In Search of the Most Energy-Efficient Windows
How do offerings from Serious Materials, Thermotch, Inline and others match up out there in the real world?
It seems like a very long time ago, doesn't it, that windows were considered simple building components? As long as they opened and closed and let in sunlight most of us were content. We know now that windows are anything but simple. They're an essential part of an energy efficient building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.; they must simultaneously admit sunlight (and a certain amount of solar energy — but not too much), minimize heat loss or gain, prevent drafts, and last a generation or two.
This week's Q&A Spotlight from Green Building Advisor starts with a simple question from someone looking for just such a window. Claire Anderson wondered about the experiences that GBAGreenBuildingAdvisor.com readers have had with windows from Serious Windows, Thermotech Fiberglass, Fibertec, Inline and Accurate Dorwin. "I'm having a difficult time," she wrote, "finding high SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. windows (with a U-value less than or equal to 0.30) for my passive solar home that are affordable."
As simple as it sounds, the question proved complex: Who makes a window with a high solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. (SHGC), for solar gain during the winter, that's also an effective insulator (low U-value equals high R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. ), and doesn't cost an arm and a leg?
So who's really tops? It didn't take long for GBA readers to dive in with their opinions.
Experience counts, but your mileage may vary
Among the most often mentioned high performance windows are SeriousWindows, manufactured by Serious Materials Inc. of Sunnyvale, California. The windows are made with foam-filled fiberglass frames, suspended films inside the glass, inert gas fill, and high R-values, common attributes in this category of uber efficiency.
Scott Heeschen selected Serious units for a south-facing clerestory and Marvin Integrity units for the rest of the house after getting quotes from a number of suppliers. He found SeriousWindows were the most expensive: about $60 a square foot for operable units and $40 a square foot for fixed units in the 725 series.
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Heeschen also considered Fibertec windows (made by Fibertec Window & Door Mfg. of Concord, Ontario), which were about $10 cheaper per square foot in both operable and fixed versions. While the price was attractive, Fibertec had no local dealers. Serious Materials was only about 10 miles from where he lived, presumably making it easier to get service if he needed it.
Fibertec's lower price was attractive to poster Boulder, CO, who "tried to save a few bucks" by choosing its windows over Serious Windows. But Boulder found poor customer service, fingerprints between panes of glass, and gaps in the mitered corners. Ken Huck also found Fibertec windows "not the highest quality," although they were much less expensive than another oft-mentioned brand, Thermotech, made by Thermotech Fiberglass FenestrationTechnically, any transparent or translucent material plus any sash, frame, mullion, or divider attached to it, including windows, skylights, glass doors, and curtain walls. Ltd (not to be confused with Thermotech Windows Ltd).
Andrew Henry found Thermotechs were a pleasure to install and came with high quality Truth hardware that drew the sash tightly to the frame in the awnings and casements he selected. The triple-glazed units did a much better job of keeping out a cold winter chill than the older Marvin double-hungs he had in the original part of the house. Heeschen, however, found Marvin's Integrity windows a step up.
Brent, however, was totally unimpressed with his Thermotech experience, citing unresponsive customer service and lackluster tech support. He found more to like with Inline and Heinzmann European windows.
Accurate Dorwin was another brand that wins rave reviews. "These were by far the best windows we ever had...tremendous strength and quality," writes Stan, adding that the service and installation experience was the best he'd had in 25 years of building.
In short, there are no absolutes for defining "quality" and no universal experience even with the same manufacturers. Anecdotal evidence from builders and homeowners varies. In addition to the window itself, how local distributors deal with potential customers is certainly a factor. Poor customer service can make a great window seem like a bad buy, while responsive tech support can cure a lot of ills.
A detailed explanation of performance features and how they relate to the German Passivhaus standards was the subject of an earlier Holladay blog at GBA. He also offers some details on Serious Materials products, which use multiple layers of Heat Mirror film instead of triple glass glazing, an approach that has some drawbacks.
How to sort it all out? Site-specific requirements are a good starting point. Then, in addition to manufacturers' web sites, visit the National Fenestration Rating Council. Its data should weigh heavily in making a selection.
Yes, but are they really 'green?'
The very advances that make high performance windows possible are in themselves off-putting because they suggest an endless cycle of buying and replacing as technology improves, one of several anonymous posters laments.
Anonymous was in the midst of replacing 100-year-old sash. His observation? Windows are not so much rebuilt and repaired these days, simply replaced.
"To my knowledge, no one manufactures a sash where when the glass seal fails, or the glass gets broken all you need do is go to your local hardware store and buy new glass. As for being green, the direction window manufactures have taken us appears to be contradictory. What are the energy costs of manufacture and how much oil is being consumed to manufacture all this plastic.
"In my opinion, green needs to take the whole picture into account, including manufacture, maintenance, and product life."
Although Anonymous worries he'd strayed off topic, Robert Riversong assures him he's right on target. "In fact, your complaint is equally applicable to almost every product we buy and use today," Riversong writes. "There is very little in the 'green' movement that is truly sustainable or earth-friendly or even sensible."
Riversong would have us ponder the thoughts of writer Wendell Berry, who suggests several criteria for the introduction of new technology, including requirements that new tools should be cheaper, smaller, more efficient than what they replace.
Tax credits and third-party testing
Homeowners are now eligible for a federal tax credit of 30% of the cost of energy efficient windows under the American Recovery and Reinvestment Act, but there's a catch. In addition to having a U-value of no more than 0.30, windows also must have a solar heat-gain coefficient of 0.30 or less, and that's a problem, as described by Holladay in an earlier post.
In cold climates, a SHGC of between 0.39 and 0.65 actually saves more energy. Low SHGC windows are a good choice in Florida to lower air conditioning costs, but elsewhere a high SHGC means more solar gain and lower heating bills in the winter.
It's difficult and in some cases impossible to find high windows with high solar gain potential, as our original poster Claire had found. Coupled with the federal government's bungled attempt to promote energy efficiency with the AARA initiative, homeowners are likely to install windows that will deliver second-best energy performance.
Finally, there is the issue of third-party performance testing, which backs up manufacturers' marketing claims and ensures homeowners are getting what they pay for.
While Thermotech Fiberglass Fenestration is roundly praised, Steven asks how come the company doesn't have its windows listed with the NFRC?
We did, says the company's technical director Stephen Thwaites, back in 1999 when we were part of Thermotech Windows. The company didn't renew in 2003 because "building officials weren't (and in our experience still aren't) looking for NFRC stickers. More importantly it didn't seem to matter to our customers either."
However, because of a Canadian rebate program, Thermotech Fiberglass will be rejoining fold, Thwaites writes.
A GBA expert speaks
We have invited senior editor Martin Holladay to provide an expert opinion on high-performance windows.
Martin Holladay's advice:
Cold-climate builders need windows with a very low U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. , a very high SHGC, and a very high VT. That magic window doesn't exist, so we have to spec our windows based on a series of compromises.
Although most of the Heat Mirror glazing (that is, glazing that includes interior plastic films) used in Serious Windows has a very low U-factor, these windows come with a couple of drawbacks: the windows have a lower SHGC than comparable all-glass triple-glazed windows, as well as a low VT rating. Some homeowners with Serious Windows have been bothered by the appearance of these low-VT windows; they can make everything look gray.
Most of the Canadian manufacturers of windows with pultruded fiberglass frames are knowledgeable about glazing options. As long as you specify high-solar-gain triple glazing, you'll probably be satisfied. (Aim for a window with a whole-window SHGC of at least 0.39.)
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