Air Leakage

Air leakage, or infiltration, describes the air flowing through and around parts of the sash and frame of windows.

This is all driven by pressure. The potential for this leakage due to pressure build up is dependent upon the differences between the inside and outside atmospheric conditions. This is evident when it is very hot outside and cooler inside, and vice versa.

In the summer, outside air coming in brings heat from outdoors into the building. Cooled inside air is lost to the outdoors.

The incoming air can also carry moisture, which is trapped inside the wall and raises the humidity level in the building.

During winter, the opposite occurs. Heated air is lost to the outside, and cold air is drawn in from the outside.

Other pressure effects are less apparent. In a heated building in winter, the “stack effect” creates higher pressure at the top rather than the lower levels as the warm air rises within the building. This pushes air up and out of the cracks at the top of the building, and draws it in at the lower level.

Heating and cooling duct systems and ventilation fans also create pressure differences by pulling air from one part of the building and re-directing it to another area.

Doors and windows can be a pathway for air to be pulled in or pushed out by these pressures.

When properly installed, the airtight window products from Green Energy Windows will help control pressures within the building and prevent the leakage of air.

Note that the cracks and gaps will expel more air when the building is under greater pressure: as in the case of strong wind and driving rain, or the extreme temperatures of both hotter and cooler seasons.

Associated problems of air leakage:

• Heat loss in winter

Heat gain in summer
• Occasional increased indoor humidity in summer, which in turn increases cooling requirements.
• Drafts and discomfort for the occupants
• Higher utility bills

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