Window treatments block summer heat

June 23, 2020

In summer, unprotected windows suck in heat and create the heat gain that is so uncomfortable and expensive. Here are some ideas from the U.S. Department of Energy that can reduce energy loss through windows and improve the appearance of your home.

Weatherstrip and caulk — By far the most effective thing you can do is to stop air leaks. Simple caulking and weatherstripping are a do-it-yourself project for most homeowners.

Awnings — Window awnings can reduce solar heat gain in the summer by up to 65 percent on south-facing windows and 77 percent on west-facing windows. That’s amazing! You can use an awning to shade one window or have an awning custom made to shade the entire side of your house.

Choose an acrylic or polyvinyl laminate fabric that is water-repellent, resistant to mildew and fading, opaque and tightly woven. The lighter the awning, the more sunlight it will reflect. And make sure the awning has openings that release otherwise trapped hot air.

Blinds — Window blinds, vertical or horizontal slat-type, are more effective at reducing summer heat gain than winter heat loss. With interior blinds, you can adjust the slats to control light and ventilation. For example, when completely closed and lowered on a sunny window, highly reflective blinds can reduce heat gain by about 45 percent. Exterior roller blinds are usually made of wood, steel, aluminum or vinyl and mounted above the window. When you lower these blinds completely, their slats meet and provide shade. If partially raised, the blinds allow some air and daylight to enter through windows.

Drapes — A drape’s ability to reduce heat loss and gain depends on several factors, including fabric type (closed or open weave) and color. During summer, close drapes on windows receiving direct sunlight. Studies demonstrate that medium-colored draperies with white-plastic backings can reduce heat gains by 33 percent. Drapes also stay cooler in the summer than some other window treatments because their pleats and folds lose heat through convection.

Two drapes hung together will create a tighter air space than just one. One advantage is that the room-side drape will maintain around the same temperature as the interior space, adding to a room’s comfort.

High-reflectivity films — These films, which you can apply over existing windows, help block summer heat gain. They are best used in climates with long cooling seasons, because they also block the sun’s heat in the winter. Their effectiveness depends on size of window glazing area, window orientation, climate, building orientation and whether the window has interior insulation. Silver, mirror-like films typically are more effective than the colored, more transparent ones. East- and west-facing windows, because of their greater potential for heat gain, can benefit the most from these films.

Insulated panels — An insulating window panel or pop-in shutter typically consists of a core of rigid foam board insulation. You can push or clip it into the interior of a window. The panels are made so their edges seal tightly against the window frame. Seals can be made from magnetic tape or Velcro. No hardware, such as hinges or latches, is required. These panels have R-values between 3.8 and 7.

Mesh window screens — These screens can diffuse solar radiation, reducing heat gain in the summer. Screens should be mounted in an exterior frame and should cover entire windows. They are particularly effective on east- and west-facing windows.

Overhangs — Properly sized and installed roof overhangs can most effectively shade south-facing windows from the summer heat. If oriented properly, overhangs will allow the sunlight in through the windows during the winter, providing more warmth to a house. Adding overhangs to an existing house can be difficult and not always effective, so save this idea for a house under construction.

Shades — When properly installed, window shades can be one of the simplest and most effective window treatments for saving energy. Mount them as close to the glass as possible with the sides of the shade held close to the wall to establish a sealed air space. Lower shades on sunlit windows in the summer. For greater efficiency, use dual shades — highly reflective (white) on one side and heat absorbing (dark) on the other side — that can be reversed with the seasons. The reflective surface should always face the warmest side—outward during the cooling season and inward during the heating season, and they need to be drawn all day to be effective.

Shutters — Window shutters, both interior and exterior, can help reduce heat gain and loss in your home. Interior shutters need a clear space to the side of the window when they’re opened.  Properly designed exterior shutters may provide the best possible window insulation system. They usually include a mechanical crank, rod or motor to allow operation from indoors.

Like window blinds, louvered shutters work best for summer shading. Movable or fixed louvers allow ventilation and natural daylight to enter a room while blocking some direct radiation. However, they won’t provide much insulation against heat loss in the winter.

Storm panels — When added to a single-pane window, a storm panel can reduce winter heat loss by as much as 50 percent. Panels can be exterior or interior. Exterior panels can be singles that you put up in the fall and take down in the spring or combination, which consists of two windowpanes and a permanent screen over the window.

Interior panels consist of flexible or rigid plastic. They are easy to install and don’t have to be custom-made like exterior panels.

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