Moisture on windows

We get moisture on our windows at night when it gets cold. Ice even builds up on the inside of the windows if it gets below maybe 10 degrees outside. Our house is 9 years old and is sealed pretty tight. I built some inside storms for one set of windows and that really helped. I was just wondering if maybe a ventilation system, like a Venmar might be a better solution. It is hard to believe we have high humidity in the house in the winter time when the humidity is so low outside and the skin dries out so quickly. I have checked the humidity in the house and don't remember the numbers but it didn't seem very high, like 30% maybe. So why are the windows icing up? Do I need indoor storms on all my windows or is there a better solution?
Andy Arhelger
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I have checked the humidity in the house and

70 degrees, but it is not that low - certainly above the temp near the inside of the window when it is biting cold outside. Therefore, one would expect some ice and condensation inside, especially with single glazed windows, or DIY double glazing, which has leaks.. Finding condensation is common everywhere where you have cold high humidity outside temperatures, with moderate inside humidity. Gas charged double glazing will increase insulation slightly from R1 to R2, and may reduce condensation, but outside of improving inside air circulation, there is little that can be done that will have dramatic results. Keeping miniblinds or curtains slightly open, or raised a few inches above the sill is helpful, as it creates a downdraft along the interior face of the window, which has a defrosting effect.
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Remember dew point? When the temp gets low enough,,,, below freezing any water that is in the air will condense eventually.
Storms inside we had ours outside. Do you have any air movement available? Fans might help.
ISU 1969 temps went to ~ -25 F. We taped card board on the windows in a 60 degree angle and used the space between the card board and the window as a refrigerator. We did not have such things in our dorm then..Grab all the butter pats you could carry so we could have butter on the pop corn later that night.
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30 percent humidity is not high, but if you limit air flow by pulling curtains you will get condensation and ice build up. I assume you have double pane windows, if you don't you certainly will get ice build up if you keep a reasonable temperature inside and you will even with double pane window. Inside storms are ok, but a better solution is outside storm windows especially on the north side.
Andy Arhelger wrote:

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From my aprilaire humidifier manual: They recommend decreasing interior R.H. as the outside temperature goes down by the following table: outside temp (F) inside humidity +40 45% +30 40% +20 35% +10 30% 0 25% -10 20% -20 15%
my experience is that these numbers are optimistic and cutting the humidities in half is not out of the question with cheap windows and cheap storms.

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