Many people use portable humidifiers in the winter to raise the humidity levels in a home that is too dry. Depending on the outside temperature, recommended levels of humidity in the home vary between 35 and 50%. There are also dehumidifiers that take too much moisture out of the air, which helps create a more comfortable living environment, and can reduce mold growth and dust mites. It is important to clean these units after extend use in either the summer or winter.
You should first check with the owner’s manual of your particular unit. But a good general rule of thumb is to periodically use water and some white vinegar to clean both the water tank, and the base of the unit.
Use a few tablespoons of white vinegar with and swirl it around the tank. Then leave it inside the water tank for about 15 minutes. Rinse out the tank with water to remove any of the vinegar smell. Use a soft dry cloth to dry the unit, and store in a dry, cool place.
Here is a video by Crane USA on this cleaning procedure.