At What Humidity Level Should One Set a Dehumidifier?

In cold weather when a heating system is in use, the RH level should be kept between 30 and 40 percent. Otherwise, condensation can form on windows. Relative humidity levels above 50 percent are more likely to allow bacteria to grow. Some dehumidifiers do not have components that monitor humidity level. The Energy Star program recommends the purchase of a hygrometer, which independently reads the humidity level of a room and guides the homeowner to turn the dehumidifier to the on or off setting.