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Community and Q&A

Hunting for high SHGC

user-705006 | Posted in Energy Efficiency and Durability on

I am on the quest (again) to find triple glazed windows with a low U-value but high SHGC (equal to or greater than 0.35) – manufactured in the US.

Just got off the phone with Great Lakes Windows. They mentioned a brand new glass package that may give me the SHGC I want: Guardian IS-20

By following some of the Q&A’s as well as GBA blogs, I know of Guardian 75/68, which provides a high SHGC. But I have never heard of Guardian IS-20.

If anyone has, and/or if anyone has an option on the Guardian IS-20, I would love to hear about it.

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  1. user-788447 | | #1

    Give the folks at H-window in Ashland WI a call. They have been following some of the interest in PassivHaus and rep a PH German import window but also manufacture their own line.

  2. Mike Eliason | | #2

    it's really hard for me to consider anything under 0,50 to be 'high-SHGC'. i've been meaning to collate a list of high-SHGC glazing for a while...

    the guardian IS-20 has a U-value of 0.676? also, it doesn't appear to be triple pane... probably not the best solution...

    some NA options:
    Cardinal 179/180
    Serious 9
    Pilkington LOF EA2
    AGC Flat Glass Comfort E2

  3. GBA Editor
    Martin Holladay | | #3

    As usual, I need to remind everyone to define their terms. Are you listing the SHGC of the glazing or the window?

    In the U.S., the NFRC has (wisely, in my opinion) determined that SHGC numbers will be reported as whole-window numbers, not glazing-only numbers. A glazing-only SHGC of 0.59 might be only 0.42 when reported according to the NFRC whole-window method.

  4. Mike Eliason | | #4


    in defining high-SHGC, i am only talk about glazing. i don't agree that looking at whole window method is correct, because most glazing is interchangeable between window manufacturers.

    if i like a certain window frame, i'd much rather know what my options are in terms of glazing (and resulting energy calcs), rather than knowing the glass i want to use and then finding a frame that the numbers calc out correctly. i prefer apples-apples comparisons, and i find with NFRC, the whole window numbers don't really get at that. also, i've never in my life utilized an NFRC-sized window.

  5. GBA Editor
    Martin Holladay | | #5

    You wrote, "I am only talk about glazing."

    I suspected as much, which is why I tried to get people to define their terms to clarify the discussion. There is no reason arguing -- "My apples are $1.25" -- "But my apples are 95 cents" -- if one person is talking about the price per pound, and the other person is talking about the price per kilo.

    Most U.S. window shoppers are familiar with NRFC labels. If you want to talk about the SHGC of glazing only, fine -- just define your terms.

  6. NwiHW6GJNL | | #6

    I'm also looking for some Cear Glass double Pane windows for a gut remodel in Greenland, NH. We have numerous indoor plants that like their sun. Where can we find them local and cheap?

  7. albertrooks | | #7


    You may also want to take a look at Optiwin. We represent them in the Pacific Northwest and I'm really happy with how things have gone so far. They build a top quality german window and as such, can place any of the European Union glazing units in the frame. The EU IGU's offer the widest choices of the attributes that you list.

    You can find them at: I've been negligent and haven't got our company info up there yet but I'm guessing your in the mid-west and don't need it.

    Good luck :)

  8. user-705006 | | #8

    Thanks to everyone to chip in. I am aware of some of the German window imports (I am German and know them from back home), but would really like to find a 'locally' manufactured product - either from the Midwest or somewhere withing the continental US... It may be that I am not getting the same performance as with the imports, but that may be OK if the IGU will work in the big picture.

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