Patio Door, Low E glass vs Clear glass

Discussion in 'Remodel Forum & Blog' started by thegallery, Oct 25, 2007.

  1. thegallery

    thegallery New Member

    Messages:
    30
    Location:
    Philly, Europe
    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. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    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. 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.
  4. molo

    molo Member

    Messages:
    845
    Location:
    cold new york
    Windows are very complex these days. I would reccommend some research.
  5. thegallery

    thegallery New Member

    Messages:
    30
    Location:
    Philly, Europe
    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
    LoE² Glass - 0.37
    LoE²/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. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    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.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,023
    Location:
    New England
    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.
  8. MG

    MG New Member

    Messages:
    160
    Location:
    Illinois - Near St. Louis
    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.
  9. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    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. theelviscerator

    theelviscerator New Member

    Messages:
    72
    Location:
    Elkhart, IN
    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.
  11. AZ Contractor

    AZ Contractor In the Trades

    Messages:
    90
    Location:
    Phoenix, AZ
    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. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida
    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).
  13. FloridaOrange

    FloridaOrange Plumbing Designer

    Messages:
    1,317
    Location:
    SW Florida

    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.
  14. frenchie

    frenchie Jack of all trades

    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.
  15. BigLou

    BigLou New Member

    Messages:
    138
    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
  16. Oberon

    Oberon New Member

    Messages:
    5
    first post

    this is my first post to the forum, and it is long - sorry...

    There are two primary types of window coatings available - pyrolitic or hard coat - and soft or sputter coat.

    Softcoats are multi-layered coatings consisting of several different metallic oxides with silver as the primary heat-blocking ingredient. Softcoats are applied in vacuum chambers to finished glass.

    Hardcoats or pyrolitic coatings are applied to the glass while the glass is still semi-molten in the tin bath portion of the float process. Basically, the bottom side of the glass will have a coating of tin from floating in the bath (as does all float glass), but the topside will also have the layer of (primarily) tin oxide - which is the LowE coating.

    So in one sense, glass with a pyrolitic coating has two "tin-sides", but one - the LowE side - of them is much thicker than the other, although only one coat affects energy performance.

    Often, the pyrolitic coating is applied to the #3 surface of an IG unit if the unit is intended for use in a heating-dominated climate - but not always since there are also solar-reflective pyrolitic LowE coatings that are applied to the #1 or #2 surface of an IG unit to reflect solar heat gain in cooling dominated climates.

    Sputter LowE coatings are also applied to the air-side of the glass, primarily because sputter coats adhere better to the air-side, but also it is possible for the slight metallic (tin) layer on the tin-side to affect the performance of the coating.

    A sputter coat is applied in multiple layers, it may be about 7 to 11 layers, depending on the coating. People really don't realize, or can appreciate, how thin a typical sputter LowE coating is. Sputter coat folks measure the thickness of each metal oxide layer, as well as the finished coating, in angstroms, or by how many atoms thick the coating is. A typical softcoat LowE coating is generally less than 1000 atoms thick.

    Sputter coats are generally applied to surface #2 of an IG unit, although they can also be applied to surface #3. Consider a typical IG unit - two lites of glass separated by a spacer.

    The exterior of the exterior (as you said) is surface #1. The interior of that lite is surface #2. The other lite then has surface #3 and #4 - with #4 being the surface that is actually exposed inside the home.

    In a heating dominated climate, there are two reasons for placing the LowE coating on the #3 surface of the IGU. First is to allow for solar heat gain in the winter and second to block the transference of the heat inside your home to the outside.

    Which brings us to High Solar Heat Gain (or HSHG) coatings and Low Solar Heat Gain (or LSHG) coatings…

    What does that mean? Well, all LowE coatings are designed to block far - or longwave - infrared energy. This is the range that includes typical household-produced heat. This is also the frequency range of heat that is produced when the sun warms an object – the heat you feel when you touch the sidewalk on a hot, sunny summer day. While direct solar energy is shortwave IR, the heat released by a sun-warmed object is longwave IR…and hopefully that made sense.

