How Window Cracks Affect Efficiency

QUESTION:

Will a small crack in one pane of a double-pane window affect the window's efficiency?

ANSWER:

If the window was filled with an inert gas (argon or krypton), the gas will seep through the crack, causing some loss in the window's overall efficiency. However, assuming the crack is very narrow and does not allow a significant amount of air infiltration, you'll still benefit from the insulating value provided by the dual panes and space of relatively "dead" air. So your actual energy-dollar loss typically will be small—probably no more than a couple of dollars per year. From an efficiency standpoint alone, the losses resulting from the crack would probably be too small to justify the cost of repairing or replacing the window.