While we encourage draught-proofing and insulation to make our homes more comfortable and energy efficient, it is critical that there is adequate ventilation, especially if you’re using an appliance that needs oxygen to burn, such as a gas fire, boiler, gas stove, wood-burning stove or open fire. All of these need a surprising amount of air for combustion to happen efficiently. Air only contains 20% oxygen so appliances need a large volume to make sure they get the oxygen they need. Otherwise the combustion will be incomplete resulting in carbon monoxide which as you will be aware is very dangerous and can be a killer.