Window Curtains

Hey guys and gals,

Have a simple question. Say your windows are properly sealed, should you get heavy curtains to keep warm air in at night? What I'm asking is, do windows lose heat? Can air escape through windows? I have hear that windows are not good at all for colder climates...comments? Anyone wanna share what kind of curtains they have? :)


  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Window Curtains
    NewLady wrote: »
    Hey guys and gals,

    Have a simple question. Say your windows are properly sealed, should you get heavy curtains to keep warm air in at night? What I'm asking is, do windows lose heat? Can air escape through windows? I have hear that windows are not good at all for colder climates...comments? Anyone wanna share what kind of curtains they have? :)

    That's why dual & triple pane insulating windows are made, the cut down noise, and are thermal insulators.

    Storm windows were the fore-runners of dual glaze.

    Curtains & drapes may help a bit, but a sheet of stryofoam or the like would be better, harder to store though.
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  • BB.BB. Super Moderators, Administrators Posts: 32,814 admin
    Re: Window Curtains

    Yes, Windows are terrible for heat loss and heat gain... An insulated wall is probably 20-40x better insulated than a typical window.

    R19-R40 for walls and ceilings... Windows are rated in U (approximately=1/R) and run from ~0.5 to 0.15 (really good ones) or R=2-6.6 and typical good double pane windows are around U=0.25 (R=4)...

    Here is a quick link with some numbers...

    On two houses now I have replaced my old single pane wood and aluminum windows with double pane vinyl (myself). Reduced heat gain/loss by a lot, reduced outside noise, and drafts. Replaced them on another home (insulated) and a small apartment building (no insulation, both paid contractor) and the owners were very happy too.

    My climate is pretty temperate (SF Bay Area), and I was amazed at how much summer heat gain was prevented. We have a couple west facing bedrooms in an uninsulated (walls, stucco outside) home. Both rooms used to be very hot in the summer afternoons and I replaced the windows with double pane, low E glass, and the rooms barely ever got warmer than the rest of the home after that (just ceiling insulation and concrete slab floors).

    I would bet that double (or triple pane) windows in cold climates would help a lot. However, if you have a "wall of glass" and have problems with heat gain/heat loss--you may wish to consider removing 1/2 the glass and redesign the home with smaller windows (or adding shade/trees/etc. depending on your specific issues). Very good insulated windows are still going to have an R value of 4-6 and even a 2x4 wall with fiberglass is going to be R-19--much better insulation.

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  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Window Curtains

    Bill stole my thunder, but I will add one more point. The R-value of a window ASSUMES a film of still air on the inside AND the outside of the glass. Take away that still air and you dramatically increase the heat loss. Any wind on the outside, or draft from fans, furnaces or movement on the inside takes away that film. (I'm hard pressed to think of an environment that has neither event, more likely both)!

    Glass itself is a VERY poor insulator, but a very good conductor of heat. The major insulating value of a window comes from the AIR SPACE between the glass. You do have to be careful however, because if the air space becomes larger than about 3/4" and the window is large, you can get a convection loop from the inside to the outside. Since the glass is such a good conductor, these losses can be significant. You also feel chilly and can even feel a draft in front of a large window because the window is convecting so much heat off its face to set up a draft in the room. Air may not be escaping or infiltrating, but you can feel a convective draft in the room anyway.

    I am of the opinion that in most cases triple glazing is a looser. For the price, you are way better off adding insulation to the ceiling or the walls. Having said that, the idea of insulated curtains/pop in panels, or even duette type shades makes a huge difference. We have insulated window quilts on all our windows, and close them most nights. At -30F the frost rises to the top of the glass behind the quilts, and can be 1/2" thick in the morning. (Thats an insulated window to boot!) Even a simple curtain can preserve the inside film of air, as well as providing some r-value.

    A quick btu calculation using Bill's number will tell you in a hurry how much your glass is costing you. Thanks for the calcs Bill.

