The Energy Column - Window Efficiency

THE ENERGY COLUMN 2002

Now in its 16th year!
Written by: Ken Sheinkopf

Phone: 321-638-1007 Date: February 2, 2002
Fax: 321-638-1010 Column No.: 02-05
E-mail: sheinkopf@fsec.ucf.edu

Q.: "I’m a home inspector in Virginia and I saw a column you recently wrote in our local paper about the benefits of good windows in a home and what a good investment they are. I do not agree with your conclusions at all and have never seen an analysis that even suggests windows are a worthwhile investment. How do you defend this?

A.: Ouch. Don’t take this personally, but I went back to several energy researchers I know and each one disagrees with you. Strongly.

The general consensus is that while windows may not be the single most cost-effective building option to consider in a home, they are clearly one of the most important. And their desirability goes far beyond the basic energy savings you’ll get from a better window.

For some specifics, let me turn once again to nationally recognized energy expert Danny Parker of the Florida Solar Energy Center. Here are some of his comments on your letter and the various benefits he says windows offer.

1. Comfort. Higher performance windows (often with insulated glass and a low-e coating, either with or without solar control) greatly improve interior comfort (there is less temperature distribution from one room to the next). Comfort is, after all, why you are inside, rather than outside when it is 30 degrees outdoors or even 100 degrees! And when seated closely by standard windows instead of by high performance ones, you’ll really notice a difference. Why have a window seat no one can use in winter?

2. Condensation. Single-glazed windows or double-glazed windows with metal, non-thermally broken window frames cause water vapor to condense on the inside of windows during winter. The condensing water often collects at the bottom of the window sills, rotting out the sills or otherwise ruining the wall finish and sheetrock or plaster. Parker’s sister in California is changing all of her metal-framed windows in her home for precisely that reason. She is changing to better performing vinyl frames, although there are wood and thermally broken metal frames that would do the same job. Also, during nighttime in the summer, if windows are only single-glazed, moisture can collect on the outside when the glass surface falls below the dew point. This can also be damaging, although it has the added drawback of obscuring the exterior view.

3. Sound. Ever have somebody drive a lawn mower by a room with single-glazed windows? You would be amazed at the amount of sound-control that comes from double-glazed, insulated glass. Same thing for privacy. No reason for you to have to listen that closely to your neighbor's rowdy party at 2 a.m., or to that dog that won't stop barking.

4. Power Outages. If your home ever loses electric power, you’ll see for yourself that a home with thermally improved windows will take longer to get cold in winter and take longer to overheat in summer.
 

5. Glare. Solar control glass for otherwise fully exposed windows can help to control localized overheating and interior glare. Exterior shading is always better for both, though on two-story homes that may not always be possible.

6. Energy. Research has shown that better windows do save energy in addition to all the other things listed above. They also save most on peak, the times when the utility has the greatest trouble meeting the peak load. They also allow you to get by with a smaller heating or cooling system. When sizing the systems using Manual J, you'll often find that the heating or cooling system can be sized half a ton smaller than otherwise would be necessary with the lowest quality windows.