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Understanding NFRC site Low-E Information

oldbungalow | Posted in Green Products and Materials on

Hi there, poking around on the NFRC site to x-shop windows (JW Siteline Clad vs Marvin Integrity FG/FG vs Integrity FG/Wood)
Can someone explain the Low-E information on the site? For a particular configuration it says “0.022(2) 0.149(4)”. This one the configuration I’m looking at, on the Siteline it yields U0.24 and SHGC0.18, similar code on Marvin yields about the same, U0.25.

I don’t know how to translate this into an “orderable” configuration though, and when I click the pop-up on the NFRC site nothing happens. I’m guessing the parenthetical numbers refer to number of surfaces, so 4 might mean a room-side coating?

The document “NFRC_CPC_Code_Listing” does not explain.

Also, related, when I go into the Marvin site, below, I don’t see casements under Integrity, not sure why or maybe my browser doesn’t show.


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  1. Expert Member
    BILL WICHERS | | #1

    Those are the surface numbers the coatings are applied to. Surface numbering starts with the exterior (outdoor) surface as #1, then the side of the outer glass pane that is inside the window’s internal air space is surface #2, the side of the inner (indoor) pane facing the windows internal air space is surface #3, and the interior (indoor) surface of a double pane window is surface #4.

    If you are looking at a triple pane window, surfaces 5 and 6 are the inner airspace side and indoor sides, respectively, of the innermost pane of glass.

    A “surface 4” coating on a double pane window is an exposed coating on the indoor side of the window, probably cardinals i89 coating or something similar. I would let them apply coatings to the surfaces they recommend and not try to rearrange things.


    1. oldbungalow | | #2

      Awesome, thanks! That's really helpful. So I'm guessing the values before the surface numbers denote the emissivity (sp?), with lower value indicating more "reflective".

      I think there are pros/cons to the room side coatings, i.e. condensation/cleaning hassle, depending on Zone.

      1. Expert Member
        BILL WICHERS | | #3

        I have found this document:
        To be very useful regarding coating specifications. Note that this is for cardinal glass IGUs, but the basic concepts are the same for everyone (physics is always physics :-)

        I89 effectively lowers the surface temperature of the innermost pane of glass and that means you’ll get interior condensation at higher outdoor temperatures than you otherwise would. There is some detail about that in the document I linked, as well as a handy chart. Cardinal claims the coating is just as durable as the uncoated glass would be, with the one exception that there are certain types of cleaners that you must not use.


        1. oldbungalow | | #4

          Great reference, thanks!

          The doc actually decodes the last piece of the puzzle, the chart on Page 3 lists LowE coatings and their emissivity. 0.022 is their LowE3-366 coating. 0.149 is their LowE-i89 product (which is indeed the indoor lite coating).

          So the Marvin window I was looking at has that combination.
          Looks like all the 0.25 to 0.27 U factor options have that combination. At 0.28 they have the 0.022 366 coating on one inside surface only. Not a huge tradeoff (drops from R4 to R3.6), and condensation resistance jumps from mid 40s% to 59%.

          The Jeld Wen listings are much easier to understand now that I figured it out, the product code provides all the clues. They seem to offer a lot more of the coating permutations than Marvin.

          Curious if anyone has had any experience with fogging/scratching of interior coatings.

  2. Expert Member
    Peter Yost | | #5

    Hi KT -

    It's relatively new for window manufacturers to use low-e coatings on exposed surfaces. But our low-e storm windows of course have exposed low-e coatings to the interior and for the last 18 years plus, we have been moving these glass panes about and cleaning them. They are sort of a "gritty" texture but nary a scratch.


    1. oldbungalow | | #6

      Thanks Peter, I think those storm window coatings you describe are likely hard (pyrolitic) coatings, but my understanding is i89 (surface 4 low-e) is not really a hard-coating (not pyrolitic).

      From Cardinal: "LoĒ-i89 is an improvement to the previous LoĒ-i81® by improving light transmission in the monolithic form by approximately 8%. The patented LoĒ-i89 coating is an Indium Tin Oxide (ITO) coating applied by the sputtering process."

  3. Expert Member
    Peter Yost | | #7

    Thanks K T -

    You are right; my low-e coating is hard coat. Interesting to learn that new technology means exposed sputter coatings are possible.


  4. thrifttrust | | #8

    Just a note: I don't think you will find it on their website, but JW Siteline Clad windows are available triple glazed. They should provide a U value in the .18 range.

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