*Determine how many panes of glass are in the windows. Single-paned windows are the least energy efficient. You can replace them with double- or triple-paned windows to enhance energy efficiency and make a home more comfortable during all seasons.
*Look for condensation inside the glass on double- or triple-glazed windows. This could indicate seal failure.
*Do your windows open and close easily? If your windows are hard to open or close- or they won't stay open or locked- this could also be a sign that the windows need replacing.
* Have someone stand outside your window. With a small flashlight, stand inside and "travel" around the window's perimeter. If the person outside sees areas of light coming through, this is an indication of seal failure- and probably energy loss.
* Does it seem especially noisy in your house? Replacing your windows with better quality windows will help reduce noise transmission.