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Triple-pane windows

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

Asked by John Barbuto
Posted Jan 9, 2013 12:38 PM ET
Edited Jan 9, 2013 5:55 PM ET


5 Answers

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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

Answered by Martin Holladay
Posted Jan 9, 2013 2:06 PM ET
Edited Jan 9, 2013 2:09 PM ET.


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

Answered by Jin Kazama
Posted Jan 9, 2013 6:49 PM ET


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.

Answered by Dan Kolbert
Posted Jan 9, 2013 11:01 PM ET


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.

Answered by Martin Holladay
Posted Jan 10, 2013 6:06 AM ET


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.

Answered by Martin Holladay
Posted Jan 10, 2013 6:08 AM ET

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