A. Energy and sustainable design consultant Andy Shapiro responds: Two factors affect the humidity level in a house: how fast water is being introduced and how fast it is leaving. A very tight house doesn’t need a lot of moisture input to result in high humidity and condensation on the windows, while the same amount of water introduced into a very leaky house won’t raise the humidity much.
You can use a blower door to check the house air leakage rate, though your wet windows may already be telling you that it is relatively tight. You can also check the humidity in the house with a Radio Shack temperature-humidity indicator. The windows should tolerate 40% relative humidity without condensing in cold weather. If they don’t, then...
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