GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Audio Play Icon Headphones Icon Plus Icon Minus Icon Check Icon Print Icon Picture icon Single Arrow Icon Double Arrow Icon Hamburger Icon TV Icon Close Icon Sorted Hamburger/Search Icon

Community and Q&A

European windows vs. North American windows

Steve Young | Posted in Energy Efficiency and Durability on

I have read many blogs and Q&A pages from this web site and I am still somewhat confused about European windows.

First of all, there is the U-window differances because of the differing testing conditions (Europe uses a 0 to 20 degree delta T, while NA uses a -18 to 20 — All degrees C). So should I pretty much ignore the U valuse, if I am looking at the “best” glass and frames? and complare the SHG and VT only? The Optiwin figures (SHG 0.52) seem to beat anything that Thermotech has (SHG 0.42), or is that somehow measured differently in Europe too? Transmittance has to be measured the same?

There is also the installation method. Most NA windows have a nailing flange while European windows seem to be flangeless. There are advantages to both, though. But isn’t it ideal to place the window somewhere midway into the depth of the wall? Don’t you give up insulation value by placing the window out by the siding? Of course, having the window install out that far makes for a much easier finishing process with respect to water plane detailing. European windows, if set into the wall, would require more thought, but you also get to wrap a little foam up to the frame (I suppose this could be done inside and outside), which seems like a good idea, albeit somewhat time sonsuming.
Do I have this right? Are there other considerations?

As for costs, I have seen figures all over the place on this web site. That might have to do with the various dates over which the numbers were posted. Can folks that are using the latest amd greatest window technologies post current relative quotes that they have received for their projects?

I like the idea of Figerglass windows. I hate PVC and wood is OK, if that is what I have to go to to get a superior frame. I cannot find any European Fiberglass window makers. Is there a reason for this?

FYI I am looking into a Passive House build for retirement, probably in zone 5

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    European U-factors should not be ignored. Lower is still better than higher. However, you are correct that they cannot be directly compared to the U-factors published in North America.

    You have a good understanding of the installation issues, and the current debate between those who like outies and those who like in-betweenies.

    If you haven't read this article yet, you should check it out: Passivhaus Windows .

  2. Mike Eliason | | #2


    as far as i've been able to tell, the EU glass mfrs have been pushed by both policy and demand for high shgc glazing w/ ultra low u-values. there are some spectacular glazing units from glastroesch and guardian. guardian has plants in NA, but they don't roll off the high performance glass because there is no demand. there are slight differences in how they calculate, but the numbers don't appear to be off by a significant factor - even given the lower deltaT in EU.

    as for EU fiberglass windows - pazen's enersign is the only one i know of that's PH rated. it also has a stunningly minimal profile.

    and as for windows in zone 5... placing windows in the middle and overinsulating the frames is better, performance-wise, however depending on solar access/insolation - may not be necessary. we'd love to use NA windows and glass mfr'd in NA for the PHs we're working on - but no one seems willing to step up to the plate and produce what we can get from EU for cost, performance, quality.

  3. Shane Claflin | | #3

    Is there a way to convert EU u-values to NA?

  4. Greg Smith | | #4


    The current advantage that Euro windows appear to have over NA windows (exempting the differences is how performance is calculated) is in sash and frame design and application rather than glass package.

    As Mike pointed out, there are some spectacular glazing packages available in Europe, but the same technology is available on this side of the pond as well. The best European glass pacakages aren't any better, or worse, than the best NA glass Mike also pointed out, it's comes down to getting NA window companies interested in offering those packages to people who want them.

    For example, you (well, window company) can get a Cardinal glass package right now with VT .70, SHGC .58, U-value .15 with argon fill. Change it to krypton and the U-value is going to be in the .13 range without changing the other factors. Add their surface 6 coating and U value drops to .12 with argon (about .10 with krypton), but SHG and VT will "suffer" - going to .53 and 68% respectively.

    Within the window industry, it's something of a given (depending on source of course) that translated Euro U values are at least 10% "better" than the equivalent NFRC rating. Some folks will suggest the "advantage" is closer to 20% when you start getting down into the low teens and better.

    I have seen a particular (converted from Euro specs) U.14 German window that came in at close to U.17 using NFRC criteria...but again it was just one example and like most things that you read on line the occasional grain-of-salt is always in play. And that is still a truly amazing number in any case.

