While some ventilation is essential for good health and the prevention of condensation, too much of it can cause discomfort and waste energy. In winter air leaks may account for 12 to 25% of winter heat losses in a house with an insulated roof.

Draughts cause discomfort by creating localised chilling, even if the overall room temperature is comfortable. If the draught is near the thermostat of a heater, the heater will operate at a higher setting than necessary and waste energy.

In summer, cross ventilation is important for health and comfort because it helps to evaporate body perspiration and remove moist air that would otherwise contribute to mould growth. However, when it is cooler inside the house than outside, draughts of hot air can cause discomfort. If the house is air conditioned, draughts can lead to excessive energy use in summer as well as winter.

Sources of Draughts

Air can flow through the smallest openings; gaps around doors or windows, and fixed openings such as vents, flues or chimneys are the most common sources of draughts Construction joints that leave tiny gaps can also be a problem. These occur at junctions between door and window frames and walls, at the edges of walls, floors and ceilings, and where pipes or ducts pass through the construction.