I have had a few questions lately regarding window air infiltration. This is an important component of energy efficiency but one that is often overlooked. Window manufacturers have their windows pressure tested at 75Pa. The result of the air infiltration test is listed on their window data as AI. The AI figure represents Litres per Second per square metre (l/s/m2).

As an example, a typical awning window and a typical double hung window might have the same thermal performance figures, (Uw and SHGC) but have wildly different air infiltration rates. Awning window AI = 0.3 l/s/m2 Double Hung AI = 4.2 l/s/m2 I have known of people who diligently selected windows with excellent thermal values only to have their curtains flapping (with the window shut) due to the high air infiltration…….not an energy efficient outcome.

LESSON! Make sure you consider air infiltration when selecting your next windows.