The hall bath vent occasionally will have damp drywall around the fan.
4 March 2006
A. You have diagnosed your problem very well. You have two things going on and the solution to your basic problem will be a combination of efforts. Itís hard for me to argue against the use of whole house humidifiers especially now that my largest compl aint has been remedied by the industry with the addition of ultra-violet (UVC) light sanitizers into the system to keep the production and dispersal of mold, mildew and bacteria down. You probably donít have such a device on your system but you havenít mentioned that anyone is chronically sick in the house during the season of humidifier use.
I wonít bother to go into explanations about sensible heat of heated air augmented by latent heat of moisture introduced by the humidifier creating a sense of greater body comfort at lower temperatures or the avoidance of those annoying little static ele ctricity shocks you get at light switches and such when the airís really dry because you know that-- thatís why you bought the humidifier in the first place.
But I do see humidifiers gone wild pumping excessive moisture into houses through malfunctioning controls or sticky valves gummed up by minerals deposited from evaporating water or even leaking humidifiers that drip water onto the ductwork ultimately rus ting things out. Go take a hard look at your humidifier and make sure itís not doing anything like that. If you are seeing condensation on your windows then your interior humidity levels are pretty high, assuming you have insulated (double pane) glass in your windows. Donít believe those settings on the humidifier controls. They are guesses at best. Buy yourself a cheap hygrometer at the hardware store and monitor the humidity levels in your house. You donít want readings above about 45 percent re lative humidity (RH). 35 percent RH or so at the maximum should do just fine. If things are really out of whack with your humidifier, go take a look at the underside of your roof on a cold morning on the side of the house that gets the least sun. Iíve seen attics dripping wet with humidifier moisture and owners thinking the roof was bad. Well, not yet, but itíll rot soon if that condition isnít brought under control.
Now that youíve got the humidity under control, keep an eye on that hall bath vent. Itís not uncommon for the vent grille to become cold due to air leakage and that can provide the cold condensation surface that will collect moisture and wet the drywall . In some cases the cold ducts leading from the bath will condense warm moist bathing exhaust air and if the duct is angled just right, drain the condensate back to the bath. I wouldnít entertain the idea of cutting a roof vent just for that bath. Any h ole you cut into a roof can give you trouble, so the fewer the better. Frequently I see baths on the second level vented with ductwork that lays over the insulation and dumps out at a vented soffit. You might consider that but Iíll bet things will strai ghten themselves out when you get the humidity under control.