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  1. #1
    Join Date
    Jan 2012

    Default Adding insulating value to existing windows

    I built a frame out of 1/2" x 1 1/2" material I ripped from 2 x 6 lumber. I added shrink window film to a frame I build and then installed the frame with the shrink window film approximately 4 inches from the glass in 6' x 5' windows. What is the best distance to install the film that is attached to the frame from the glass? If the film is to close to the glass, the R-value will be small. If the distance is to far from the glass, eddy currents will form and decrease the R-value. I call the manufacturer but received no useful information.

  2. #2
    Join Date
    Jan 2008

    Default Re: Adding insulating value to existing windows

    Based on your description I doubt that much matters as there will be enough air leakage to negate any difference in the enclosed area. That's not saying they won't help- they most certainly will.

    R-1 equals one inch dead airspace, R-2 two inches etc. You'd have R-4 if both the window and the storm were essentially airtight- that's highly unlikely here. Your main gain is from loss of direct conductivity through the glass as well as slowing the total air movement, thus the actual R- factor is much less of an issue. Just set them where they will seal decently and are easy to install and remove, then enjoy the savings!


  3. #3
    Join Date
    Dec 2007

    Default Re: Adding insulating value to existing windows

    You are correct in your assumptions. According to "From the Walls In" by Charles Wing, the optimum spacing is 3/4"(0.75"). If you use a mirrored tint on the exterior glass, you will increase the r value some more.

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