Replies

1. 
   Guest_ | Feb 15, 2000 12:48am | #8

   *
   Ok, now for one of my wackier ideas:

   There's no magic behind condensation. Air holds water as moisture. How MUCH moisture air can hold is related to temperature. When warm moist air (inside of your home in winter) meets a cold surface (not so effecient insulated window) you get condensation. Depending on how humid you like to keep your home and how cold it is outside, condensation might be nothing at all to a continuous rain of water.

   But unless you have a failed window, one place you won't find condensation is between the panes of a double (or triple) glaze insulated window panel. Why? Because they suck moisture out of the air when the panel is constructed for that very reason. No moisture, no condensation, no matter what the temperature difference.

   So why not heat the interior side glass surface? It probably wouldn't take but a degree or two if difference to raise inside surface of the glass to a temperature which would prevent condensation.

   The high tech solution would be a factory applied transparent conducting layer right on the glass surface which would be heated electricity. The same technology as is being tested to defrost auto windshields. The controls would measure indoor humidity, indoor temperature and glass temperature to heat the window just enough to prevent condensation. Or maybe even something along the lines of a low intensity heat lamp directed at the glass from the ceiling. Hard to say how the operating costs would add in, not to mention the window cost.

   I also have a low tech solution which would be particularly appropriate to non-opening skylights. If the light well is carefully sealed to prevent moisture coming through the walls and an interior glass pane constructed to create a sealed air space between the skylight and the interior space. I think you could heat the space between the room and the skylight just enough to keep the room side glass from forming condensation. In my case I would consider a small loop off the radiant floor heat system run along the inside walls of the lightwell, setup to provide just enough heat to prevent condensation and no more. This would in essence create a low moisture, room temperature (or slightly less) space between the skylight and the room. Wa la! The major temperature difference has just been shifted from a humid interior surface to a dry "outer" interior surface. No more condensation. And since you're heating a space which would have normally contained heated air anyway, it doesn't even add to the heating load of the house. Heck, if you can drop the temperature of the space a degree or two, you've actually created a better insulated skylight and saved some heating pennies.

   Any window experts out there?

1. 
   Guest_ | Feb 12, 2000 08:09am | #1

   *No window expert here. I think the skylight idea won't work well in practice, because it depends on sunlight. On sunny days, your skylight probably is warm enough anyway to not invite condensation. On cloudy days, when your system doesn't really work, by design, that's when you'll get some condensation.The electric system between panes is good as an idea. Maybe someone would know if this is feasible from an energy/efficiency/$ point of view. My guess is, there's a lot of window panes, door lites, etc. and it would get pretty complicated, plus there's different conditions on each side of the house, under overhangs, trees, etc. So it would be hard to get a reliable system running properly-a lot harder than say, your humidifier/bathroom venting idea.I also believe that those windows would be a huge waste of heat in the sense that you're applying heat almost to the outdoors! But, again, no expert here, just a practical-thinking carpenter who did lousy in chemistry, most math, and never took physics!Still, glad someone's doing some extracurricular thinking around here! Keep it up.MD****************

1. 
   Guest_ | Feb 12, 2000 08:38am | #2

   *Rain-x........... $4.50HIring help to put it on all the galss once a year (includes cleaning which a person willing tospend this kind of moneyis already doing) $120.00 Total $124.50You beat those numbers you've got something.

1. 
   Guest_ | Feb 12, 2000 10:36pm | #3

   *The thing is, any fancy approach is like heat tape on pipes or windshield wipers on eyeglasses, sure it works but better design would avoid the problem. If the windows are terrible I'd put heat-shrink plastic over them. Or move. :)Cool window tech: switchable glazing, turns clear when a current is applied. Marvin sells this stuff ... at about $80 sf! Still...

1. 
   Guest_ | Feb 12, 2000 11:29pm | #4

   *.........if I remember right ...you're in a much colder climate than me...hell, you ain't even got termites (?)ain't you Sakatchewan ??..anyhow...for the most part , I don't have a condensation problem in our houses..and basically it's because of two things...trying not to let the relative humidity get too high... and keeping the glass surface above the dew point...I would guess that both are more difficult than here (say 6000 degree-day winter)... but ..Some of the windows have much higher R-values than others... one of my favorites is HURD, with their triple glazing..Our standard is Andersen High-Performance.... that is the minimum glazing we'll spec on a job...if the house is going to have a hot-air heating system... we'll try to make sure some of the air becomes a window washer...sliding glass doors are notorious. so that warm air does double-duty......sometimes if the weather is around zero, I might notice a little 1/2" strip of condensation along the bottom edge..but it's usually gone by mid-morning (not just my house, but all the houses we've built and/ or done gut/ remodel on)Most often there'll be a little 1/2" square of condensation if the lower corners....anything worse than that and we know we've got a problem..

2. 
   ken_spence | Feb 13, 2000 10:01pm | #5

   *tried several cures, but still have to wipe our new windows daily. nothing stops the condensation

3. 
   Guest_ | Feb 13, 2000 11:37pm | #6

   *....like I said Ken, anything worse and we know we've got a problem...do you live in the mountains, what kind of windows, do you have a damp basement or crawl space? How were the windows installed... is it an old house and new windows?ARe they winyl replacement windows , feel any drafts ?what kind of roof do you have? what condition is it in ?got snow on your roof ?what kind of heating system do you have and what temp. do you keep your house at ?do you run a humidifier ?

4. 
   Guest_ | Feb 14, 2000 09:59pm | #7

   *Wow! Quite a response. Thanks to all who posted.Maybe it does just come down to better insulated windows. Something which has been surprising slow to catch on here (the upfront cost is always the issue, not the continuing comfort).

5. 
   Guest_ | Feb 15, 2000 12:48am | #9

   *Scott:You definitely have a handle on the condensation problem. In my view you are right on that it is a function of interior relative humidity and glass temperature. Another rather homely example is how a camera lens or a pair of eyeglasses fogs over when coming inside on a cold day.My experience is that at cold temperatures given window glass R values there isn't any practical thing that can be done about the problem without endangering occupant health. The typical thing I see when folks tell me they have solved the problem is that they have cranked up conditioned space ventilation to the point that there is essentially zero relative humidity in the house. Obviously, that is hard on occupant health.I have tried several things. At cold temps the only thing I have found to work without unacceptably lowering humidity is to maintain a constant air flow over the windows. One person I know uses a fan that is plugged in at cold temps. Another installation I did was to use forced air heat and put outlets under the windows. Short of something like this frequently wiping the moisture out of the windows seems to be the practical thing to do.