What Causes Drafts

Drafts are created when air passes from outside into your home, or if warm inside air exits the building structure. To form drafts, warm air needs to find a place to escape, like gaps in the window, and a difference between inside and outside atmospheric pressures. It only takes one small leak and your heating system will have to work harder to maintain a constant temperature.

There are four main causes of drafts. Wind, the ‘stack effect’, combustion and mechanical extraction fans. If you have more than one of these occurring at the same time, the effect of drafts will be dramatic.

Wind creates pressure differences and suction effects as it passes a house. The air inside is affectedby the difference in air pressures and gets pulledthrough the paths of least resistance – the gaps. Cold air replaces it and is felt as a draft. The overall design of the house and the amount of

trees surrounding the building structure can have a significant impact on how winds affect it.

With the stacking effect, warm air rises, creating a higher atmospheric pressure at the top of the house and a lower pressure at the bottom where cold air is sucked in. Combustion heaters like open fires and gas heaters create a similar effect by forcing the heat to rise up chimneys and smoke flues forcing lower pressurised cold air to take its place.

Ventilation fans like those in bathrooms and kitchens will not only force steam and cooking fumes out, but also the heat present in the room. Cold air is automatically sucked in to replace it. Fans that have no automatic closing mechanism provide another means for the heat to escape even when it is not operating.