This or That: Curtains or Plastic for Insulating Windows?

Insulating windows is an easy and fairly inexpensive way to cut your heating bill. But which is most effective, curtains or those tape-on plastic sheets?

November 9, 2009

If you want truly energy-saving windows, the best alternative is to augment or replace them with Energy Star–rated products. However, new storm windows can be pricey, so the next best trick is to reduce heat loss. Draperies, blinds, storm windows, and shutters are all very effective at insulating your windows against cold drafts and heat loss. But this time of year, home-improvement stores tout an increasingly familiar alternative: plastic sheets that shrink with a blow dryer for a tight fit. Or should you invest in curtains or drapes?

This: Drapes


Pros: "With insulating drapes, some tightly cover the whole window so heat can't move around them, and the drape is offering insulation like a nice jacket," says Nils Petermann, manager of the Alliance to Save Energy's Efficient Windows Collaborative project. Under ideal conditions, insulated drapes can make a huge impact on heat loss by creating an insulating air space that keeps cold window surfaces from drawing heat out of the room. According to engineers at the University of Texas, adding insulated drapes to a double-paned window can reduce heat loss by 46 percent, and 58 percent for a single-paned window. Even noninsulated drapes will decrease a room's heat loss by 10 percent. As an added bonus, they reduce heat gain in the summer time, so your up-front investment will save you money year-round. The University of Maine Cooperative Extension service estimates that you could conceivably recoup your investment in insulated draperies within one to two years.

Cons: Improperly installed, draperies can actually add to heat loss. Gaps at the top of the drapes, along the sides, and at the bottom can create a tunnel effect, drawing heated air from your room to behind the drapes, where it cools as it comes in contact with a cold window surface. Correctly installed insulated drapes can also trap warm air next to a cold window surface, causing condensation problems that damage window frames or lead to mold problems.

That: Plastic Window-Insulation Kits

Pros: Plastic window-insulation kits are easy fixes for cold-weather problems, and some cost as little as $4 (though most are in the $8 to $16 range). They involve taping a solid sheet of plastic film over an entire window to create that insulating air space, and the entire project takes one afternoon.

Cons: "There's really no good information on how they affect heat loss," says Petermann, since they've never been independently tested for heat loss. In theory, they function similarly to drapes by creating a dead air space that prevents heat from escaping, however, their effectiveness hasn't been studied. And, although some of the films are made from low-density polyethylene (the same kind of plastic used in plastic bags), others are made from toxic vinyl, which contains hormone-bending chemicals called pthalates and could release toxic fumes during the application process (the plastic films must be heated with a hair dryer so they shrink to fit the window frame). Finally, you can try to save the plastic to reuse it the following winter, but if it gets torn, the plastic film has to go to the trash. If you bought the polyethylene film, it can be recycled anywhere plastic bags are recycled, but vinyl films can't be recycled and are destined to spend forever in a landfill or be sent to an incinerator, where they'll release more toxic fumes.

This or That?

Go with…This, draperies.

Draperies are more attractive than plastic film for insulating windows, and you'll be able to reap the benefits year-round, rather than just in the winter. If you can't afford the pricier insulated drapes, a standard thick-woven curtain will suffice. "Any drapes will help to some extent," says Petermann. "The heat from your body radiates to the coldest surface of a room. So if there's a cold window, that's where the heat radiates to." Drapes keep you protected from the cold surface, he says, and that makes you feel more comfortable.

There are tricks you can use while installing drapes, as well, that will cut down on condensation and that tunnel effect.

•  Hang them as close to the window as possible.

•  Allow them to touch the floor or the windowsill, and keep the sides sealed. Attach Velcro strips or magnetic tape to secure drapes to the wall, suggests the Department of Energy.

•  Install a cornice. Designed to hide unsightly drapery hardware, cornices (those boxlike window treatments that hang over the drapery rod) will eliminate that tunnel effect by preventing hot air from getting pulled behind the draperies. They also allow you to hang the curtains so they overlap when closed, providing extra insulation.

•  Make the most of free solar heat by opening the drapes on your south- and west-facing windows during the day to draw heat in, and closing them at night to keep heat from escaping. North-facing windows don't allow heat in, so it's best to keep drapes on those windows closed all day long.

•  Monitor for condensation. "Anytime you're trying to hermetically seal off a window, there's condensation potential," says Petermann, adding that condensation problems are another reason those plastic films can be bad news. Manufacturers claim that the films cut down on condensation, but a leaky window or improper seal could allow moisture in, and the only way to fix it would be to tear off the plastic. Generally, condensation on the inside of your windows means that the humidity level inside your home is too high. Use ventilation fans in your bathroom and over your stove, if you have them, and keep the lids on pots of boiling water while you cook. Line-dry your laundry outdoors rather than inside, and, if you absolutely have to use your clothes dryer, make sure it's venting properly.

If you decide that drapes are too big a hassle, or just not your preference décorwise, Petermann suggests honeycomb shades, which have insulated dead air space built into the blinds and cut down on heat loss. Roller shades and Roman shades can also create that insulated air space.

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