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Local manufacturing — low-e windows for passive solar design in colder climate

homesteady | Posted in Energy Efficiency and Durability on

Hello All,
I have reviewed various posts and want to clarify some points…Thank you for any time you can lend my questions. You all have a wonderful forum here and I am a first time participant.

I am currently doing renovations and replacements for select window on a passive solar and adobe brick structure in high elevation New Mexico. All windows addressed are picture windows, uncased and basically framed and caulked into fixed position. Working on a DIY budget at a non-profit commune.

I am considering having windows fabricated locally in Albuquerque at a reputable glass shop that does auto and window fabrication. Am looking at 1/4″x1/4″ with a 1/2″ spacer for 1′ overall. Clear over Low-e with glazing on surface #3 for optimized solar gain and emissivity. They don’t do gas fill, but then I am at 7200 feet and I have read that gas fill is not that viable long-term at this altitude. The spacer has what I am assuming is a quality desiccant design.

Question 1…Is this spacing proportion of “1/4″x1/4″ with a 1/2″ spacer for 1′ overall” ideal dimensions for SHGC?

Question 2…
Is there any reason I shouldn’t have a local glass shop manufacture these windows when working on a tight budget?

I understand surface #3 is the best surface for my purposes for east, west and south exposure.
Question 3…Is #2 advisable for Northern exposure in elevated spaces prone to rising heat and heat loss, or will #3 suffice?

I understand that hard coat glass is ideal for my passive solar purposes…
Question 4…In the north facing windows prone to heat loss, should i get soft coat glass for greater emissivity?

Many thanks for helping me make these improvements with sage decision making. I understand that getting windows from a pro window company would likely be your highest recommendation, however, its not in the credit cards.
Many appreciations for your clarity,

GBA Prime

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  1. GBA Editor
    Martin Holladay | | #1

    I see no reason you can't order IGUs from a local shop. A 1/2-inch gap between panes is fairly standard.

    I don't have time to answer all of your questions right now -- I'll try to get back to this. In the meantime, you might want to read this article: All About Glazing Options.

  2. GBA Editor
    Martin Holladay | | #2

    While you can order IGUs from a local shop, you need to be aware that the lack of argon gas represents a significant performance hit. You might want to ask around to see if any manufacturers offer argon-filled glazing for delivery to your area. Depending on the elevation of the manufacturing plant, and the number of high-altitude passes between the plant and your building site, you may still be able to get IGUs with argon.

  3. GBA Editor
    Martin Holladay | | #3

    Ask the local manufacturer if they can estimate the SHGC and the U-factor of the different options. For north-facing glass, the SHGC isn't too important -- but you want the lowest possible U-factor.

  4. Expert Member
    Dana Dorsett | | #4

    For all but the south facing windows you may want to consider low E on surface #2 and a hard coat low-E on surface #4, which brings even air-filled units into the U0.25 range. They're still net energy gainers (even on the north side) but have a lower SGHC. Low SGHC for west facing windows can be an important summertime comfort factor in your location.

    [edited to add]

    Compare the SGHC & U-factors for both air and argon fill in the table labeled " Double Pane with LoĒ-i89 " on this page:

    The i89 on surface #4 is a hard coat low-E coating (probably indium tin oxide). The higher SGHC of their LoĒ-180 + LoĒ-i89 combination option probably makes it suitable for your high-gain windows too.

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