    A number of the large American companies are starting to enter the "better than pretty good" market in large part because of the current economy.

    Superior performance (close to PH-type standards) windows are still a fringe market on this side of the world, but its a fringe market that is growing and it represents a potential market share in a time when increasing market share is not very easy to do. The big guys may have taken awhile to find this market, but they see it now and are reacting to it - some a bit slower and some a bit faster - some more aggressively and some less aggressively - but they are all at least aware of it.

    People who visit this board who are familiar with the really high performance windows have at least a passing acquaintance with the "big 5" Canadian fiberglass companies. I can think of a couple other companies in Canada who match the energy performance numbers of the windows produced by those companies, but do it in vinyl and not fiberglass. But, if I recall correctly, only one of those seven companies is even in the top 100 largest window companies in North America (and I could be wrong about that since I am doing it by memory...but I think I am correct).

    Again, it is still a fringe market, but one that is growing.



  5. GBA Editor
    Martin Holladay | | #5

    Oberon / Greg,
    It's great to have your expertise shared here.

    GBA readers: Oberon knows what he's talking about. He's a valuable information resource.

  6. Mike Eliason | | #6


    in our research, the glass in NA isn't quite up to par with what's being produced in the EU - even if you take a 10% difference based on the alternative means of calculating u-values..

    the u-value of the cardinal glass isn't really adequate for most projects we're working on for PH, and the SHGC could be higher as well. even more so for climates colder than seattle.

    a few glazing specs we're working with (EU values):
    glastroesch silverstar TRIII E (AR) SHGC - 64, U-value 0,6 W/m2k or 0,105 BTU/hr.ft2.F
    glastroesch silverstar TRIII E (AR) SHGC - 62, U-value 0,7 W/m2k or 0,123 BTU/hr.ft2.F
    glastroesch silverstar TRIII E (AR) SHGC - 66, U-value 0,8 W/m2k or 0,14 BTU/hr.ft2.F
    guardian climaguard nrg (AR) SHGC - 62, U-value 0,64 W/m2k or 0,11 BTU/hr.ft2.F
    guardian climaguard premium (AR) SHGC - 49, U-value 0,64 W/m2k or 0,11 BTU/hr.ft2.F

    all those glasses have a VT north of 70 as well. additionally, the incorporation of krypton can drop the u-value to below 0,09 BTU/hr.ft2.F while maintaining an SHGC north of 60. for us, it's the combo of higher SHGC and lower U-value that make a fairly significant difference (e.g. our specific heating demand w/ the 2 guardian glazing units v. cardinal goes from 4.35kBTU/ft2a to 5.76kBTU/ft2a - dropping us out of PH contention without adding additional insulation).

    i'd love to see a better definitive analysis on the U-values. you'd think after 5 years, that's something that a head organisation would have undertaken already... even the south koreans have a certified frame at this point!

  7. Jesse Thompson | | #7

    Great details everyone, it never smelled right to me either that Euro glass manufacturers had some secret sauce that US manufacturers didn't. Especially when they seem to all be multi-national corporations selling products across the globe. It seems to all come down to good old fashioned sales demand, regulation and market movement.

    Guardian is a great example. Mike posted the following glass packages from them (with capitals and periods added just to smite him):

    Guardian Climaguard NRG (AR) SHGC - 62% or 0.11 BTU/hr.ft2.F
    Guardian Climaguard Premium (AR) SHGC 49% or 0.11 BTU/hr.ft2.F

    Add 10% to account for different US NFRC vs euro ISO thermal measurements:

    Guardian Climaguard NRG (AR) SHGC 62% and 0.12 U-value BTU/hr.ft2.F
    Guardian Climaguard Premium (AR) SHGC 49% and 0.12 U-value BTU/hr.ft2.F

    From Guardian in the US, here is the best cold climate triple glazed option:

    Guardian Climaguard 80/70 + 80/70 (Low-E #2 & 5): SHGC 58% and 0.14 U-value BTU/hr.ft2.F
    Guardian Climaguard 80/70 + 71/38 (Low-E #2 & 5): SHGC 45% and 0.13 U-value BTU/hr.ft2.F

    And we've never been able to get Guardian 80/70 from our local window company that uses their glass, they use the 71/38 instead which is 35% SHGC, 0.16 U-value.

