This heat loss calculator gives a guide to the approximate radiator size or wood burning stove output needed to keep a room warm on a cold day. It produces a breakdown and total of the surface and ventilation heat losses for a specific room in kWs (Kilowatts) and BTUs (British Thermal Units) so is hopefully one of the best btu calculators available.
The pull down menus for materials assume u-values for a typical home built before 1990. From the 1990’s onwards Building Regulations insulation standards have been gradually tightened so in these cases it is better to manually enter u-values prevailing when the house was built. See Building Regulations And U-values: How have they changed? for greater detail.
Scroll to the bottom of the page to find out more about using the calculator.
Heat Loss Calculator
How to use the heat loss calculator
Select the type of room and choose either metres of feet for dimensions. Enter room dimensions. Where the room is not a pure rectangle then just adjust dimensions to reflect the overall room area. Then enter information about the walls using the pull down menu or alternatively enter specific u-values if you know them.
To identify particular walls assume wall 1 and wall 3 are the longer walls (length) and wall 2 and 4 are the shorter walls (width). Entering a u-value overrides the information in the specific pull down menu. Enter the approximate window and door area in each of the four walls; if there are no windows/doors in a wall then just leave blank. For the windows, doors and ceiling select the material type in the same way. Then choose the ventilation adjustment. When entries are complete press the calculate button and the calculated heat loss and energy required in kWs and BTUs will appear below.