  • System2System2 Posts: 6,290 admin
    Re: Window Curtains

    Thanks for the info guys, think I will opt for heavier curtains. Also, just to mention I live near Niagara Falls, Ontario. Where the temp can range from -20 in the winter to +35 in the summer. On that note...does the color matter. I mean, we all know that black attracts heat. So would it be dumb to have the back color black in the winter then switch to white in the summer?:confused:
  • System2System2 Posts: 6,290 admin
    Re: Window Curtains

    A little different take on windows.
    Living in Nova Scotia, we do have some cold winter weather for sure.
    To take full advantage of the suns free heat in winter, I have NO windows on the north end of the house, only one small one on the west side and a couple of small ones on the east. The south end however, which does face due south, is almost all double pane glass. This was done precisely to take advantage of the low in the southern sky, winter sun's heat. And I have to tell you that it works AWESOME! In fact, 2 years ago, the big windows had to be replaced, so while I was at it, I got larger ones, increasing my southern glass area by 25%!
    This had dramatically reduced my winter heating costs. No matter HOW COLD, or WINDY the winter day, if the sun is shining, I have no heat on at all, and the inside temp easily hits 88F and soaks into the drywall and everything else. The sun during much of the winter is gone by 4:30, yet it's usually 10 PM before the house cools down to 72F and I have to think about lighting the wood stove. In summer, the suns heat does not come in the southern windows, because during that time of year, it's high overhead, not low on the horizon like in winter. I pull curtains over at night,and all in all, with this settup, the reduction in heating costs is fantastic. On those cold but sunny winter days, with no heat on and sweltering in almost 90Finside temp (you can always open a window, but why throw away free heat?) I look out across the hills and see the smoke pouring out of chimneys everywhere, as furnaces and stoves hump their guts out trying to keep those houses warm. I remember my dad used to say that he could almost hear the wood rattling as it made it's way up his chimney. Haha
    Never any solar heat gain on the north end, so no windows or openings of any kind, just solid, well insulated wall. Very little solar gain on east or west, so small windows. Huge gain on the southern, so huge windows.
    I LOVE IT and after 25 years experience, would never want it any other way. That's why 2 years ago, I expanded the area of southern windows.
    Now if you're living in a hot area of the world, that's a whole different thing that I have no experience with.
    All the best
  • System2System2 Posts: 6,290 admin
    Re: Window Curtains
    NewLady wrote: »
    Thanks for the info guys, think I will opt for heavier curtains. Also, just to mention I live near Niagara Falls, Ontario. Where the temp can range from -20 in the winter to +35 in the summer. On that note...does the color matter. I mean, we all know that black attracts heat. So would it be dumb to have the back color black in the winter then switch to white in the summer?:confused:
    Interesting you should ask that.
    On my south facing windows, I have TWO sets of aluminum venetian blinds on each window. In winter, I drop the black ones, have them tilted up and open a bit, and on sunny winter days, the heat just pours out of them and into the room. Any day I don't want free winter heat, I lift the black ones and drop down the white ones. VERY pleased with this system.
    I would be concerned about blocking off the windows with dark curtains on sunny winter days, because there could be a huge buildup of heat next to the upper part of the windows and may crack the glass. Probably wouldn't. but I don't want to try.
    On very cold winter nights I drop them both, to provide a double dead air space between the glass and the room.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Window Curtains

    adding to wayne's comments here i must say that if you intend to collect solar heat from the sun that you should not buy windows with a low e coating on the windows that would block heat going into the house and not just out of the house. the curtains would work well in conjunction with south facing dual glazed windows without the e coating. open in the day to let the heat in and close them at night to keep the heat in and for privacy too of course.

