Image Credit: Inline fiberglass
More Q&A Spotlight
There’s no doubt that windows are getting better — much better. The double-glazed, low-e units that looked so ground-breaking a few years ago seem merely ordinary now that Canadian, European and some U.S. manufacturers are producing high quality triple-glazed units.
Triple-glazed windows offer substantial benefits, including improved indoor comfort and lower energy bills.
But they aren’t cheap. Homeowners who are already facing painfully high building costs have to weigh the costs against the benefits. Are triple-glazed windows really worth the added cost?
Jon Wyman recently posed this question in a Green Building Advisor Q&A as he weighed the benefits of an upgrade for a double-wall house in western Massachusetts.
Wyman had already been planning to use triple-glazed windows in most of the house but was looking at another $4,800 up-charge to put triple-glazed units in the rest of the openings.
Marvin triple-glazed windows, with a U-value of 0.24 and a solar heat gain coefficient of 0.31, would cost $963, compared with $583 for Marvin’s double-glazed units with a U-value of 0.33 and an identical SHGC.
Sorry, no simple answers
Fuel costs will be lower and the house will be more comfortable with all triple-glazed windows, writes GBA senior editor Martin Holladay. That much is a given.
But the real question, he adds, is whether lower energy savings can be quantified? “You’ll need to use energy modeling software to answer that question,” Holladay says. “It would be necessary to model your home with the two options, and compare the energy use data.”
Christopher Briley agrees that energy modeling is the only reliable way to compare double- and triple-glazed window performance. Even offering a gut reaction is tough, he adds, without knowing more about the design of the house and whether windows are primarily for heat gain or for admitting daylight.
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6 Comments
Replacement Windows vs New Construction- what's appropriate
I totally agree with your closing statement about insulation and windows.
Window frame in article
Nice looking Fibreglass frame.. It's also a face seal glazing design with no drainage under the IGU. The drainage path would be into the foam insert. the jamb extension precludes gettin a good air seal around the perimeter at the back of the frame where it belongs. Foaming around the window for an air seal is problematic , ask the people in Toronto at window wise when they had tests done on a set of foamed in windows and they all leaked and took remedial work after the tests found the leaks.
The jamb extension also moves the window out in the wall assembly, makes it harder for room warm air to get to the window and warm it. A well insulated window will loose heat slower than a poorly insulated one, BUT it still looses heat and with out a source of makeup heat it will get cold, possibly down to the dew point for the air adjacent to the window. So keep the window in as far as you can and make sure it gets a source of heat to balance the heat flow to the exterior.
triple glaze
Move SOUTH!!!
Triple glazed is SO old fashioned - Get SERIOUS
There was a "This New House" where Amy Matthews talked to the Serious Windows CEO and their 5-layer windows are clearly superior with insulation qualities of an insulated wall. They are rebuilding all the windows in the Empire State Building without replacing all the existing panes of glass. VERY GREEN!
SHGC
I have to ask - shouldn't the Solar Heat Gain Coefficient selection be higher? 0.31 is very low in a heating dominated climate. I"ll bet a 0.5 would provide significant benefits in reducing heating costs across most of the year, and be no more expensive.
Response to John Gant
John,
I agree. When I provided recommendations in my article, All About Glazing Options, I suggested that a triple-glazed window for a cold climate should have a whole-window SHGC of 0.33 to 0.47 (or a center-of-glass SHGC of 0.50 to 0.63).
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