  8. Mike Eliason | | #8

    ah, but there is a secret sauce of sorts... the EN calculation apparently favors thicker spacing between panes, where as the NFRC calcs favor thinner ones...

    well, and the EU glazing mfr's have apparently figured out how to do the ultra-low iron glass without costing an arm and a leg. we had it priced out on 2 NA mfrs and the increase in price was phenomenal. with the EU passive house windows we imported, there was no cost increase for the ultra high SHGC glass. in actuality, it was a cost decrease - as the windows were less expensive than the NA window we would have otherwise used, and then because of the high SHGC, we were able to shed a few inches of insulation as well.

    surely there's got to be a non-democratic U.S. passive house organisation that would have felt it necessary to provide some leadership on this issue in, say, the last 5 years... considering the windows are the weak point of PHs here, one would expect the confusion to have been resolved.

  9. Jesse Thompson | | #9

    The kicker is that the European delta T of 32°F - 68°F makes a ton more sense to use as a standard for insulating value than the 0°F - 70°F for NFRC. How many hours does your average US window sit at 0 degrees?

    For our projects, even up here in cold Maine, we would certainly rather have a wide air space that is optimized for 32°F than 0°F.

  10. Greg Duncan | | #10

    Unless I'm looking at the U Values backwards, the bottom line appears to be that we can safely use NFRC numbers in PHPP.

  11. GBA Editor
    Martin Holladay | | #11

    Oberon / Greg,
    Your wording is a little obscure.

    When you write, for example, that "11.5mm airspace advantage CEN by 8%," I assume you mean something like this: "If the same IGU with a 11.5 mm air space is measured by both the CEN standard and the NFRC standard, then the CEN standard results in a U-factor that is 8% lower than the NFRC U-factor."

    Is that what you mean? Or is it the other way around?

  12. Keith Gustafson | | #12

    The obvious answer is for euro manufacturers to submit their windows for evaluation by NFRC

    this link:

    shows a series of graphs about this subject, they have been linked here previously

  13. Greg Smith | | #13


    I wrote my reply while eating lunch, and posted without a reread, so I am going to go back now and see if I need to do a little editing.

    But to answer your question, the wider the airspace the more it benefits CEN U-values.

    Stating 8% "advantage", I meant exactly what you said, that the CEN U values were 8% lower (better) than the NFRC even though the glass packages were absolutely identical.

  14. Greg Smith | | #14

    Following up once again after a bit more research, and since this isn't an area I deal with alot in my day job (comparing EURO and NA values), I made a couple of inquiries with the right person and here is a bit more of an explanation as well as a few numbers to use for comparison.

    Keeping in mind that the following info is for glass packages only and not for whole window values.

    Everything else being equal (meaning glass package), Euro window sash and frames are often built to a different standard of energy performance vs most NA windows - that's a given and there is no argument.

    In discussing glass packages and U values, Euro calculation versus NFRC calculation does result in an advantage for the European product in many cases. Not withstanding using different glass type, thickness, etc., which are design differences, and not calculation differences, and can result in an advantage in determining various performance characteristics as noted previously.

    As everyone reading this probably already knows, European calculations. or CEN (Wiss), use a different Delta T to calculate U value versus NA or NFRC. Specifically, winter condition U value is calculated with a range of 32°F - 68°F for the European standard and 0°F - 70°F for NFRC. So what's it mean?

    About 60% of heat loss through a dual pane clear glass window is radiant and about 40% (give or take a percent or few) is conduction. If you want to cut down on radiant loss you add a LowE coating and it doesn't matter if it's high solar heat gain coating or low solar heat gain coating since both versions will block radiant heat loss in the dead of winter... low solar heat gain coatings are actually a little bit better at it than are high solar heat gain coatings.

    So you use a LowE coating and you block a good bit of the radiant heat from leaving your home. Now what about that conduction part? Well to start with, using a Lowe coating actually INCREASES conductive loss thru the window. So how do you deal with conduction loss thru the glass portion of the dual (or triple) pane window?

    To do that you need to do something about the convection current that exists in the airspace(s) of the IG unit because its that convection current that is dragging the heat from the warmer inner lite and handing it off to the colder outer lite so that it can be conducted thru the glass into the cold air outside. The warmer the interior lite and the colder the exterior lite, then the more convection inside the IG space and the more heat loss due to conduction. Simple physics.

