W. Tombling Ltd.
What size heater do I need?
Every day we are asked ‘what size heater do I need’ or ‘what size heater do I need for a building of x square feet or meters’ no matter how the question is worded the answer is the same – you need to do a heatloss calculation!
What is heatloss?
All buildings loose heat through their walls, roof, floor, doors and windows, and through ventilation and air leaks in the skin of the building, the total of all these losses is called the heatloss.
Why is heatloss so important?
To raise the temperature of a building you must replace
Put anther way, to raise the temperature of a building the output of the heaters installed must exceed it's heatloss.
This is a very important concept:-
This disproves a very common misconception; ‘a small heater is better than none’. The only way to effectively heat a building is to install heater(s) with a total output greater than the heatloss.
But I’m not a heating engineer how do I work out the heatloss?
We have produced a step by step guide how to perform a manual calculation. This is the most accurate method, but it does take some time. Understandably most people prefer to use our on-line heatloss calculator, which performs a simplified heatloss calculation in a few minutes.
Our on-line calculator is available wherever you see the ‘on-line calculator’ symbol. To use it you need to know the length, width, height, type of insulation of your building and temperature you want to maintain.
Once you know how many kilowatts of heat you require divide this by the size of heater you have chosen to find the minimum number of heaters needed.
For instance if the calculator says you need 100kw, you would need 100/21 = 5 EA21 21kw heaters.
Example: A small industrial unit in the south of England measuring 8m by 15m and 3.5m high needs to be
maintained at 16C. The unit has cavity walls and a corrugated asbestos roof.
What if I don’t do a heatloss calculation?
It is impossible to choose a heater until you have done a heatloss calculation. To aid you we have provided a free on-line heatloss calculator and step by step guide to manually performing heatloss calculations.
It’s your responsibility to ensure the heater(s) you order are big enough to heat your building. You cannot return a heater because it is too small for your application. If you have any doubts about the size of heater you need, contact a local heating engineer for advice before you order.
Are space heaters suitable for my building?
Disclaimer: Our heat-loss calculator is a simplified tool designed to provide a quick calculation of
heatloss for typical buildings. It is not intended to be used for ‘special cases’ i.e.
buildings of unusual construction, where doors or windows are permanently open, or where there are large heat sources such as
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