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Windows for Passive Solar (continued): Serious, Thermotech, etc.

user-869687 | Posted in Green Products and Materials on

I am selecting windows for a house in Portland, OR, a marine climate. The heating demand is not extreme but it is a heating climate, and this is a passive solar design. There are no plans to include A/C. As has been discussed a few times on this website, it’s hard to find a domestic manufacturer of windows with a good U-value and high SHGC. The recommendation from Martin Holladay is to choose Canadian windows, e.g. Thermotech, Inline, Accurate Dorwin. A few people have chosen to import windows from Germany, at higher cost.

It would be ideal to source windows from a company nearer than southeastern Canada (or Europe). Serious Windows is on the west coast, but my instinct is to avoid suspended film glazing. The warranty has a lot of exclusions and doesn’t specifically state that the film is guaranteed not to cloud or yellow. By comparison, the warranty for Pella does specify that their glazing will not cloud for 20 years. Of course they don’t seem to offer a high SHGC option.

It seems the manufacturers need to be badgered into offering different glazing up north. Any ideas about this?

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  1. Riversong | | #1

    Actually, and probably because of badgering from people like me, Pella now offers "Natural Sun" double glazing with a SHGC of about 0.50. This is available in both the wood/aluminum-clad Proline and fiberglass Impervia lines.

  2. Dan Kolbert | | #2

    Thomas - why are you avoiding Canadian windows? The distance? And Robert - you've talked about this Pella product several times, but I can't find any reference to it anywhere else. You got more info?

  3. Garth Sproule | | #3

    Accurate Dorwin is located in Winnipeg MB if that helps...

  4. user-869687 | | #4

    Cascadia is in Canada but at least it's B.C, certainly closer than the others. However, none of the windows listed on their ratings page are anywhere close to the desired numbers. The highest SHGC is 0.32. I've just alerted the rep about this problem. Badgering is underway.

  5. user-869687 | | #5

    I should add that RR's suggestion about Pella Impervia is a good one and they are the current front runner. I didn't find performance numbers on their website though. It seems to be designed to avoid overwhelming homeowners with technical details.

  6. user-869687 | | #6

    On a related note, if window companies really want to serve the green building community, they should have standard widths that fit into advanced framing dimensions. I've cleverly laid out windows with rough openings of 22.5", 3'-9" and 5'-9" based on the framing, and these are not standard sizes. Of course a lot of window manufacturers don't even have standard sizes.

  7. Riversong | | #7


    I can't say if Pella offers this glazing in other parts of the country, but I believe that everything comes out of their Iowa plant the same.

    Design specs are to be found at the Pella Architectural Design Manual:

  8. mike eliason | | #8

    cardinal makes a loE triple pane (179#2/clear/179#5) w/ 69%VT, 0.57SHGC and U=0.14 if argon-filled.

    had nominal success in getting mfr's to at least look at using this instead of the 0.30/0.30 crap.

    not hideously tinted like serious, either.

  9. user-869687 | | #9

    The Cascadia rep tells me they offer Cardinal 179 on triple glazed units for high SHGC. That's good. Meanwhile their energy charts seem to assume you want Cardinal 366 (low SHGC). It's good we're having this discussion, because specifiers may not be aware of what some manufacturers have available. It would be kind of amazing if any Canadian window company did not offer glazing suited to northern climates.

  10. Jesse Thompson | | #10

    Cascadia and InLine are parallel companies from what InLine has told me. InLine will install Pilkington / LOF Energy Advantage glazing as well as Cardinal 179, but the LOF EA has a bit better SHGC than the Cardinal 179. I would assume Cascadia would do the same, but you'll have to ask them directly.

  11. Jesse Thompson | | #11

    You can check specific NFRC calculations for individual manufacturers at this link:

    InLine shows many more glazing options than Cascadia, but they both show Cardinal 179.

  12. user-869687 | | #12

    Jesse, I did notice that Cascadia seemed to borrow a lot from Inline, or else the other way around.

    Other observations: Pella offers foam fill on their frames, apparently as an option, It makes a small improvement in the U-value. Pella's warranty is 20 years on their glazing units. Cascadia offers 10 years. Cascadia frames are hollow, not insulated.

    I've run some simulations with RESFEN. There is very little difference between double and triple glazing. The higher visible light transmittance of double glass is an important plus for Portland's gloomy winters. I think the improved U-value of triple units would matter more if there were more glazing area, or more HDDs (that is, not as mild of a climate).

  13. Jesse Thompson | | #13

    Thomas, my impression is that the product is exactly the same, but that Cascadia might exist so InLine doesn't have to ship glazing units over the Rockies.

    The main reason to have triple glazing in your climate is for comfort without having to pay for heat distribution underneath your windows in winter. Double glazing will be cold enough that convective loops can form, with cold air dropping down the face of glass. Triple glazing would warm up the inside face of your glazing and you can maintain a comfortable exterior surface temperature even without a heat source at the perimeter of your building.

  14. Riversong | | #14

    Portland OR has only 4400 HDD climate. A good double-glazed, lowE, argon window will be comfortable at any outdoor weather condition. There will be no convective loops and no perimeter heat source will be necessary.