    So in order to "prevent" convection currents inside the IG space man invented argon. Argon is lazy. Argon slows convection currents. Man saw this was good, but not good enough, so man invented krypton. Man saw krypton was very good, but also very expensive, so maybe argon is better when doing cost versus benefit analysis.

    But beyond that, some man (or perhaps woman) wanted even better control of the airspace and soon invented xenon - which is better than argon or krypton at slowing convection currents, but it is also insanely expensive.

    And, for everyone who remembers high school chemistry, argon, krypton, xenon are three of the six noble gasses - they are "ranked" 3, 4, 5 on the list of noble gasses (helium and neon are 1 and 2). Number 6 on the list is radon, but I suspect no one is going to use radon as an inert gas in their IG units without a really innovative marketing program. But, I digress and I have gone way off topic - sorry.

    So back to topic. Window restoration folks will often cite the width of the airspace between the inner window and outer storm window as an inherent energy advantage of single pane glass with a storm window over a modern IGU because greater width equals better insulating capabilty.

    And if it wasn't for the laws of physics and those troublesome convection currents they would be right, wider would be better. But in the real world convection currents increase as the gap between the two lites of glass increases. This is a bad thing and once again the reason for inventing argon, krypton, and xenon (not so much radon).

    And as we all know, the major factor resulting and affecting the convection current inside an IG airspace is Delta T between the inner and outer lites.

    Euro calculations are based on a lower Delta T and NFRC on a greater Delta T - this difference means that Euro calculations allow wider airspaces - and as mentioned previously, wider is better if you aren't worried about those pesky convection currents. Ergo, score one for Euro calculations if you are wanting lower calculated U values.

    In my previous post I mentioned ~10% advantage for Euro calcs versus NFRC, going on to about 20% as the U value gets lower. Not exactly definitive, so here are some real numbers but with a disclaimer since these are for dual pane glass packages and not triple. I currently don't have triple pane numbers available.

    For this illustration the dual pane soda-lime float glass, surface 2 has moderate (2 layer silver) LowE coating, 3.0mm glass, argon fill:

    8mm airspace results in lower NFRC U values by about 4% versus CEN
    10mm airspace is a dead heat, no advantage to either
    11.5mm airspace results in lower CEN calculated U values by 8% versus NFRC
    13mm airspace favors CEN by 15%
    16mm airspace favors CEN by 25%
    19.5mm airspace favors CEN by 26%

    As mentioned earlier, I didn't run the calculations, they were sent to me from a friend who does a lot of work in this area (I say that not to hide from the results, but so that I am not taking credit for someone elses work - I have no doubt about the accuracy),

    Finally, and to reemphasize, these numbers are based on simple dual pane IG units and are not intended to suggest overall window performance.



  15. Bronwyn Barry | | #15

    Hi Steve et al,

    Yes, there really is no good reason that we are not building 'super-windows' right here in the US (other than there has previously not been a huge demand for them.) To help change that situation, the American Passive House Network and the Passive House Institute are hosting a workshop on how to build and certify locally made Passive House windows. Details on the workshop can be found here: (The workshop is already 1/5 full, so the interest is clearly there.)

    For those not interested in building or certifying locally made products, I've found that a delicate balance between frame, glazing spacer bars, SHGC and the actual installation of the window within the wall is required. (And this 'formula' applies to all windows, not especially Passive House ones.)

    Frame thickness and insulation levels depend on your climate. I’m now a fan of all-wood frames as wood is the most sustainable material and has the most affordable longevity when given a small amount of maintenance. (Has anyone seen 100+yr aluminum-clad windows?) ‘Nuff said on frames.

    Spacers should always be of the 'super' variety and no IGU manufacturer should be installing aluminum or even stainless spacers if they want to play in the high performance sand-box. The width of this spacer should also be much thicker than we have typically been using.

    Historically the spacer width has been determined by a graph showing the diminishing returns between the convective heat losses and conductive heat losses within the air/argon space between the glass panes. (This is what Oberon was referring to as the 'glass thickness', rather than the thickness of the glass panes themselves.) The graph was plotted based on outputs using the NFRC external boundary temperature and surface film co-efficients determined by that protocol. As others have mentioned, that protocol has a 39degC delta T, which works well in northern MN and AK. The graph also only plotted for 2-pane, and not 3-pane IGU’s. We should actually use wider spacers in most of our climate zones, as our delta T conditions aren't as severe in most of the rest of the US where the majority of windows are installed. Apparently the different surface film coefficients used in the NFRC protocol vs the ISO 10077 variation used for Passive House certification also make a difference. (I attempted a graphic comparison of the two protocols here: The conclusion is deceptive on this study, so don’t assume the results are ‘almost the same.’)

