When two people sleep for seven hours, their sweating and breathing produce approximately 7.5 to 8 decilitres of moisture and about 150 to 200 litres of carbon dioxide. They also release some 250 to 300 watts of heat to indoor air. If the moisture content of indoor air rises too high, the moisture condensates in the windows or in the structures of the cold external wall. Structures that have become moist are breeding grounds for microbes and mould fungi, which will before long cause damage to the structures. Almost all fungal mycelia grow at a relative moisture of more than 80% and in normal room temperature. Efficient ventilation removes the carbon dioxide and moisture load as well as smells, taking them out of the house.