Is there one brand of vinyl windows that is more energy efficient and reliable?
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I have heard mixed reviews on various brands of vinyl windows. Additionally, our home has custom windows throughout. Are windows with dividers (used for aesthetics only) more or less efficient?
As a green architect, I usually do not spec vinyl. This is highly debatable in the green world -- on the one hand, vinyl windows save trees and paint and are lower maintenance than wood. When compared to aluminum-clad wood windows, the vinyl at least saves on wood, if not the other two.
BUT vinyl is horrible for the planet. Its production has been shown to cause cancer as it pumps carcinogens into the environment during production as well as during a house fire. Also, vinyl windows are not as readily recyclable when they have met their life expectancy and need to be replaced.
All of that said, I do realize that sometimes vinyl is the way to go -- usually for financial reasons. Windows are very expensive. The cost of a vinyl window can easily be half the cost of a clad window.
So, when we do spec vinyl windows, we spec a company called Paradigm. The reason we specify these windows is two-fold: they are actually made of ABS and not vinyl, and they are very energy efficient.
The difference between ABS and vinyl is that ABS does not contain chlorine, and therefore has no risk of dioxin generation during a fire or as the product is destroyed at the end of its life-cycle.
These windows get a U-factor rating of .20. This is extremely good. The U-factor (or U-value) measures the rate of thermal transmission (how well the window keeps warm in -- or cold in -- depending on your climate). Basically you get a federal tax credit if you achieve U.28 or lower (the lower the better). Most normal double-pane windows (of any kind: vinyl, clad, etc.) get U-factors of .30 to .38. You can easily get double-pane windows in the U.27 to .29 range. Getting lower than U.25 is great! There are even windows out there -- generally they are fiberglass or vinyl -- that get as low as U.14!
I notice that you are in San Diego, and the Paradigm windows are made in Maine and are not for sale in your region. I have been searching and am having trouble finding a specific vinyl window maker in CA that meets the same specs that Paradigm has. I would recommend that you call around to different vinyl window companies and ask what U-factors their windows achieve and whether their windows are made of vinyl or ABS.
You could also look into fiberglass. A fantastic option for fiberglass windows would be Serious Windows. They achieve great performance and most would agree that fiberglass is greener than vinyl. And they would be available in your area. (The price for these would be higher than vinyl.)
As far as the grilles in your windows -- your muntins -- you are right. If they "simulated divided lite" meaning there is a grille in the middle of the glass as well as on each side of the glass, then the overall energy rating of the window will be reduced a small amount. It is not negligible but it is also not a primary factor in reducing the energy efficiency of the window. For example, maybe the grilles would raise your U factor .01 or .02 points. Once you find a window company that you like, you can have them tell you the U-factor on the window if it does not come with muntins, and then have them tell you the same if it does come with muntins. And decide if you feel it is worth it.
As an architect, I prefer the simulated divided lite muntins or no muntins at all. Aesthetically the look and feel of the interior or exterior snap-on grilles rarely work well and in the green world you might call those "legs on a snake" (a complete waste of materials and energy)!
Good luck with your project.