When it comes to a home’s energy loss caused by infiltration (places where air leaks in and out), old windows are serious offenders. If you can hear windows rattle on a windy day, feel drafts blowing, or see light between the moving parts, you can bet that air is flowing relatively freely from indoors to out, and vice versa. And, as the air departs, so does your home’s expensive heat or air-conditioning.

Though new windows generally have built-in weatherstripping, there is no guarantee that they don’t leak as well. Low-grade products or poorly installed windows may have defective seals. Or the weatherstripping gaskets may be damaged.

It pays to check all windows for air leaks. Even if you can’t see or feel the movement of air, infiltration may be occurring—just to a lesser degree.

How do you detect the subtle movement of air around windows? It's easy. Just hold a lighted candle or a piece of cellophane wrap near a window and watch for the flame or plastic sheet to move.