    Even in my 8500 HDD climate, double-glazed windows are very comfortable and may be more efficient than triple-glazing when factoring in passive solar gains.

    The financial payback for the upgrade to triple-glazing can be decades.

  15. mike eliason | | #15

    an uber-libertarian friend in portland wanted me to run numbers on replacing his single pane windows. 1000 sf glazing, mostly southern, well shaded in summer, baseboard heating
    per PHPP, the loE179 performed about 45% better than the double pane low-e wood clad window he was looking at using, and payback was less than 8 years, less if cost of electricity goes up (best reason in my book)

    sound attenuation was also another selling point.

  16. Riversong | | #16


    I don't know how your friend's politics effects the relative efficiency of his window choices, but it appears you're trying to make a point by comparing the best triple-glazing available to an unknown and almost certainly poorly-performing double-glazed alternative. And your comparison doesn't indicate whether the frames on the two options were the same or you compared a much better performing frame system.

    Sounds like you're trying to brag about the gasoline efficiency of a Prius by comparing it to a Hummer.

  17. user-869687 | | #17

    Triple pane windows have a few downsides. First, as mentioned, they have lower visible light transmittance. This may not matter when the sun shines brightly, but it could be a bummer when the skies are gray. That unfortunately is a common state of things around here. Second, they weigh more, which puts more strain on any operable leaf. And third, they cost more, because they use more resources. The reality is that windows in a detached house can be open for most of the year in this climate. Whenever there are windows open, the U-value matters not.

    I think if there were going to be triple pane windows, there should be a larger glazed area to compensate for reduced visible light. That would add quite a bit to the window budget, to have both a more elaborate glazing type and more of it.

  18. Riversong | | #18

    Just on the basis of energy savings payback, I compared a half dozen window options for a small, somewhat passive solar lake house I designed for a client in southern VT, including Thermotech, Serious and Accurate Dorwin. None of the alternatives to Pella Impervia Natural Sun (high SHGC) offered better solar gain and the payback periods were from 30 to 70 years, because the Pella pricing was unbeatable for a quality window (the others cost between 38% and 84% more).

  19. user-869687 | | #19

    I am tempted to say that it's not particularly "green" to choose to live in an area with many thousands of heating degree days. In my own humble abode, I currently use 2/3 of the maximum total energy use allowed within the Passive House standard. That is possible largely due to a tolerant attitude about thermal comfort. The HDD count drops as the accepted indoor temp drops, because that reduces the delta-T. Any house becomes a Passive House when you decide not to bother heating it. However, it might be dangerous to try that in North Dakota.

  20. Riversong | | #20

    it's not particularly "green" to choose to live in an area with many thousands of heating degree days.

    I guess the Eskimos and the Inuit don't live as green as you do, then?

  21. user-869687 | | #21

    Ah, brilliant observation. The remarkable thing about a house made of snow is that it does such a good job maintaining 32 F degrees, even when the outdoor temp is much colder. This makes perfect sense, so long as people are happy "setting the thermostat" at 32 F. It's quite warm, at least compared to minus 60 F.

    On the other hand, a milder climate (4400 HDD) allows survival even for people less hardy than the native Alaskans. The worst case scenario is when people choose to live somewhere very cold and still expect 68 F indoors. For them, triple glazing may be required.

  22. Riversong | | #22

    It's a myth that a snow shelter maintains 32°F. That's the freezing point of water and has no relation to the delta T of any kind of shelter. If the interior stayed at 32°, it would be constantly melting.

    Snow is a moderately good insulator, about R-1/inch, so the interior temperature - as in any insulated structure - depends on the outside air temperature and the rate of interior heat production.

    I've slept in a number of snow shelters. In one quinzee, with two human bodies sleeping inside and outside temperature at -15°F with high winds, the interior temperature was 20°F - a pretty impressive 35° delta T.

    But the secret of winter comfort of the northern peoples is to wear their shelter on their bodies and rely on the igloo or skin tent to keep out the worst of the weather. They also eat a very high fat diet with no fruits, vegetables, or starches.

    The National Outdoor Leadership School recommends a 30% fat diet for winter activities to keep the furnace stoked for slow burn..

  23. Robert Clarke | | #23

    Our company, Serious Materials, and predecessor Alpen, have manufactured architectural glass and windows based on Suspended Coated Film (SCF) for 29 years. Early threats to film yellowing, or degradation of any kind, were clearly resolved during the late 1980s and early 1990s through the transition to UV blocking materials and "dual seal" insulating glass technology. Countless Serious Materials projects with two decade plus histories go forward with crystal clarity and super insulating performance.

  24. Riversong | | #24

    degradation of any kind

    Robert Clarke,

    Are you suggesting that a plastic film does not degrade over time or lose its optical properties, or that plastic has the longevity of glass?

    I will grant that the reduced weight is a significant advantage of suspended film glazing. But I'm doubtful about durability and longevity.

  25. user941025 | | #25

    [problem in my original post here finally resolved -- deleted.]

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