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Community and Q&A

Triple-pane windows

John Barbuto | Posted in General Questions on

Good morning Martin,

I have been reading your articles online regarding windows for homes and have learned a lot over the last month from you. I live in Toronto, Canada and in November 2012 I had all the windows replaced in my house, brick to brick triple pane windows 1″ and 3/8 with Cardinal low e 272 coatings on panes 2 and 4.

Immediately we noticed how grey the glass appeared compared to our old windows and that the house actually is darker than before. Of course the salesman failed to mention this to us prior to closing the deal. The specs on the windows are as follows from the energy star labels that the government provides:

VT .35
SHGC .20
U-Factor .18

With our old windows the furnace would not run as often during the day since the sun was heating the house, when I would check it throughout the day the thermostat was set at 68and the house would often go up to 70 or 71 on sunny days. Now with these new windows the house remains at 68 and the furnace runs even when the sun shines during the day.

I contacted the window company and they are willing to change the glass and now I would like your expertise. I am thinking of going with Cardinal low e 180 but am unsure whether to go with 1 coating or 2. Also, if I go with 1 coating, which pane of glass would provide the best combination of shg, vt and also keep the heat in the house at night. The contacted the people at Energy Star within the Canadian government and he has provided me with a spreadsheet with specs from the window company that I used with low e 180 coating on surface 2 as well as on surface 2 and 4.

Surface 2 with Cardinal low e 180:

VT .46
SHGC .40
U Factor .22

Surface 2 and 4 with Cardinal low e 180:

VT .42
SHGC .36
U Factor .21

In addition, my current windows use super spacers but the new ones they will use have xl edge spacers. This is because the glass with the low e 272 comes from Canada and the low e 180 has to be shipped from the USA. Is there much difference between super spacers and xl edge from a performance standpoint. I can recall the salesman telling me back in September that they recently switched to super spacers but in his opinion the fail rate for the seals is higher than the xl edge and thus preferred the xl edge.

Again and I apologize for being long winded but would you suggest 1 or 2 layers of low e 180 and on which pane of glass would be better for letting in the sunlight during the winter months as well as keeping the heat in at nighttime.

Thanks in advance

GBA Prime

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, I hope you have read these articles:

    High-Solar-Gain Glazing

    All About Glazing Options

    Choosing Triple-Glazed Windows

    Unfortunately, it looks like you chose your windows without following my advice.

    In "All About Glazing Options," I warned, "When the VT drops below 0.40, everything seen through the window begins to look a little gray."

    In the same article, I wrote, "If you are in a cold climate, you probably want a double- or triple-glazed high-solar-gain window. ... If you can spring for a triple-glazed window, look for these specs:
    A whole-window SHGC of 0.33 to 0.47. Higher is better than lower.
    A center-of-glass SHGC of 0.50 to 0.63. Higher is better than lower."

    Concerning glazing selection, the advice I gave in that article still holds. "In general, neither glass manufacturers nor window manufacturers have “branded” any particular type of triple glazing. As a result, those interested in triple-glazed windows are forced to compare U-factors and SHGC numbers."

    As an example of what is available, check the specs for available glazing options for Thermotech Fiberglass fixed windows on this web page:

    Thermotech sells a triple-glazed fixed window with the following specs:
    Glazing only specs: 0.63 SHGC, 0.65 VT, 0.16 U-factor
    Whole-window specs: 0.55 SHGC, 0.22 U-factor

    See also this page:
    Thermotech sells a casement window with the following whole-window specs:
    0.44 SHGC, 0.23 U-factor

  2. Jin Kazama | | #2

    Martin: would you happen to know from which IGU brand does Thermotech use in its windows ??

  3. Dan Kolbert | | #3

    As you know, Martin, I have been through the Thermotech wringer. I realize this is a general discussion of window technology, but after a brief moment of optimism that they would deal with some lingering warranty issues, I'm back to my previous hopelessness with them. They still seem to not understand that servicing their product is part of the deal.

  4. GBA Editor
    Martin Holladay | | #4

    On the Thermotech website, I don't see any indication of the glazing manufacturer. If you want to find out where their glazing comes from, you can always call up Thermotech Fiberglass and ask. Their phone numbers are 613-839-6158 and 888-930-9445.

  5. GBA Editor
    Martin Holladay | | #5

    I'm in the same boat you are. About 4 months ago, Stephen Thwaites of Thermotech gave me his personal promise that he was sending me a package with window parts to repair my windows. I never received the parts.

  6. Forrest Twombly | | #6

    I’d just like to chime in with another recommendation of a window manufacturer to avoid: Inline Fiberglass of Ontario, Canada. The quality of the glass is decent, but the frames, and especially the hardware, are terrible. We used their triple pane casements on a recent project, and most of the windows do not close properly, and hardware is literally snapping off in our hands! This after months of trying to get their sales people to resolve issues with poor functionality.

    1. Jonny_H | | #7

      Which series did you use -- 325 series outswing casement or 700 series inswing casement? I'm literally like a day away from dropping an order for a house worth of windows -- mixture of 300 series tilt-turn and 325 series casement, and some fixed, and you've got me worried now!

      1. Forrest Twombly | | #8

        We used the 325 series. I think part of the issue is that some of our sash sizes are quite large and with triple pane windows they are heavy! The hardware just isn’t up to the job. But even the average sized Casements seem to be having trouble.

    2. Expert Member
      Akos | | #9

      Triple pane windows are very heavy, it could be the sales rep was looking at the double pane size limits. Casement hardware puts a lot of stress on the window frame, even ones that are bellow the limit can cause issues.

      For any triple pane window in North American frames, I would stick to fixed, awning or sliders.

      Tilt and turn frames and hardware are significantly sturdier and you can go much larger glass without issues. I have a 30"x96" triple pane tilt and slide at home and never had issues.

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