Indoor Humidity Levels
The following list, supplied by the Minnesota Department of Public Service, is based on a double-glazed window and an indoor temperature of 70 degrees. You will notice that the lower the outdoor temperature, the lower the indoor humidity should be.
• If outside temperature is 20 to 40 degrees, humidity indoors should not be more than 40 percent.
• If outside temperature is 10 to 20 degrees, humidity indoors should not be more than 35 percent.
• If outside temperature is 0 to 10 degrees, humidity indoors should not be more than 30 percent.
• If outside temperature is 10-below to 0, humidity indoors should not be more than 25 percent.
• If outside temperature is 20-below to 10-below, humidity indoors should not be more than 20 percent.
• If outdoor temperature is lower than 20-below, inside humidity should not be more than 15 percent.
If you are building a home or remodeling, demand high-quality windows. They should have U-values of 0.35 or less. Such windows are less prone to cold-weather condensation and icing, which means that indoor humidity can be higher.