My raised ranch is 21 years old as are the Andersen windows, almost all are double hung. I've been battling window condensation for years and am at the end of my rope! Virtually all the upstairs windows get about an inch or so of condensation on the glass along the bottoms of the both interior panes (top & bottom windows) from the late fall through the early spring. I do not experience any ice formation though.

After years of battling, the windows' interior pine has taken a beating and has become black with water and mold staining as the heat, moisture and sunlight appear to be a really good environment for it. Obviously, I'm concerned about how to correct the condensation issue - and am concerned about a potential mold problem. I purchased a hygrometer in the hopes of identifying a high humidity issue but it's been averaging 50% which seems reasonable to me.

Most condensation seems to develop overnight. The house has three zones with forced hot water baseboard heating. Temps at night are 68 in the bedroom zone, 65 in the remainder of the upstairs (overall temps range from 65-68 degrees). Because we primarily face westward, temps in the afternoon can get higher duing the mid-afternoon due to the sun. Two adults, two children 5 and under, two dogs and a turle (water evaporation?) live upstairs. One adult lives downstairs and temps in that single zone are usually 62 but may go as high as 66 on occasion but it's not common. There appear to be no condensation issues downstairs though.

One possible related note. We had central A/C installed upstairs shortly after we moved in 15 years ago and have noticed that we feel cold air coming from the registers during the off-season, although it doesn't seem to impact the room temperature. We were told not to worry about it becuase the contractor said it was a "closed system" and that our warm air was only cooling slightly and reciculating but I wonder if this somehow contributes to the condensation problem. Should I be the covering the registers and/or return in the offseason? Might I have a leak? Is it even related?

I'm lost, out of ideas, and feel like I am watching my windows deteroriate around me.

Am I in need of new windows, is my central A/C to blame, is there something I'm missing?

Please help!!

Thanks in advance.
Mike