Our house was built in the 70s and we bought it new. I dont know if this has been happening all this time and I have just noticed it, but in the winter only water collects in the HVAC ductwork. I can feel this water if I take off the vent cover and put my hand in the duct. This water collects expecially in the bends of the ducts.
I dry out the ducts as far as I can reach, but this is only a short distance. I am concerned that if the water remains further up in the ducts that mold will grow.
I have been battling this problem for several winters and have found that what dry out the vents in using the central heating (electric) for 45 minutes/day. Before I found this problem, I rarely used the heater because the house is in sacramento, CA and it doesnt get very cold here.
Another thing that helps is to use a dehumidifier to get moisure out of the air. The relative humidity in my house is 60-75% without using the dehumidifier/heater. I know this because I bought a hygrometer.
I open the window/turn on a fan when cooking/using shower, but this doesnt help.
I dont know if this problem is due to some leak in the house or something that I'm doing wrong.