    Then there's the SHGC. This one is a load of fun. I’ve spent days fiddling with multiple combinations of glass for each orientation only to end up with windows installed in all the wrong places when they reached the jobsite. (A common story I’ve heard from others too.) I've reluctantly agreed to keep trying this, but only because I now work with a builder and will be on site when the windows are installed. Here's what I'm calculating - and I'm still open to changing my mind here - if I spec the windows as all high SHGC, this provides the maximum amount of free heat and the lowest Heat Demand number possible. However, the result of that choice is to bump up my cooling load. But, if I then use passive shading options to control summer heat gain, I get the best of both worlds: maximum free heat and minimum cooling load. The foundation of this idea is to allow the glass and the windows to do what they do best: provide the most light and the most free heat (in winter.) You do then need to employ alternate materials and methods to mitigate summer heat gain. These can be deciduous trees, trellises and horizontal and vertical shading fins. You can also use active/motorized shades, or the old-fashioned operable shutters.

    I'm still working on the cost-benefit analysis of that above equation. Using glass to control your heat gain on the east and west may well be the cheaper option. It will also be the only option in buildings over 4 stories where wind loads become a factor for exterior shades and fancy glass will be a much more viable option. The combination will vary by project, but the essential concept is Miesian: use each product (or material) for what it does best: glass is for light and free heat; overhangs and other materials are best for shading.

    Lastly to the install: if we're going to remain tethered to the nailing flange, we leave one of the best opportunities for improving window performance numbers - and reduced interior condensation risks - on the drawing board. I do get that this is hard for builders. Who wants to add a more complicated flashing (read: risky) and installation process (read: costly) to their already complicated high performance building project? However, if you are already building high performance walls with exterior insulation, you've automatically signed up for a slightly more complicated window install. There is typically no wood to nail the flange to on the outside of your wall anyway.

    As has been previously mentioned, the optimum installation typically falls somewhere in the middle of the wall insulation layer. You have to remove the nailing flange to install a window here and the sill is the trickiest part to deal with. Here is where Euro windows have the edge: they typically build a completely different profile for the base of the window than the jamb and header. This is to accommodate a drainage sill pan that attaches to the base of the window and includes a positive drip edge. I’ve seen some good install details that have figured out a ‘work-around’ that accommodates the North American all-one-profile frame. (See the Cascadia install detail at the sill.) However, I’m hoping that US window manufacturers will modify their sill profiles to make the install easier for contractors and the flashing a bit more bullet-proof at the sills.

    Thank you for indulging me by reading to the end of such a long post. This is one of my favorite topics and I’d love to receive feedback, particularly on the All High SHGC idea. I promise to stick to pithy one-liners for the rest of the month.

    Best regards,

  16. GBA Editor
    Martin Holladay | | #16

    Back in the 1980s, we old-timers learned a trick to use when designing passive-solar homes with orientation-specific glazing: when designing the house, make sure that the size of the south-facing windows is different from the size of the west-facing windows.

    If the rough openings are different, the window installers can't screw up by putting the wrong window in the wrong opening.

    Of course, your window supplier can still screw up and deliver the wrong glazing... but that's another story.

  17. GBA Editor
    Martin Holladay | | #17

    Oberon / Greg,
    Thanks for verifying that I was correctly interpreting your use of the term "advantage."

    (To confused readers: since Oberon is talking about two test methods being applied to the same IGU, there is no performance advantage -- just a different number reported in the specs.)

  18. Bronwyn Barry | | #18

    Thanks Martin - That would solve the problem for new builds but what did you old timers do on retrofits with existing opening sizes?

  19. GBA Editor
    Martin Holladay | | #19

    In my case, I did the work myself. Nothing beats the Vermont jack-of-all-trades approach -- one in which the design/build contractor runs the wiring, does the plumbing, and hangs the drywall.

    But from what I've read, that's not how they build houses in California anymore.

