Need To Dry Out House Before Winter
by Henri De Marne
Question: We recently replaced our wooden windows and storms with vinyl replacement windows. We assumed the condensation which caused our windows to rot was caused by too much cold air passing through the windows. However, we wake up now to wet windows and, at times, ice on them. Our house is well insulated and the use of a dehumidifier makes no difference. We use kitchen and bath fans and open windows when possible for ventilation. The problem is worse at night when curtains are drawn, and we can’t leave them open. Any suggestions?
Answer: Condensation occurred on your old windows not from air leakage, but because the dew point was reached when warm, moist air came in contact with cold glass surfaces. The same thing occurs now.
A well insulated, tight house has fewer air changes per hour to dilute the ambient moisture with cold, dry exterior air that becomes warmed once in the house.
In these houses, heating does not operate as often and therefore does not force infiltration to replace the air it blows up the flue.
The newer, more efficient heating systems get their own air supply directly from outside into the appliance itself. Electrically heated homes are even more prone to creating humid conditions since they do not require combustion air. Dehumidifiers are not efficient at the lower temperatures found in homes in winter; they work best at higher summer temperatures. Condensation occurs on windows with curtains and shades drawn because you are isolating warm, moist air in the space behind the curtains and it cools faster and more than the room air which, at night, you probably keep cooler to start with. In spite of your ventilation efforts, you have too high an indoor humidity level and you should reduce it to minimize or eliminate the condensation problem.
Major moisture contributors are bare dirt crawl spaces, wet basements or cellars, firewood stored in a basement, laundry hung to dry, a dryer that’s not vented outside, and large amounts of water-loving plants.
The easiest way, believe it or not, to get cold dry winter air into the house (and humid air out) is to open the doors for a short while.