To illustrate, an open fire attains just 15% output as a lot of heat is lost through the chimney. Nowadays a wood-fired stove or heater attains on average an output of around 70 to 80%. The emission of an open fire as opposed to a good wood-fired stove or heater is therefore much higher. When both are used to heat a space the open fire evidently has 15 times more CO emission than the wood-fired stove and 50 times more particulate emission than the wood-fired stove.