This article was originally published in the May/June 1995 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.



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Home Energy Magazine Online May/June 1995


An Entertaining Resource

During the course of editing and writing articles, I have used your magazine on several occasions as a source for reliable information on home energy use. I usually don't think of Home Energy as a source for humor, but I want to thank you for your article, Annals of Energy Auditing: The Case of the Refrigerator with Rounded Corners,(see Jan/Feb '95, p.37). I have passed it along to the other editors here, recommending they read it and laugh. Thanks again.

Jefferson Kolle
Associate Editor, Fine Homebuilding
Newtown, Connecticut

Foggy Window Syndrome?

I have noticed a surprisingly high failure rate among double-glazed windows. The seal fails and allows moisture to enter the space between the windows, leading to fogging. Sometimes it happens just a few days after installation and sometimes after a few years. The most frustrating situation is when it happens with the first window, and then its replacement (which has happened more than once with me).

Double-glazed windows have been around for a while, so I'm disappointed to see so many failures. Why haven't the manufacturers improved their quality control?

Gigi Rollin
Wichita, Kansas

Editor's Note: The glazing layers in an insulated glass unit (typically glass) are separated at the edge by a spacer system (often metal). The spacer and glazing layers on either side of it are adhered together by a sealant. The sealant system is designed to keep moisture transmission at ultra-low levels, thereby keeping moisture from migrating into the IG unit. If the sealant fails, however (due to poor spacer corner construction, spacer joint construction, failure of the structural seal due to aging, incompatibility of glazing materials with the insulating glass sealants, environmental extremes, poor quality control, or other reasons) moisture will migrate into the cavity and condense on one or more glazing surfaces when temperatures and relative humidities dictate. A seal failure indicates a loss of gas-fill (if the unit was filled with a low-conductivity gas to start) and may lead to the deterioration (aesthetic and performance) of a low-E coating. Otherwise, its impact is aesthetic, not energy related.

Failures garner much of the attention, but manufacturers have greatly improved their quality control, says Bill Lingnell, technical consultant to the Sealed Insulating Glass Manufacturers' Association (SIGMA) in Chicago. Reputable manufacturers are conscientious of quality, warrantee their products, and will replace them if they fail, Lingnell says. Consumers should look for windows meeting the requirements of organizations like SIGMA. For example, SIGMA members must meet ASTM test specifications (E773 and E774) that measure a window's ability to withstand extreme temperatures, moisture, and ultraviolet light. Products with an ASTM E774 performance level of CBA have passed one of the highest SIGMA requirements. The tests are conducted annually by independent testing laboratories.

Note that a 10-year study conducted by SIGMA showed that less than 3% of units which passed ASTM CBA tests installed in over a hundred sample buildings failed after 10 years. The majority of the failures were in about 10% of the buildings with many of the failures due to units sitting in water.

By the way, look for a new Consumer Guide to Windows in an upcoming issue of Home Energy.

Venting Attics Not a Whole-House Approach

The article Ventilating Attics to Minimize Icings at Eaves (HE Mar/Apr, '95 p. 35) draws the conclusion that icings can be avoided by sizing attic ventilation systems to maintain an attic temperature of 30°F when the outside temperature is 22°F. A better conclusion would have been that icings can be avoided if heat losses to attics can be minimized, keeping attics from ever reaching 30°F when the outside temperature is 22°F.

There is no doubt that adequate ventilation reduces attic air temperature. There is also no doubt that it adds to building energy loads if heat energy losses to the attic are not first fully addressed. While mentioned at the end of their article, attic air sealing, duct leakage sealing, and insulation problem corrections seem to be an afterthought.

With an eye towards energy concerns, a follow-up to their research would be to compare energy consumption data for the buildings in their study, pre- and post-attic ventilation retrofit. Their mechanical ventilation solution is not a whole buildings, systems approach. As a stand-alone measure, the addition of massive mechanical ventilation can also mean a massive increase in energy losses.

Steve Hines and Pete Emidy
Rhode Islanders Saving Energy
Providence, Rhode Island

Author's Reply: Simply minimizing heat losses, without ventilating, will not prevent icings for all attics. (Duct sealing and additional insulation were not an afterthought.) Dual thermostatic control of the fans kept them off most of the time, solving a serious problem without creating an energy hog.

Home Energy's Internet Address

Hey, putting Home Energy on the World Wide Web was a great idea! I particularly like the indexes and the cross-referencing of articles. You might want to give a more precise address for the HE Homepage, however, because it took me a while to find it in the Department of Energy listings.

Felix Meier
Berkeley, CA

Editor's Note: Yes, we should have given the full address for our Home page but, to be honest, it wasn't finished when the editorial was written.

If you go to:, and then work your way down through Energy Information Resources and then select the alphabetical listings, you will find Home Energy. Alternatively, you can go directly to the Homepage by entering:


Our electronic neighbors have lots of useful stuff, too, so it's worth surfing around in these homepages. Which reminds us that there is a minor error in the listing for Energy-Design Online (EDO). For a description of EDO services, send an e-mail message to

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