Stove heat output is measured in KW (Kilowatts). The most common KW output is 5, as this output suits most homes and requirements. There is a calculation which you can do to give you an idea (Length x Width x Hight Metres divided by 12). It is important to keep In mind though that you need the physical size of the stove to also work proportionally to the opening that will accommodate the stove. The stove does not want to look lost in the opening or crammed in with hardly any space around it.