Air Infiltration

The process that carries heat through cracks and gaps around window frames. Infiltration through leaky windows can carry cold air into a house and carry warm air out. Infiltration is driven by wind and other differences in air pressure, such as warm air rising inside a house.

Windows vary dramatically in how effectively they block infiltration. Air tightness is usually measured in cubic feet of air per linear foot of crack (cfm/ft) at specified testing conditions. The tightest windows have air leakage rates as low as 0.01 cfm/ft, and the industry standard is 0.37 cfm/ft. Most of the better windows have leakage rates in the range of 0.01 to 0.06 cfm/ft.

Window technology has improved dramatically in recent years, with the net result of lowering your energy bills.

Why Replace Your Old Windows?
"Over 40% of a home's energy loss is through windows and doors."

Air movement through sash and frames wastes energy and money.  A 1/16" gap around a window = 1 brick 12 windows with 1/16" gaps = 12 bricks