I was watching a local TV news program about excessive mold growing in a house. They recommended setting the humidistat at 50 percent to stop it. The program was technically correct but misleading. You will not have a severe problem with mold with a relative humidity under 50 percent. Unfortunately, setting your humidistat at 50 percent will not help.
Relative humidity is dependent on the indoor air temperature.
If the humidistat on an inside wall says 50 percent, the air near a cold outside wall or window will be higher. This may result in mold problems. Reduce the humidity level as it gets colder outdoors.