  20. Steve Young | | #20

    Are windows actually tested in a chamber or is it all done by computer modeling? If it is the latter, couldn't the input parameters simply be changed to determine U's for NA and Europe. I think that I read how the folks at Thermotech tried modeling European windows and couldn't duplicate their performance numbers. (PHIUS forums, I believe)
    Where is PHIUS in all this? Shouldn't they be pushing for some sort of standardization or conversion factors? How does the Planning Package deal with the incompatible testing methods?
    So, if I understand this correctly, European glass has two things (special sauce, perhaps) that differentiate their products. One, they use a very clear low iron glass that allows better SHG. Two, they use a wider spacer that works to their advantage in Europe, but doesn't work (test well) in colder climates (like Canada and northern USA). Does that mean that we are talking apples and oranges, in that we cannot, and should not, compare the two products? Just like we choose windows for specific orientation, are European windows customized for that climate only?

    On a personal note, I am very impressed with the caliber of discussion on this topic.

  21. GBA Editor
    Martin Holladay | | #21

    "I am very impressed with the caliber of discussion on this topic." I agree -- some of the smartest glazing people in the country are contributing to this discussion. Thanks to all who are participating!

  22. Mike Eliason | | #22


    'Where is PHIUS in all this?'

    good question. it's one of the more annoying gaps that's not been resolved. since PHIUS basically forced PHI to kick them off the bus, it seems that PHIUS is going its own route on windows. there is an upcoming session at the conference on their new 'window value verification and endorsement program' but i've not heard anything about it as of yet. the 'endorsement' bit sounds a bit problematic.

  23. Bronwyn Barry | | #23

    Martin - yes, I'm now working at a design|build company (in California btw) and that is why I'm still willing to try the orientation-specific glazing approach.

    Steve - Passive House windows are not tested in a chamber so I'm working directly with the Passive House Institute to do exactly what you suggested: have local simulators change their boundary condition assumptions etc. and generate the alternate outputs. So simple it should have been done years ago! Details here: .

    Now I'm way over my one-liner quota... oh well.

  24. Greg Smith | | #24


    "Thank you for indulging me by reading to the end of such a long post. This is one of my favorite topics and I’d love to receive feedback, particularly on the All High SHGC idea. I promise to stick to pithy one-liners for the rest of the month."

    No need to thank anyone, that was a great post.


    "(To confused readers: since Oberon is talking about two test methods being applied to the same IGU, there is no performance advantage -- just a different number reported in the specs.)"

    Thanks for that clarification. I had the same thought but you worded the explanation much better than I would have done.


    Low iron glass is readily available in NA. It comes down to supply and demand - the demand for low iron in NA is simply not there for residential windows.

    You will find it in solar panels, furniture, commercial wall systems, decorative glass products....and so on.

    Again, its just a matter of getting the NA window folks to see a demand (market share) by offering it.

  25. Bronwyn Barry | | #25


    Incidentally the low iron glass with higher SHGC options that the Euro's now sell were not available there either until fairly recently. The Passive House movement pushed the market in that direction and suppliers eventually responded. The really high (0.6 to 0.72) - and I'm talking for triple pane here - IGU's are still not easy to come by and do cost more. When I was representing a range of Euro windows a couple of years ago, I was told that production runs for super high SHGC glass were still small compared with the more typical glass. Prices were also higher and lead-times were longer. Funny how the market works the same there as it does here!

    Can you name your source of low iron glass please? I would love to help boost the demand for it here.

    Many thanks.

  26. Greg Smith | | #26

    Good morning Bronwyn,

    No problem.

    AGC produces low iron glass called "Krystal Klear". At 3mm it has a VT of 93.3% and two layers is 86.7%.

    VT measurements for all products listed were taken using a BYK-Gardner THC (yeah I know) measurement meter. THC, in this case, stands for Transmission, Haze, Clarity.

    Cardinal produces mid-iron and low-iron glass and while I don't have a mid-iron sample I do have several low-iron ones....

    However, as I look thru the papers I brought home, I realize that I apparently forgot the paper that had the VT measurements on it - except for Krystal Klear which was on a different sheet. So, I will list the products but without any measurements.

    All the products listed have VT's in the 92-93% range. None of the products really stands out from the rest in that area.

    Once again, Cardinal produces mid-iron and low-iron product. As I recall VT was about 92% for mid and 93% for low iron. Cardinal produces low iron at 2mm (among others), I don't believe anyone else produces that thickness. Cardinal calls their low iron, Cardinal Low Iron. Not real imaginative.

