06:10AM | 12/22/04
Member Since: 12/21/04
1 lifetime posts
HELP! Can anyone explain why we have window condensation if our indoor humidity level us at 27% when the outdoor temp is between 0-10??? The recommended level is 25-30% for this temperature.We are at our wits end!!!The house is 44 years old and this is our first winter in it. We had our heating contractor bring over one of his expensive humidity gauge to make sure that ours was providing a reasonable accurate reading. The condensation has turned to ice and it is going to rot the wood on our casement windows if we don't find a way to solve the problem. To add to our confusion is that we have a sliding window in a bedroom and a patio door in the kitchen that have storm windows and there is no condensation on them (very minimal if any). One window company told us that casement windows are the tightest fitting and therefore there is condensation on the them because the warm moist air is being trapped. The heating contractor told us with our humidity level being in range, the cause is leaking windows (cold air coming in from the outside). We cannot run the dehumidifier any more because it is as low as it will go (35%), everything is vented properly, we use the kitchen and bath fans during showers, etc. etc...all the things you are told to do to reduce indoor humidity. It seems like it is impossible to determine which problem we have, high humidity or bad windows but we would like to try to figure out which one it is as either option to correct the problem is expensive (i.e. heat recovery ventilator or new windows). The part that is most confusing to me is if the humidity is too high, why are the two biggest windows (slider and patio door) not wet when the casements are? I would tend to think that replacing the casement windows with windows that have storms would eliminate the problem if we maintain the proper indoor humidity levels. If anyone has any suggestions/opinions/ideas it would be greatly appreciated.


01:57PM | 12/23/04
Member Since: 06/23/04
161 lifetime posts

For a given humidity level there is a corresponding dew point temperature. This dew point is the temperature at which the moisture in the air will condense on cool objects (dew on the ground when the air cools in the morning or condensation on a glass of iced tea when exposed to moist air). The lower the humidity percentage, the colder the air temperature necessary to reach dew point. At 30% humidity, 0 to 10 degree air is near cold enough to reach dew point, especially if the windows leak some air. If the surface temperature is above freezing condensation occurs in the form of water droplets or dew. If the surface temperature is below freezing condensation occurs in the form of frost or ice.

Your bedroom windows probably don't ice up because the storm window and the inner window together act as an insulated assembly. The arrangement provides an air temperature between the pair that is cooler than the inside temperature but warmer than the outside temperature, thus never reaching dew point. If the outside air gets cold enough (say minus 45 degrees) then the air between the two could get down to 0 to 10 degrees and you would have condensation again.

You did not say, but I am assuming that your windows are single pane (not insulated glass). Adding storm windows over your existing windows should solve the condensation/icing problem unless your existing windows leak a lot of air. To make a test, pick your worst case location and add a storm window over the existing window. If you like what you see, upgrade the remaining windows.

Another possible solution is to blow inside air onto the glass surface of the windows (with a fan or redirected air duct grilles). Assuming that the inside air is reasonably warm (60- 65 degrees), the surface temperature of the glass will rise thus preventing condensation. This is one reason you will see air ducts located in front of all windows in better commercial buildings.



11:01AM | 01/24/05
Member Since: 08/25/03
3 lifetime posts
I agree with everything that the 'brave' man before said, however I do have one further solution for you to try. When I was a young kid, we had a window facing the north that leaked all the time, even with a storm window on it. It always had moisture on the inside, standing water on the sill, and when really cold out, it iced up to the point you could not even see through the window. The window sill and sash continued to become more and more black. We bought some of those 'window insulator kits' from 3M that you can get at **********, *******, etc. Just use the double sided tape that comes with it, cut the clear plastic to size, tape it on, and use a hair dryer to seal it tight. After we did that, we only had a very small amount of moisture on the inside of the window pane, no standing water, no ice. It was unbelievable how well it worked. After 2 or 3 months, we had to 're-tighten' it with the hair dryer again. But, this was extremely helpful and an extremely 'cheap' method. I think you can cover about 5 average size double hung windows with the kit we bought, and I don't think it was more than $15 to $20. I haven't priced them lately, but it did miracles and this window was pretty drafty. I lived in Southern Wisconsin, so we had several months of this type of temperature difference between inside and outside.

Good luck, and let me know how it worked if you try it.



08:23AM | 12/16/13
Here is my personal experience: If you have blinds or curtains pulled, the air in the room won't circulate and condensation -- even ice -- will form. This will happen no matter what brand of windows you have. Mine are Marvin wood/clad, which are some of the best. In my situation, I had a bedroom on the upper level of my house that I kept closed and blinds drawn. I thought I was doing a good thing, energy wise, but it made condensation and ice form in winter. I finally tried raising the blinds and leaving the door open and no more condensation problems! I also suspect that showering and cooking while not running external exhaust fans exacerbated the situation.

Anyhow -- for more info -- Andersen Windows has a really great video that helps explain condensation, why it happens, and how to prevent it (I am not employed by Andersen, nor sell their products).

For those who don't want to bother watching the video (it's only 3 min long), here's the take-away:

"Condensation doesn't mean there's a problem with your windows. In fact, the presence of condensation could actually be a sign that your windows have good, tight seals. Everything that makes homes more energy efficient also locks moisture inside your house and increases the chances of condensation forming."
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