We have designed this user friendly BTU calculator to allow you to easily calculate your heat output requirements for both central heating systems (in BTUs) and electric heating (in watts).
Simple sliders (fully compatible with tablet devices) give results as you go, so you can see how each variable is affecting the overall heat requirement results.
We give you the option of 2 different metrics: feet or metres (as everyone has their own preference).
The 3D model displayed underneath the calculator will change to represent the shape of your room (note: this may only appear 2D on some older browsers).
On completion of each room’s heat requirements you can save the results or print them out for your reference.
Further Notes about our Calculator
Calculating the heat output from your radiators or heated towel rails is the most important aspect of the purchase. You want the confidence that when you install your new designer radiators that they won’t only look great, but also provide the functionality of heating the room. We have spent a long time preparing this online calculator to ask you in depth questions about your room to mix together the most important variables to arrive at a professional BTU / Wattage requirement.
Remember when your house was built the builder will have spent time choosing the right radiators taking into account how the house was built. Therefore it is also a good idea to calculate what heat your existing radiators are giving. On our “Guide to Central Heating Radiators” page we have a list of all the different size standard panel radiators and what heat output each one gives, so please use this as guide.
We always suggest aiming to capitalise on the figures you arrive at. If you know you have a cold space, aim to purchase a radiator or towel rail which is slightly above the BTU calculator’s suggested heat output.
Some heat requirement calculators will give different requirements as they may be taking into account different variables to arrive at the final figure. There is no definitive science to calculations but you can rest assured that we have spent a long time on the mathematics at work in the background to give you accurate results from this BTU calculator. Be wary of other online calculators with a very simplified list of questions, as these may not take into account enough data about your room to give you the best suggestions for what heat is required.
BTUS: Plumbers will often specify the heat output you'll need for central heating systems in BTUs and this figure will normally be up in the 1000s. BTU stands for British Thermal Units and is a basic measure of thermal energy, where 1 BTU is the amount of energy needed to heat 1 pound of water to 1 degree Fahrenheit. The figures are so high when specifying BTUS for radiators as they are heating enough pounds of water to warm your whole room.
Watts: More commonly used for electric heating. You may also hear kilowatts mentioned, simply remember a kilowatt is equal to 1000 Watts. 1 watt of heat output is equal to 3.41 BTUS, so watts will always be the lower figure of the two scales. Typically electric radiators & electric heated towel rails are measured in watts, due to the fact they use electric as the energy source and electric is often referred to in watts.
Alex Ramsay, general manager comments: “If you have any further questions about the results please contact us and we will be happy to discuss your requirement with you. Be confident that with Geyser you are dealing with a professional company who specialises only in heating, therefore we have the in depth expertise in this field and the know how to give you accurate radiator heat requirement information.”
Electric Heating vs Central Heating: You'll notice that the suggested requirements differ from central heating to electric heating. This is based upon the differing technologies used to produce the physical heat within the room. Please ensure you select the right heating type above for your intended installation (ie. central heating or electric heating).
Please Note: The heat requirements given here are purely a guide, taking into account many varying factors as you can see. You can safely vary your heat requirements to select a suitable radiator by up to 500 BTUs/150w either way (1000 BTUs/300w either way if the suggested requirement is above 5000 BTUs).
Please Note: If you require very high outputs for large areas you may need to consider installing 2x radiators in the room to suffice, dependent on your chosen style.