    Guardian produces Ultrawhite on this side of the pond. They have a couple other low-iron products that they produce in other parts of the world

    PPG - Starphire. This is a very nice product. Very clear. It comes in 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm.

    Pilkington Optiwhite. Pilkington has been fabricating this product in Europe for many years, but they started producing it in North America in 2010 or 2011 as I recall. Pilkington also produces a less expensive product that they simply call low iron. It's comparable to Cardinal's mid-iron in my opinion.

    Other than Guardian, I have samples of all the products that I mentioned.

    When viewing the different products from the edge, an experienced observer can tell them apart Pilkington, for example, adds cobalt to their low iron which gives it a very slight blue tint. Very nice looking color and it doesn't appreciably affect the performance.

    Starphire is very clear. The edge view is nearly as clear as the face view. AGC and Cardinal have a very slight (VERY slight) "yellowish" tint from the edge.

    In all cases, the only way to "see" the very slight edge differences is to view different versions next to one another. Viewed indenpendently, they all look absolutely clear. For comparison, ordinary float is distinctly green when viewed from the edge (preaching to the choir).



  27. Bronwyn Barry | | #27


    Wow! This is a goldmine of glass info. Many thanks. I hear that the 2mm glass Cardinal is producing will be coming out in the next generation of Euro Passive House windows. I'm looking forward to seeing it. Windows will be changing radically in the next decade. Not sure if you have seen the work of two very smart Polish window designers who are using thin-film glass in their prototype designs here:

    I'll be sure to share your glass info with local manufacturers attending this upcoming workshop: If you are in San Francisco any time soon, please contact me at passivehousebb'at' I'd love to connect directly.

    Best regards,

  28. Greg Smith | | #28


    I have heard about the Cardinal 2mm going into European triple panes. I have also heard that Cardinal is the only glass company that has certified 2.0mm to European CE specs, but I haven't tried to verify that.

    You are welcome on the glass information. I'm glad that it may be of some benefit.



  29. Greg Smith | | #29

    Thanks Martin, I truly apreciate the kind words.


    If we do an apples to apples comparison, then glass packages are going to be pretty much identical whether the glass package is NA or Euro.

    One of the differences in many high-end European glass packages (re. your examples), is that in Europe it is much more common to use low-iron glass in high end (often spelled PassivHaus) windows rather than "conventional" float glass. In NA, it is still uncommon to use low iron glass in window glass packages.

    The use of low iron glass is what gives the Euro glass packages the high solar heat gain advantage illustrated in your examples.

    Additionally, Euro windows are more likely to be fabricated with a thicker glass package (heavier glass with wider airspace) than are NA window makers - again a slight performance advantage as shown in your examples.

    The lower Delta T used for Euro calcs versus the greater Delta T used for NA U value calculations is an advantage for Euro designers resulting in the apparent U value advantage of the Euro glass package / window. The Delta T difference allows for the use of wider airspace in Euro IGU and window performance calculations.

    So given all that, I agree 100% that Euro glass packages often have superior glass package energy performance numbers, but again this is based both on how the performance is calculated as well as differences in fabrication philosphy rather than any technology advantage.

    I agree that it seems like it shouldn't be that hard to come up with a concensus on comparing perfromance between NA and European glass packages, but while chatting earlier today with a "glass package" engineer who specializes in Euro standards and practices, his advice was simply don't try to compare Euro and NFRC U values....which honestly is a very common response.

    However, and that consideration aside, when comparing Euro and NA glass packages using the same basic glass substrate, comparable (high solar heat gain, low solar heat gain, etc) LowE coatings, and keeping airspace depth and fill consistent, you aren't going to have any real differences in energy performance, no matter where the glass package was produced.

    Bottom line is that glass is glass, doesn't matter if it floated in Europe or in NA (just as long as its low iron versus low iron or standard soad-lime float versus standard soda-lime float). Euro argon and NA argon comes from the same source no matter where it comes from. LowE coatings are pretty amazing - both application and performance - but there is no one in either Eurpoe or NA who has cornered the market on some new miraculous LowE coating technology.

    Once again, your points are absolutely valid, I agree that the glass packages listed do exceed the performance of what's generally available in NA. But my point earlier is that there is no inherent technological advantage, it's really a matter of what people are demanding from the window suppliers and what the window suppliers want from their glass suppliers. We might spell the difference between euro and NA as "EDUCATION".



Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |