Windows account for only about 10 percent of typical air leakage in your house according to the U.S. Department of Energy’s Energy Savers program. That draft of cold air around the latch may be as easy to solve as just locking the window to pull it snug into the frame. If locking the window doesn’t stop the leak, the problem may have another source -- and solution. Be prepared to investigate before making assumptions on the source of the draft, though; cold air travels as it falls and clings to cold glass and metal.
In the campaign to save energy, leaky windows rank lower on the list of priorities than, say, insulating the attic. Leaky windows do, however, cause drafts and waste energy. Tracking down the source of a leak at the latch of a window may not win the war but it can contribute to success during this winter’s battle.
Sash window structures have one or two movable windows with one or more panes of glass in each. Glass is secured in each pane with window caulk. Dried or cracked caulk near the latch on the top pane will admit cold air that rolls down over the latch. If the lower pane is loose, or cold winds rattle the sash in its channel, cold air can enter between the sashes. Check the panes for dry caulk -- it will crumble when tapped -- then clean, re-point and re-caulk the drafty panes. If locking doesn’t secure the lower sash, put a vinyl tension seal, or tubular vinyl or a sponge, inside the sash channel or between the sashes.
Metal casement window frames used in older homes can rust from condensation on the insides of cold metal frames. If you have a home of this vintage with drafts around the handles and locks, check the windows and caulking for damage from rust. Insulate the window frames with tubular vinyl and push rope caulk -- an inexpensive, easily removed insulation -- around the lock bases to seal any holes that have rusted through the welding. Modern vinyl casement windows seal more tightly, and some tubular vinyl along the side with the latch should seal the window.
The draft that you experience at the window lock may have traveled from elsewhere in the window, so track its source down. Cold air infiltrates non-insulated window frames and falls out along the window panes down over the top of the bottom sash. If your windows have counterweights, resolve to replace them with spring systems and fill the frames with foam insulation next summer. In the meantime, use inexpensive pulley seals to cover the holes where the ropes loop over pulleys -- and cold air filters in and cascades down. If nothing else works and the leaks create cold drafts, you may need to consider adding storm windows next year or placing shrink-wrap insulation on your leaky window this winter.
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