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Aluminum windows

analytical newbie | Posted in Energy Efficiency and Durability on

Hello! Building our home with our own hands at 7400 ft in a special wind zone in Wyoming. I’ve got lots of questions for you, as I’m gathering loads of helpful info from your site, but I’ll start here with windows. Aluminum windows are used in this region and in other cold/extreme environments for commercial buildings, many of which are concerned with their thermal envelope. And yet, aluminum, thanks to its high thermal conductivity, is not recommended for residential windows – even thermally broken ones. Why? Doesn’t the conductivity issue get entirely resolved via the thermal break? Please help? B/c otherwise, I am in LOVE with the durability & the relatively low expansion coefficient of aluminum vs other materials. Fiberglass’ thermal expansion coefficient is the same as glass – HOWEVER, Fiberglass windows are not/cannot be 100% fiberglass – they are a composite of fiberglass & some kind of polymer. So, the expansion coefficient becomes hazy. Aluminum’s is simply twice that of glass… Thank you for any insights you can provide.

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  1. GBA Editor
    Martin Holladay | | #1

    Most homeowners prefer windows with wood, vinyl, or fiberglass frames, because of their thermal characteristics. But if you want to buy aluminum windows, go right ahead. It's your house.

    Here are links to manufacturers of windows with thermally broken aluminum frames:

  2. analytical newbie | | #2

    Hi Martin - thank you for your quick reply. I would really appreciate, however, if you would provide your opinion on whether thermally broken aluminum windows can still be faulted for thermal conductivity issues. Can you think of an argument against thermally broken windows?!!

  3. analytical newbie | | #3

    Oh, and I haven't checked with any of the suppliers you mentioned other than Milgard, who restricts their thermally improved windows market to the southwest region since, according to my sales rep according to them, is "b/c aluminum windows just don't get high enough U-values." I'm still trying to find the basis for this!

  4. GBA Editor
    Martin Holladay | | #4

    Low U-factors are better than high U-factors. A research paper looking into ways to optimize the thermal performance of window frames concluded that lower U-factors can be achieved with wood window frames or vinyl window frames than with aluminum window frames.

    Here is a link to the paper: Thermal optimization of window frames.


    "The Uf-value of the reference model of the vinyl window frame is 1.503 W/m²K. It is possible to reduce it to 0.759 W/m²K or a reduction of 50% by choosing the right combination of optimization techniques....

    "The reference [wood] frame has an Uf-value of 1.640W/m²K and by combining the appropriate techniques, an Uf-value of 0.584 can be obtained."

    "Table 2 reports the different optimization strategies applied to the aluminum window frame model with a thermal transmittance of 2.775 W/(m²K). The lowest achievable Uf-value by combining these strategies is 1.210 W/(m²K), a reduction in heat loss of 56%."

  5. GBA Editor
    Martin Holladay | | #5

    The Milgard sales rep is ignorant. You want a low U-factor, not a high U-factor. But the rep is correct that aluminum window frames are a poor choice for cold climates.

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