    on the subject of color most agree that dark colors would absorb the solar heat well, but few realize that in the absence of the sun that it will radiate that heat faster than a lighter color. seeing as how the curtains are open during the day to allow the room to suckup the heat, the curtain's colors don't come into play, but at night a darkly colored curtain could allow more heat to escape than say white or lightly colored curtains. light curtains could help to keep a room cooler in the summer too as it would reflect more of the heat away rather than absorbing it and keep in mind the summer sunshine is so intense that it need not be direct to absorb heat.

    as to the windows themselves, if they leak air at all they are no good. even the heaviest curtains (recommended in colder climates) can't stop cold air very well that has leaked through the window itself as it will fall straight to the floor and sets up a draft. the old storm windows do not stop air well at all and i recommend replacing such windows. north facing windows can have that e coating as no solar will be absorbed during the day and you want none to escape at night. this may also apply to some windows more to the east or west as well for the winter warming sunshine does not bode well from those 2 directions, but the summer sunshine will enter windows on the east and west faces quite easily and you don't want that. argon gas dissipates quickly from inside a window much like the helium in a helium balloon would escape though not quite as fast as a helium balloon and i think it's a waste.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Window Curtains


    You got the basic passive solar down. Good design. Other ways to help with summer heat gain is mass in the heated space (helps year round!) eaves that are calculated so that they shade in the summer and proper trees for the summer. I have the same basic set up, little north glass, a bit of east and west, with lots of south.

    Having said that, the point of insulating the glass so that the days heat gain is not lost over night. Every btu you can keep in the building the better. As to New Lady's thought about dark and light. Since the shades would be open during the day, there would be little advantage in the heating season. Light coloured on the outside facing would help with heat gain in the summer.

  • daledale Solar Expert Posts: 29
    Re: Window Curtains

    Nice summary of the convection heat loss. Everyone has told me that argon isn't worth the cost since it dissipates in a few years.

    I have found that double pane windows with an insulating strip between the panes work. These were put in a 1920 brick house with lathe and plaster walls. There was no insulation. After changing the windows, they were noticeably warmer than the walls. We now have Pella's with a higher rating, but they feel cold compared to our others.
  • peakbaggerpeakbagger Solar Expert Posts: 341 ✭✭✭
    Re: Window Curtains

    I have a couple of brands of double cellular blinds installed on my double pane Anderson Windows. In general they work well but getting side tracks makes a major difference. As my standard units fail I will be switching over to the side tracks. Easiest way to explains side tracks is this link

    Its quite noticeable with the conventional blinds that have gaps on the sides and the base that there is a lot more convective flow between the window and the blind. In very cold weather, I see less condensation forming on the inside of the window with the side tracks than with the standard units.

    I have bought several of the side track style from the linked firm and prefer them as the hardware they use is far heavier duty than those supplied by the standard cellular blinds. I think its important to get heavy hardware if someone opens and closes them daily when the sun is out as my experience is the standard cords and hardware at best lasts 2 years.

    I have a couple of standard cellular blinds that I will have to replace because of cheap lifting hardware. If the string breaks, it is very difficult to replace. I tried replacing a broken string after buying replacement parts and string on the web and once I took the header apart discovered that all the plastic parts are cheap and not designed to be taken apart. The standard string system is threaded across the top of the window and then down the length of the blind to the bottom of the blind. The heavy hardware has a shaft that runs across the header and the shaft is turned by a heavier braided rope.

    Of course these aren't cheap and probably long payback, but it really makes a room more livable.
  • SkippySkippy Solar Expert Posts: 308 ✭✭
    Re: Window Curtains

    With my windows (or most of them) I have covered them with the same 2 inch styrofoam that I used for covering my refridgerator . . I just leave it there year round. . . mainly because I live in a town, and like being able to walk around / get out of the shower - without worrying about who might be walking by my front windows.

    Yes, it does cut down on the amount of light in the house, but it cut down on the heating bill (winter) and cooling bill (summer).

    Quick test for ya - take off your shirt - stand in front of the window - cold - put the blinds down - warmer ? - stick in a chunk of styrofoam - MUCH better :)

    Just my 2 cents.
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