Indoor relative humidity of 50 percent and a temperature of 70 degrees imply a “dew point” of about 50 degrees. In many households a 50-degree temperature may well be measured in back of an electric outlet, on the floor of an upstairs closet, etc. These surfaces will be wet. Mold may follow. Bathroom and kitchen fans are needed to keep local humidities under control. A milk carton, removed from the refrigerator, will have a surface temperature of about 40 degrees. If it “sweats” while on the kitchen counter, the humidity in the kitchen is about 30 percent — that’s high wintertime for an old house.
Posted Oct. 18, 2008, at 2 p.m.