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Vinyl windows in passive solar house?

Jim Sweazey | Posted in General Questions on

I’m in Zone 6

One of my window distributers claims Vinyl windows can’t be used with high solar heat gain glass. He claims they will melt. I think I have seen evidence of light reflected off a window that melted vinyl siding and I met someone that had trouble when he put foam on the inside of a south window. But, I still have a hard time believing these windows would melt. What do you guys say?

I am considering Fibertec, Accurate Dorwin, and Duxton, all protruded fiberglass. WASCO and Prossimo vinyl. Any input would be greatly appreciated.

I have read the idea the no windows should be high solar heat gain but I think in my case it still makes sense. Most of my south overhangs extend 10 ft. to the east and west of the windows and I plan on pulling any excess heat from the second floor down a 14 in. duct to a basement high mass area under a masonry stove.

Thanks,
Jim

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jim,
    Your window distributor is wrong. It's possible to purchase vinyl windows with high solar gain glazing. For example, Pella offers its Pella 350 and Pella 250 vinyl windows with optional NaturalSun low-e glass with argon. ("NaturalSun" is Pella's name for its high-solar-gain glazing option.)

    More information here: Pella glazing options.

    -- Martin Holladay

  2. Stephen Sheehy | | #2

    Our Intus vinyl windows have a SHGC of .49. No problems at all after two years.

  3. Andrew Bater | | #3

    Jim, I live in a passive solar home with a lot of thermal mass and a masonry heater, so we are compadres.

    One of our south facing windows is a large tri-fold door assembly with Cardinal high solar gain glazing in it that sits underneath a roughly 10' overhang. I think I spent about $1000 extra to get that glass option. I doubt I will ever get that money back. Yes, there is the odd winter day where the sun streams all the way into that kitchen/dining room area totally delighting the cat because she can chow down and sunbath too. Really though it would have been cheaper to buy her a little heated mat instead; just not enough days in the year where the geometry works to have made that glass expense worthwhile.

    What worries me about south facing deep overhangs is that they can build up significant levels of heat. It can get darn hot outside on those south walls. Even with my only roughly 3' overhangs on the rest of the house we had to make special roof insulation and venting arrangements to prevent ice dams. Joe Lstiburek has an excellent discussion of this phenomena in his Structural Insulated Panel book. Would that kind of heat melt vinyl windows, can't say, but I would wonder.

    Oh and one more thing, insects love those deep south facing overhangs because they "extend their season". Every ladybug, wasp, stink bug and fly will think you are the best host ever!

  4. Jim Sweazey | | #4

    Thanks for confirming this.

    Andrew- My south overhang is 3' but there is a 10' porch to both the East and West of the house. As you know the overhang is not effective when the sun is rising and setting, missing the overhang but my overhang extends over the porches so it should be work better.

    Thanks again,
    Jim

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