The clearest sign that a window needs weatherstripping, or needs current weatherstripping replaced, is when the window lets in a draft. From inside the house, hold your hand to the edge of the window. If you feel any air flowing in, it’s time to take action.

Weatherstripping generally fails when it comes loose, breaks away, or bends. Certain types—especially foam gasket weatherstripping—also cease to work after a few years of being repeatedly crushed under pressure.

If you can’t simply refasten weatherstripping to fix it, the easiest route is to replace it. When replacing weatherstripping on a window, it’s a good idea to replace all of the material, not just the damaged part.

For double-hung windows, install spring-type weatherstripping. Although installation takes some expertise and time, it’s less visible than other types. Nail the stripping to the window frame except at the bottom, where you’ll nail it to the sash.

If you have a wood casement, hinged, or sliding window, choose pliable-gasket weatherstripping. Install it in the channels and sash. Use compressible felt for warped metal or wood frames.

Keeping weatherstripping clean will extend its life. Periodically brush off loose dirt and clean the surfaces around it. As needed, wipe it with a soapy sponge, and rinse with clear water.