TODAY'S TECHNOLOGY AND YOU

New window films stop summer heat

Q: Dear Jim: My windows are in good shape, but I want to block the heat and glare and reduce furniture fading. Will installing clear insulating do-it-yourself window film help much and also save energy during the winter?

-Meg H.

A: Dear Meg: When people think of residential window film, they often mistakenly think of the huge reflective glass office buildings that resemble mirrors. Actually, the most energy efficient residential window films have only slight reflectivity and tint. If you were inside a room with insulating window film installed, you would not even notice it.

Applying window film yourself or having it professionally installed is an excellent solution to minimize overheating, glare and fading. You will also be surprised at how pleasant it is to be in a room without harsh glare from windows. Instead of drawing the curtains or blinds and switching on a lamp, which uses electricity, you can often leave the curtains open and the lamp off. Using lamps during the summer also creates more heat your air conditioner has to run longer to remove.

With normal window care and cleaning, the new residential window films may last 10 to 15 years. When you consider the year-round energy savings and resultant lower utility bills plus the longer life for furniture, curtains and carpeting, applying insulating window film can easily payback its cost.

Some manufacturers offer only do-it-yourself or professionally installed window films and others offer both. The primary difference between professional and do-it-yourself films is the type of invisible adhesive used to fix the film to the window. Professionally installed film usually has a fairly long warranty. You can purchase special adhesive dissolving solution to use if you later decide to remove the film.

Many of the newer residential window films, especially the do-it-yourself insulating film kits, are nearly clear. Typical color choices for the lightly tinted films are platinum, gray and bronze. Even with just a slight tint, they can block more than 50 percent of the

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total solar energy that hits your windows.

The new insulating window films function in a similar way to new efficient low-emissivity (low-e) replacement window glass. To create the low-e properties, a microscopically thin layer of metal is deposited on the film. This layer is so thin, visible light passes through it and it appears to be totally transparent. Window film is actually made of many layers and the metal film is deposited on the inner layers for protection.

Heat energy is a different wavelength than visible light and the thin metal layer is less transparent to it than to light. In this way, it reduces heat flow through your windows without interfering with the view. During the winter, the metal layer reduces heat loss from indoors, so your heating bills will be less. Your comfort, especially when sitting near a window on a cold day, will also be improved.

If you apply this insulating film to all of your east-, west- and south-facing windows, the reduction in your air-conditioning electric costs will be noticeable. Not only will the film block heat, but without the intense radiant heat and glare from windows, you often can be very comfortable with the thermostat set several degrees higher. This can result in up to a 10 percent electricity savings.

The clear plastic material used for the film naturally blocks almost all of the fading ultraviolet (UV) rays, but furniture and curtain fading has other causes such as visible light and heat through windows. The amount of tint and other solar properties of the film decrease these other causes of fading.

If you can wash a window, then you can easily install insulating window film yourself. You can purchase the film in pieces from a roll or already prepackaged and a simple installation kit. Most films have a water-activated adhesive on one side. Thoroughly wash the window and leave it wet. Wet the film, place it over the window and squeegee it flat to the window. Cut off the excess around the edges and let it dry.

Although they look identical at the home center store, not all window film kits perform the same. Be sure to compare their properties - emissivity, shading coefficient and visible light transmission.

Lower emissivity films are best for year-round comfort and savings. Lower shading coefficient films block more heat. Lower visible light transmission films block more glare, but can make the window darker. All window films make glass shatter-resistant for safety during storms or around your children.

Write for (instantly download - www.dulley.com) Update Bulletin No. 617 - buyer's guide of seven window film manufacturers (plus a small piece) listing year-round insulating and sun control properties, colors, prices and DIY installation instructions. Please include $3.00 and a business-size SASE. James Dulley, Illinois Country Living, 6906 Royalgreen Dr., Cincinnati, OH 45244

James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.

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