A bit of illumination on window films

House Doctor | Gary Dymski

July 8, 2004

I had an estimate for professional application of a window film to five skylights. I'm trying to reduce energy consumption, since our bills have gone up with the arrival of a new hot tub. The estimate was nearly $600 for applying film, which I was told would reduce UV rays and the transfer of hot and cold air through the glass. Is this a product we can apply ourselves? What can you tell me about applying window film to help insulate the home year- round? I love the sun and warmth in the winter, so I am a little hesitant. Shades can't be installed because of the screens. An installer said the tracks would prevent screens from being removed for repair or cleaning. Any suggestions? Also, we had the proper electrical line installed, and whenever the hot tub motor goes on the room lights dim. Is that normal? The electrician said the tub is pulling so much electricity that it is normal.

Marguerite Shannon, Huntington

Most major manufacturers of window-film products - 3M, Llumar and Solar Gard, for example - require professional application. However, you can make this a do- it-yourself project by purchasing window film from Gila Window Films, a division of CPFilms of Martinsville, Va. Gila's products can be purchased online at www .gilafilms.com or at Lowe's Home Improvement Warehouses. Gila's Web site includes installation instructions.

Window films are designed to do two things: improve the insulation properties of glass and filter the sun's harmful rays to reduce fading. For year-round protection and insulation, you probably want a heat-control film. This film retains 55 percent of indoor heat, reflects 70 percent of summer heat and reduces harmful UV rays by 99 percent. You'll still get the warmth you said you like in winter, but your glass will be a more effective insulator and offer energy savings. In your case, a heat-control film will reduce the amount of interior heat being transferred through the glass in winter and limit the exterior heat from coming through the glass in the summer.

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Other films are designed to reduce glare or fading and even increase privacy. Films usually are rated by how well they measure up to these three properties:

UV reflection: Reveals how well a film blocks ultraviolet rays. A higher number indicates more protection.

Solar-energy reduction: Indicates how much infrared heat and UV rays are filtered by the film. Again, a higher number is better.

Emissivity: The lower the emissivity value (a measure of the amount of heat transmission through the glazing), the better the material reduces the heat transfer from the inside to the outside.

The films are applied to interior glass and last about eight to 10 years. You must follow the installation instructions carefully, and the glass must be squeaky clean. Visit the Gila Web site for information.

Now, let's consider the drain your new hot tub puts on your electrical system. If your lights dim when a large appliance - an air-conditioning unit, for instance - clicks on, this usually is a sign that it's been connected to the same circuit. A large appliance should be connected to its own separate circuit at the service panel, since these units draw high currents at start-up.

If your hot tub has its own circuit, as your electrician indicated, a couple of other things could be happening. There might be a problem with the service feed coming into your home. Or your wiring may not be the correct gauge; it could have too much resistance so when a large current is carried, there's a significant voltage drop, which affects the lights. Or there might be a broken or corroded neutral wire. To be safe, I'd have another licensed electrician evaluate the electrical system.

E-mail gary.dymski@ newsday.com.