This article comes from energy.gov
How to Keep Your Home Cool With Window Treatments
Window coverings can reduce energy loss through the windows, cooling bills, and improve home comfort. Use these tips to lower your energy bill this summer:
Operable Window Coverings
Operable window coverings give you the flexibility to choose whether to keep your window coverings open or closed for privacy, and to maximize natural light, take advantage of heat from the sun in the winter, and reduce heat gain in the summer. Options include shades, blinds, draperies or curtains, and some shutters.
Not all window coverings are operable, but of those that are, one study found that 75% of residential window coverings remain in the same position every day. If this describes your habits, be strategic about which coverings you open in the morning.
In the summer, you may want to keep certain window coverings closed to reduce heat gain. For natural light, open those coverings that don’t get direct sunlight.
Insulated Cellular Shades
Insulated cellular shades are made of pleated materials that are designed to fold up, accordion-like, usually at the top of the window, but sometimes at either the top or the bottom. Insulated shades contain one or more air layers in a honeycomb cross-section. Some can be adjusted from the top or the bottom.
Insulated cellular shades are typically considered to have the highest R-values of all window coverings. The air pockets in the honeycomb cross-sections act as insulators, increasing the R-value and reducing the conduction of heat through the window.
Insulated cellular shades can be a good choice if you are looking for significant energy savings from their window coverings, as well as comfort, privacy, and increased home resale value.
In cooling seasons, cellular shades can reduce unwanted solar heat through windows by up to 80%, reducing the total solar gain to 15% or less when installed with a tight fit.
Window quilts have a sheet of quilted material that can be opened by rolling and closed by unrolling. They typically fit snug against the trim, either on tracks or with an attachment such as Velcro or snaps.
Because of their snug fit, window quilts offer R-value increases similar to cellular shades, and they typically cost less.
Roller or Roman Shades
Roller shades are usually inexpensive shades that are raised or lowered from a roller bar fitted at the top of the window. Roman shades are fabric window shades that are drawn up into a series of evenly stacked folds when raised or lowered.
These shades typically fit inside of the window casing, or just outside, and they come in a variety of fabrics, colors, and weaves. Heavier fabrics will typically offer slightly better thermal performance, but roller and roman shades offer only a small amount of insulation and are most effective for privacy, room darkening, and blocking sunlight.
Curtains and Drapes
Curtains are fabric interior attachments that are sized to fit the window, while drapes reach all the way to the floor.
A drapery’s ability to reduce heat loss and gain depends on several factors, including fabric type (closed or open weave) and color. With such a wide variety of draperies available, it’s difficult to generalize about their energy performance.
During summer days, you should close draperies on windows receiving direct sunlight to prevent heat gain. Studies demonstrate that medium-colored draperies with white-plastic backings can reduce heat gains by 33%.
To reduce heat exchange or convection, draperies should be hung as close to windows as possible and fall onto a windowsill or floor. For maximum effectiveness, install a cornice at the top of a drapery or place the drapery against the ceiling. Then seal the drapery at both sides and overlap it in the center. You can use Velcro or magnetic tape to attach drapes to the wall at the sides and bottom. Taking these steps may reduce heat loss up to 25%.
Two draperies hung together will create a tighter air space than just one drapery. One advantage is that the room-side drapery will maintain around the same temperature as the interior space, adding to a room’s comfort.
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