: 20°C/68°F
  • Bedroom/Hallway/Cloakroom: 18°C/65°F
  1. Measure the length, width and height in metres and note this down. (If you have an odd-shaped layout, divide the room into separate rectangles and measure each one separately)

  2. Next, you have to take into account heat loss:

  • Do you have any windows or doors?
  • Are they single or double glazed?
  1. You are now ready to perform your BTU calculation, using the tables below:

BTU calculation table - double glazing

BTU calculation table - single glazing

BTU guides

Here are some general room sizes and the BTU required to heat them to a certain temperature:

Family bathroom with double glazed window

2.72m L x 2.39m W x 2.4m H = 15.6 x 121.5 (allowance for double glazed windows) = 1896 BTU

You will require 1 x radiator or heated towel radiator with an output of at least 1896 BTU. Something like the White heated towel rail 1200 x 600 would be ideal.

The Heating Co. White heated towel rail 1200 x 600

Living room with double glazed window

4.8m L x 4.8m W x 2.4m H = 55.3 x 135 (allowance for double glazed windows) = 7465 BTU

You will require 2 x radiators with a BTU output of at least 3733 BTU. Something like the Salvador anthracite grey double horizontal radiator 600 x 1000 would be ideal.

The Heating Co. Salvador anthracite grey double horizontal radiator

Double bedroom with double glazed window

4.0m L x 4.5m W x 2.4m H = 43.2 x 108 (allowance for double glazed windows) = 4666 BTU

You will require 1 x radiator with a BTU output of at least 4666 BTU. Something like the Santa Fe vertical white triple column radiator (pictured below) would be ideal.

The Heating Co. Santa Fe vertical white triple column radiator

Of course, the above calculations are meant as a rough guide to choosing your heating. We would thoroughly recommend hiring a qualified and experienced plumber to fully calculate your required BTU. They will take other factors into account, including the number of external walls and the size of windows and doors.

Calculated your BTU?

Now you've calculated your required BTU output, you can get on with the all-important job of selecting your new heating. Take a browse through our wide range of designer radiators and heated towel rails and find something that will make your interiors look and feel hot, hot, hot!

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