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Thread: Patio Door, Low E glass vs Clear glass

  1. #1
    DIY Member thegallery's Avatar
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    Default Patio Door, Low E glass vs Clear glass

    I have a patio door that gets direct sunlight around midday, but because of evergreen trees and a huge hill it's maybe only an hour a day.

    I want to replace the current patio door because the current one is 40 years old and my office desk is now right next to the glass. I sit 24" from it. Plus I open it 10 times a day for dogs to go out. There is no way the current one will do anything but freeze me out all winter.

    But in the replacement I have a choice of clear glass or Low E. The Low E is $100 more, which sounds like a bargain. The door has an r value of 2.0 and with Low E it has 2.8. I don't know what all that means but it sounds like it is 1/3 more insulating.

    but is that only for sunlight? and does Low E really insulate better? Basically, is the LOW E coating for real or for just a worthless add-on?

  2. #2
    Engineer garyl53's Avatar
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    Go for the low-E. It made a huge difference in a west facing office in our house. It also will help reflect the heat back in the winter.

  3. #3
    Master Plumber Dunbar Plumbing's Avatar
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    Low E I thought was the gas they put between the panes.


    That way, when the sun shines through the glass, it doesn't magnify and create hot spots when you have ac on.

    I've definitely witnessed the difference between how they work, and they work well.
    Read what the end of this sentence means.

  4. #4
    DIY Senior Member molo's Avatar
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    Windows are very complex these days. I would reccommend some research.
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
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    DIY Member thegallery's Avatar
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    I did some research! Low E stands for Low Emissivity. The general consensus is that it really is effective. It's kind of like layering the window with foil, except that it is so thin you can see through it.

    Adding Argon gas I did not research but that adds even more insulation. I'm just not sure it makes as big a difference. I'll check on pricing though.

    This patio door's ratings are:

    U Factor

    Clear Glass - 0.51
    LoEČ Glass - 0.37
    LoEČ/Argon - 0.33

    Here is the Wikepedia entry on Low E:

    Low-emissivity
    From Wikipedia, the free encyclopedia

    Low-emissivity (Low-E) coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. The principal mechanism of heat transfer in multilayer glazing is thermal radiation from warm surfaces to cooler surfaces. Coating a glass surface with a low-emittance material reflects a significant amount of this radiant heat, thus lowering the total heat flow through the window. Low-E coatings are transparent to visible light, and opaque to infrared radiation. Different types of Low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain.

    To make Low-E glass, certain properties such as the iron content may be controlled. Also, some types of glass have natural Low-e properties, such as borosilicate or "pyrex" (tm). Specially designed coatings, often based on metallic oxides, are applied to one or more surfaces of insulated glass. These coatings reflect radiant infrared energy, thus tending to keep radiant heat on the same side of the glass from which it originated. This often results in more efficient windows because: radiant heat originating from indoors is reflected back inside, thus keeping heat inside in the winter, and infrared radiation from the sun is reflected away, keeping it cooler inside in the summer.

    [Low-emissivity coating][1]

    Low-emissivity (Low-E) glass has a thin metal coating on the glass within its airspace that reflects thermal radiation back into the interior, and allows solar radiation into the room. Thus, the coating helps to reduce heatloss but allows the room to be warmed by any ********.The low-e coating is on the inside pane of glass, if solar control is required then the outside pane of glass would have either a film or a body tint to reflect solar radiation. The principle of operation is similar to the greenhouse effect where short wavelength radiation is transmitted through the pane, but longer wavelength radiation is reflected.

  6. #6
    Plumbing Designer FloridaOrange's Avatar
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    I have Low-E double paned, argon gas filled windows in my house. After moving in I will not ever go back to regular windows if I can help it.

    Keeps out heat (probably cold too but it doesn't really get cold here) and sound very well. I don't think you'd regret the extra expense. If you do go with something like that make sure you get commercial rollers though.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    The coating reflects heat...in the summer it keeps it out, in the winter, it reflects the house or your heat back. You will be signficantly more comfortable. Plus, it also blocks a fair amount of UV, so things don't fade as much.
    Jim DeBruycker
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  8. #8
    DIY Senior Member MG's Avatar
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    I concur w/the Low-E - I've been replacing our old windows w/double pane and Low-E and it makes a big difference. Our power company increased rates dramatically this year and our bill only went up a bit compared to those increases. I also replaced our patio door and that difference was remarkable.
    Note: I am a DIY'er and not a professional. My posts here are observations / opinions and may or may not be in accordance with your local ordinances.

  9. #9
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Low-E is good. If anyone knows of a company with a double- or triple-pane, low-E slider, approved for Florida, 12' long, let me know.

  10. #10
    DIY Member theelviscerator's Avatar
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    Some people just don't like the look with current generation LOW E glass, a bluish to grey silver tint.

    Next gen should look almost like non low e glass.
    The world is a grindstone, whether it wears you down, or polishes you up, is up to you.

  11. #11
    In the Trades AZ Contractor's Avatar
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    Low E helps block the ultraviolet radiation from entering your home. It will help protect furniture from getting discolored from the sunlight as well add an insulation factor to your window.

    I hear that argon gas fill windows are a waste. After a few years the argon leaks out and you spent extra money for nothing.

  12. #12
    Plumbing Designer FloridaOrange's Avatar
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    Quote Originally Posted by AZ Contractor View Post
    Low E helps block the ultraviolet radiation from entering your home. It will help protect furniture from getting discolored from the sunlight as well add an insulation factor to your window.

    I hear that argon gas fill windows are a waste. After a few years the argon leaks out and you spent extra money for nothing.
    You'll know if the gas leaks out of the windows......they'll start to get condensate on them. Mine are 8 years old now and no problems to date, except for the slider rollers, d@mn things are heavy and if the track gets dirt in them it could do a number (which is why I recommend the commercial rollers).
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  13. #13
    Plumbing Designer FloridaOrange's Avatar
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    Quote Originally Posted by Mikey View Post
    Low-E is good. If anyone knows of a company with a double- or triple-pane, low-E slider, approved for Florida, 12' long, let me know.

    I'll look for the mfr. tag on mine, the slider I have is a 6 foot pocket. They were code in '99, don't know about now.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

  14. #14
    Jack of all trades frenchie's Avatar
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    Quote Originally Posted by Mikey View Post
    Low-E is good. If anyone knows of a company with a double- or triple-pane, low-E slider, approved for Florida, 12' long, let me know.
    Nanawall. Pricey, but they're the only hurricane-rated I can think of, that wide. And they fold, rather than slide, so you can open up the whole thing.

    If you're willing to go with two 6 footers, or some such combination - just about everybody's got one: Andersen, Pella, etc.
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  15. #15

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    thegallery,

    Low E windows are going to greatly reduce the amount of sunlight that passes through the window usually by about 45-50% if you tell me what direction the door faces we can do a calculation on how many BTU's you will get in potential sunlight compared to how many BTU's you will lose with the reduced R value window to see if there is any solar gain. My best guess would be that the Low E is the way to go

    Lou

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