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Sunday, August 18, 1991 - Page updated at 12:00 AM

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Home Clinic

Does Broken Seal Reduce Insulating Value Of Windows?

HOME CLINIC: I was shocked to discover that after 10 years our double-paned insulated windows developed broken seals. I can tell that the seals are broken because I see a little bit of fogging between the panes. No one ever mentioned this problem to us when the windows were installed. Are there any brands of double-paned windows that last indefinitely? Also, does the broken seal reduce the insulating value of the window? - G.R., Vashon Island

DEAR G.R.: We're sorry to hear about the broken seals on your insulated windows. According to Jon Dalberg of Alpine Industries, broken seals may reduce the insulating value of the window somewhat, but not significantly. The biggest drawback is the fogging between the panes. Sometimes this is only noticeable in the mornings, then disappears the rest of the day. Other times, it is foggy throughout the day.

Windows get their insulating value by trapping air between two well-sealed panes of glass. Some insulated windows are actually filled with argon gas which provides a higher insulating value. When the seals break, moist air enters the space. However, as long as there is minimal air movement in the space, the insulating value remains high.

Broken seals are caused by buildup of water and other debris (pine needles, dust, etc.) in the window frame. Temperature differences between the indoors and outdoors also puts stress on the seals by causing them to expand and contract in cold weather.

In the early 1980s when your windows were installed, most companies offered a five-year guarantee. Windows manufactured today are far superior to earlier models, machine made using improved sealants and weep-hole designs that allow the frames to drain water properly. Manufacturers now offer lifetime warranties on many of their insulated-window products.

The best way to deal with your broken window seals is to contact the supplier or manufacturer. If the product warranty is still in effect, they may replace the units at a lower cost. Remember that there is a difference between product warranty and labor warranty. If the warranty has expired, unfortunately, there is nothing you can do to repair the sealant or add a moisture absorber that will have any long-term effect. Your choice is to live with the fogging or replace the new units.

HOME CLINIC: When I shut down my pellet stove for the summer, I vacuumed the fly ash from all the surfaces and cleaned the ash tray. Is there anything else I should do? Is it all right to leave the wood pellets in the hopper?

- C.B., Federal Way

DEAR C.B.: You're off to a good start. Vacuuming the fly ash and cleaning the ash tray are a couple of important steps to take, but there are more.

First, take the pellets out of the stove. They can absorb moisture in humid weather and cause rust on the metal stove parts. Also, wet pellets may not burn that well this fall. Second, remove fly ash from every surface of the stove. If left to build up, it can block air flow. Since it sticks to surfaces, fly ash should be removed with a small brush. A vacuum cleaner with special attachments works well for hard-to-reach places.

If your stove has the combustion blower downstream of the burn chamber, be sure to clean the impeller blades. Top-feed systems need to have the burn pot cleaned regularly. Removable pots or tools for stirring it make this possible. Heat-exchanger surfaces in all stoves should be cleaned as well.

Third, clean the chimney or exhaust system. Fly ash can collect in the chimney and block air flow. Creosote can accumulate as well. Clean the chimney with a chimney brush sized to the flue - 3-inch or 4-inch diameters are most common. After cleaning, joints and seams may need to be resealed with screws and sealant.

Finally, check the motor and blower to make sure they're adequately lubricated. Don't add oil unless they look dry or sound squeaky or rough. It's better to oil too seldom than too often.

Remember, each pellet stove is different. In addition to the steps above, your stove may have other unique cleaning requirements. Check your owner's manual - it's the better source of information for maintenance. If you can't find a copy, get another one from your dealer.

Home Clinic answers questions about home maintenance, repair and energy conservation. It is prepared by the Energy Extension Service, a division of the Washington State Energy Office. It appears Sundays in the Home/Real Estate section of The Times.

Copyright (c) 1991 Seattle Times Company, All Rights Reserved.

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