This is my first post and I hope I have the formate correct, I live and build in central Pennsylvania. I built a house in 2004 using what I thought were the best practices at the time to insure it was tight and very well insulated. Took great pains to properly vent all bathrooms, dryer and range. I used Tyvek house wrap and a 6 mill vapor barrier on walls and ceiling. Used a pre-fab basement wall system that creates a very dry basement. Customer works for a propane gas co. and had a high efficiency gas hot air system installed. They are having a very hard time with condensation on their windows in the winter. They are very unhappy with me because they feel the house is to tight and I should remove the plastic vapor barrier. The only thing I changed was using Crestline windows instead of Anderson. As a side note I built 6 new homes using all of the same building techniques in my area and had none of these problems. We have discussed the use of exhaust fans allot and they assure me they use them. It is just Mom, Dad and a teenage girl so not an excessive amount water usage. What should the RH be in the winter and should I just buy them a de-humidifier. Oh, Yea they do have a heat recovery system they use when the temp reaches 50 degrees. Any help would be welcome.