How many kW of heat output do you need?
To calculate the kW requirements of the space to be heated:
1. Measure the length, width and height of the room or area that you want to heat, in metres.
2. Multiply this by 0.07 to arrive at the nominal output required.
Lm X Wm X Hm X 0.07 = required nominal output in kW
If the stove has too little output for the room, it’s likely that it will be run too hot. A lot of the heat generated escapes up the chimney as the vents will be open wider than they should be. This is why "maximum output" figures are misleading, and have been replaced by 'nominal' figures.
All stoves’ nominal output in kW should be matched to the size of the room. All stoves should be run as near to their nominal heating output as possible, i.e. burning at a gentle rate with at least some flame.
If the stove is too big (too high a kW output) you’ll be running it with a slow, smouldering fire. This will create pollution as the gasses (smoke) escape un-burnt up the chimney. You’ll also be wasting money on fuel.
For Stoves with integrated boiler - The rating of the boiler output in kW should closely match the combined output of all radiators on the system.
1kW = 3,412 BTU/hr
If you expect the outside temperature not to go down to -1C or if the stove is going to be a secondary heat source, then you could use a stove with a lower heat output (e.g. for houses with central heating).
This calculation is the usual standard used and is for an outside temperature of minus 1 degrees C
The requirement could be higher if the room is poorly insulated, has thin walls, draughty windows, or a high ceiling, and vice versa.