How Much Humidity Should Be Maintained In The House During Winter?
When the outside temperature is at freezing (32° Fahrenheit or 0° Celsius) or above, indoor air should be kept at a humidity (amount of moisture in the air) of 35 percent to 40 percent. When the outside temperature decreases to 150 Fahrenheit (9° Celsius), indoor air humidity should be maintained at 30 percent. At 0° Fahrenheit (-180 Celsius), indoor air humidity may drop to about 20 percent.
To determine if the humidity in your home is adequate, place three ice cubes in a glass of water and allow them to stand for five minutes. If the room has adequate moisture in the air, then plenty of condensation—beads of water—will form on the outside of the glass. If condensation does not occur within 5 to 15 minutes, the room is too dry.
Sources: Heloise. All New Hints from Heloise: A Household Guide for the '90s, pp. 314-15; Whitman, Roger C. More First Aid for the Ailing House, p. 191.