Window Films Block Solar Heat

Window films are applied to the inside of your existing windows to reduce air conditioner costs. These self-adhesive reflective layers stop much of the solar heat entering your windows. This reduction in solar heating can help reduce the cost of operating your air conditioner. The heat-blocking ability of window films is measured by their “shading coefficient”. Lower shading coefficients mean less solar heat gain.

Window films work best on the windows that the sun strikes directly. These may be east- or west-facing windows where low-angle morning or afternoon sun comes directly into your home, or south-facing windows if your home doesn’t have roof overhangs or trees to provide mid-day shade. Window films are especially effective if you have large picture windows or a sun-room that overheats.

If you choose to install window films, follow the manufacturer’s instructions which may include the following steps.

Clean the windows thoroughly. Use window cleaning solution to remove as much dirt as you can, and remove any paint or hard water deposits with a razor blade. Do a final wash with more solution.
Use a tape measure and sharp knife to cut the films to fit. Start at one edge, and peel back just a corner of the paper covering the self-adhesive backing. Once you’re sure that you have it square, remove the rest of the backing and roll the film out so that there are no trapped air bubbles. A squeegee works well to press the film into place.
Use a clean rag to rub the film down firmly. If you create any bubbles under the film, use a sharp needle to poke a small hole in the bubble and push the air out.
Be careful when cleaning window films – they are softer than glass and can be scratched.

Some window films block light as well as heat, and these reduce glare while darkening the room. Check the manufacturer’s specifications to find films that have a high or low “Visible Transmittance”, depending on whether you need to reduce glare or not.

Both Your Home Cooling Energy Guide and The Homeowners Handbook to Energy Efficiency have extensive information about maintaining comfort and reducing air-conditioning costs. See also Commercial Window Treatments.