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Window heat loss

Post in 'The Green Room' started by chuck172, Jul 10, 2010.

  1. chuck172

    chuck172 Minister of Fire

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    I'd like to resolve what I think is a big heat loss in my house. Windows.
    I have 20 year old Anderson double paned units. They are O.k, but I really don't have any insulated window covering. Insulating shades, curtains etc.
    What's everybody using?

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  2. benjamin

    benjamin Minister of Fire

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    Unless your house is extremely well insulated, I'd doubt that these windows are a signifigant heat loss. Especially if they really were built in 1990, as opposed to the former owner claiming they were twenty years old when you bought the place 15 years ago.

    They may be clear glass which loses much more heat than low e, but unless they're really leaky (major wear or bad install), and/or they're rotted out, there is no way you would save money by replacing them or adding insulating curtains.

    If you just want to add curtains, and aren't doing it for the money then go for it.

    I have lots of old double pane clear glass (all facing south-gains more heat and loses more heat) and smaller low e on the other sides. No curtains yet either.
  3. chuck172

    chuck172 Minister of Fire

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    I built the house with new windows in 1990. They are double paned andersons. I have alot of glass. No curtains, great views. I love the solar gain on the south facing units during a sunny day, but at night I'll bet they equal a big hole in the wall proportionate to their size. I have a big bow window and a sliding glass door that has to let out my valuable Tarm heat. I'll do anything I can to make my minimal (500 gallon) storage work better.
  4. DaveBP

    DaveBP Minister of Fire

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    Modern low-e double-glass well sealed windows are only achieving an average R value of about 3. So just imagine all of the area of the windows being simply uninsulated 2X4 wall.

    Is it worth insulating that wall? Sure it is, if it is simply a matter of stuffing some cheap fiberglass in there. Unfortunately, the laws of the universe require that anything having to do with windows have to be the most expensive materials in the entire construction project.

    The other problem with windows is that most good insulators are opaque. No problem at night but you need to remove that insulation in the daytime.

    For a few years I put 1" urethane rigid foam panels over my big window wall units. I feel guilty as hell about it but the inconvenience of handling all those panels (and where to put them during the day) caused me to use the foam in another project and just put the effort into cutting a little more firewood to make up for the heat loss. However, this year I am moving into the house that I've been building for too many years. Much more glass area in some rooms so I'm thinking about foam panels for the rooms that aren't occupied during the day. Leave them there until we want to use that room.

    I've concluded that anything you use to insulate windows has to be very convenient or you end up not using it.
  5. benjamin

    benjamin Minister of Fire

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    I'm in the same boat, insulating shade/panels would make a huge difference when it's 20 degrees and cloudy for a week. But then you're going to have the boiler going anyway. Curtains would probably keep my place warmer when it's sunny and really cold outside at night, but I stay comfortable enough without them in that kind of weather.

    If the shades allow you to burn once a day instead of twice, you may enjoy putting them up rather than lighting another fire. On the other hand most people light their fire in the evening and it might not make that big of a difference in the useful storage if the boiler is covering most of the nighttime load directly, it would be a matter of putting up the curtains or another load in the boiler.


    One more thing to get around to when there's nothing better to do.
  6. chuck172

    chuck172 Minister of Fire

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    If that thermostat calls for heat less frequently with curtains at night then curtains at night is what I want. Any heat save is heat used later when needed and that extends my storage time. Like I said, I have minimal storage, I don't want to add anymore and I want to stretch the storage as far as possible.
  7. Dune

    Dune Minister of Fire

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    A long time ago, Mother Earth News had an article about insulated curtains. They made them with blankets stitched between drape material. You would also want them pretty secure to avoid air touching the window glass. Maybe velcro strips along the sides, weighted at the bottom, and closely fitted at the top. I can't see how it could not help.
  8. vvvv

    vvvv New Member

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  9. chuck172

    chuck172 Minister of Fire

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  10. begreen

    begreen Mooderator Staff Member

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    If the house has high heat loss, new windows may offer one of the poorer returns on investment. A decent single pane window (with tight glazing in good condition) + a good storm window = R 2, so going from R2 to R3 is not going to net a big savings gain. You would need to upgrade to some serious, arctic design triple pane windows to really affect heat loss through the glass. Curtains, shades or panels can make a quick difference with a faster payback.

    For a better ROI, aggressively seal up all leaks, starting with the foundation sill and work upwards. Make sure door and windows are sealing well too. Then insulate every where possible, including the joist spaces above the sill. Then add insulated curtains, multi-cell shades or removable panels and you will start seeing some real gains.
  11. Delta-T