    A typical hardcoat or single-silver layer softcoat works in this application since both types of coatings block the far infrared energy - thus keeping winter heat indoors - but neither is designed to be effective at blocking shortwave infrared - thus "allowing" solar heat access to the home - winter or summer.

    Placing a high solar gain coating on surface #3 maximizes the level of solar heat gain thru the IG unit which can be an advantage in winter and can also be a disadvantage in summer.

    A Low Solar Heat Gain product, on the other hand, is designed to block both near and far infrared energy. It will keep heat - including direct solar gain – from passing thru the window in both summer and winter.

    These coatings are placed on surface #2 to maximize effectiveness against direct solar gain by blocking solar heat before it can pass into the airspace in the IG unit – and into the home.
    Last edited: Nov 23, 2007
  17. thegallery

    thegallery New Member

    Messages:
    30
    Location:
    Philly, Europe
    Wow Oberon, that was some post! I haven't checked the Wikipedia entry for Low E in a while but I reckon a lot of your information would go well there.

    I have the typical home window glass as you mentioned but not sure which of the two versions I have. I went with American Craftsman 9500 windows at Home Depot and they say, "U Factor: LoE² Glass - 0.35". I did not get Argon filled ones.

    I'm not sure if they are the greatest windows in the world but they seem to work great. I did the Patio door a couple weeks ago and all eight windows last weekend (yes, quite proud of myself!). It's impossible to tell how effective they are but compared to the previous dilapidated aluminum single paned windows I sense already that the heater is firing up less than normal. The patio door, which work next too, is a huge difference. The interior glass is still cold to touch, but I'm sure not half as cold as before.

    Thanks again for your post. I'll have to get it a couple more reads to let all the info sink in!
  18. thegallery

    thegallery New Member

    Messages:
    30
    Location:
    Philly, Europe
    Lou, sorry I missed this post. So I ended up doing the Patio door with the LoE. It was $360 including screen from Home Depot.

    Because of the huge hill right behind me I only get maximum 3 hours of direct high angle sunlight in the summer and no direct light in the winter. It is pretty light though because the sun is just behind the trees. I just doesn't get hit directly. The door faces South West. It's a standard 6' door and rated with a U factor of .37.

    Wouldn't you know that the stock window was 1/8" larger than my opening! So I had to re-frame one side, (which was just as well as I found some rot in the bottom). But added to the when I pulled out the old door the concrete sill had deteriorated so I had re-concrete the sill too. (I'm hoping the repair will last at least 10 years). Anyway, the job is done and my dogs are happy. It's so much easier to open, and I can't feel any air coming through.
    Last edited: Nov 23, 2007
  19. Oberon

    Oberon New Member

    Messages:
    5
    good morning thegallery,

    LowE really does work. Some folks would suggest that LowE is simply a marketing ploy to get more money from the consummer, but as you have seen the addition of LowE in a dual pane window really does make a difference.

    As a general comparison, the interior glass temp of a single lite window when it is 0 degrees outside and 70 inside is going to be about 16 degrees. Add a storm window or go to dual pane window and that temp jumps up to about 43 degrees.

    Add LowE and that temp jumps up to about 53 degrees...so while the glass still feels cool to the touch, it is a good bit warmer than before and as you have already noticed it makes a difference in the room.

    Enjoy
  20. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,714
    Location:
    Central Florida
    Wouldn't any thermally conductive surface below body temperature feel "cool" to the touch? If I take a glass tumbler out of the cabinet it's at room temperature, but definitely feels cool.
Similar Threads: Patio Door
Forum Title Date
Remodel Forum & Blog Alside Patio Doors Jan 17, 2012
Remodel Forum & Blog Patio Cover Rebuild Oct 27, 2009
Remodel Forum & Blog Good Source For Door Hardware Sep 15, 2014
Remodel Forum & Blog Framing a door Mar 25, 2014
Remodel Forum & Blog actual door opening width Mar 19, 2013

Share This Page