    Delta-T Minister of Fire

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    I've seen people around placing aluminized mylar (emergency blanket basically) over their sliding doors. Never asked how well it worked. Those things reflect high percentage of radiant heat, though I'm sure that heat loss from windows is more likely to be conductive. Anybody know anyone using something like that?
  12. vvvv

    vvvv New Member

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    Czar's configuration + modification would result in a foam panel with aluminum facing, overlsized so to create dead air space + foil & reflective gain to r-value. 2" foam can get up to r-15 on the glass! as seen the lower panel remains in place for ease of use but system can be further modified. lower panel in place allows for running around with no pants on!
    hard to sell brains to a genius!
  13. willworkforwood

    willworkforwood Feeling the Heat

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    This seems to be a subject that everyone is interested in these days! We have lots of glass just like you Chuck. Before getting the idea for the boiler, I built 22 storm windows 4 years ago out of Plexiglas and plywood frames. Not a quick project, but it has helped a lot. I can post pics if anyone is interested. The storms averaged $26 each, so the thermal drapes would probably be both easier and less expensive. We also bought floor-length thermal drapes to cover a French door, and that gives a huge improvement in that part of the house. In addition to the storms; a couple of years ago, I realized that the top and bottom window seals were getting old and losing efficiency. I replaced them, 2 being done on a cold, windy Fall day and it make an immediate, noticeable difference in the area around the window. So, it became obvious to me that this job should have been done at least a few years earlier, in order to avoid the gradual loss in efficiency. My windows don't have side weatherstripping, but I know that other models do, so that's another thing that would need replacement over time. These window seals aren't an obvious thing, because they're not something out in plain sight, like door weatherstripping is. It's a good thing to check every few years.
  14. semipro

    semipro Minister of Fire

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    We tried some insulated cellular shades (with side tracks to seal the side) in one room. They seem to work well and are well made. I believe the name is "Comfortex ComfortTrack Plus". The side tracks and top and bottom seals stop convective air leakage around the sides.
  15. Floydian

    Floydian Feeling the Heat

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  16. chuck172

    chuck172 Minister of Fire

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    That is a great site Floydian, thanks.
  17. jebatty

    jebatty Minister of Fire

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    Just about the wisest thing my wife and I did back in 1992-1997 was replace all the windows in our 1956 house with quadruple pane equivalent windows (two panes of glass with two layers of plastic film between the glass panes), low-e, argon, etc. They also are coated to block infrared heat from coming in during the summer and trap infrared inside during the winter. These are rated R-8 and were expensive. We have about 62' lineal of glass in a 160' perimeter house, most windows are 5' high, and we really wanted to preserve the outside views. I doubt they ever will provide an investment payback in $$$, but the payback in comfort is priceless. No cold air wash in the winter, no drafts, and even with -30F and colder outside with howling winter winds, the glass on the inside is warm to the touch. Also, no frost or condensation. The wood around the glass is free of any water staining. With all the money a person spends on other items of comfort, in the right situation spending big bucks for comfort from great windows just might be worth it.
  18. chuck172

    chuck172 Minister of Fire

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    I have the same glass/house perimeter specs as jebatty. No window covering, just 20 year old double pane andersons. Money is tight but I have to come up with a good answer.
  19. oldspark

    oldspark Guest

    I have some 30 year old double pane Anderson's and I have no intention of changing them out or do I feel the need to make a cover for them. Had some other funky windows changed out but I think the Anderson's do a good job. I have a Passive solar house and when we built it we were going to make some insulated coverings for the big south windows but it never happened (like a lot of things), I was using the plans out of a magazine called New Shelter (great magazine) and I do think on older windows they can make a big difference.
  20. Dune

    Dune Minister of Fire

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    That is a great site! Thankyou very much. I am going to be spending a lot of time there.
  21. dogwood

    dogwood Minister of Fire

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    You might take a look at the low-e window films they have at Lowes. I'm not sure how much insulation value they impart. We have been adding film onto our twenty year old Anderson double hungs to protect our furniture and curtain fabrics by preventing UV infiltration without regard to the added insulation value. The manufacturer is Gila. The film goes on easily with a squeegee. Check out their site: http://www.gilafilms.com/Residential/residential-window-film.htm

    Mike
  22. chuck172

    chuck172 Minister of Fire

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    I looked at the site dogwood, I don't think the film adds to the r value of the windows. As a matter of fact the film would probably reduce the daytime solar gain of the glass. Looks like a great product to block the harmful uv rays as needed in your case though.
  23. DBoon

    DBoon Minister of Fire

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    You might want to check your library for an out of print book called "Movable Insulation" from Rodale Press. It's a good resource that would allow you to put a lot of facts behind your decision.
  24. jebatty

    jebatty Minister of Fire

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    This article might be helpful to you, just appeared in the Minneapolis Star-Tribune: Windows
  25. midwestcoast

    midwestcoast Minister of Fire

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    +1. You could also just get an energy audit & take the guessing out of where to get the most bang for the buck. The guessing part is kinda fun though.
    Storms are much better on a ROI basis (especially DIY storms). Thermal shades or curtains need a reasonably tight fit to walls or tracks. I think 1/8" or less space to keep convection down.
    If you're set on new windows get the best you can afford. Quality double pain, low-E, argon replacement sash kits are a cheaper alternative to full replacement windows if your frames are in good shape. I put in some sash kits & with storms now have ~R4 on most windows, but I don't think it saves me much. Windows are the most obvious source of heat loss 'cause they're so close & visible, but they are generally far from the biggest.

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