If neglected, these units can spew out a lot of undesirable bugs – bacteria, mold and mildew – that promote allergies, asthma and other illness. Your goal is to kill the bugs off, or at least make life extremely difficult for them. Periodic disinfecting and scrubbing does the former; drying helps with the latter.
At the very least, remove and drain the water tank after each use, leaving it open to dry out as much as possible. Unplug the heating unit and drain as much water as you can, allowing it to dry out before the next use.
Once a week, disinfect the tank using 1 ounce (30 ml) of chlorine bleach per gallon (3.8 l) of water. Let the tank sit for 10 minutes, sloshing the solution a couple of times. Scrub, drain and rinse with plenty of clean water until bleach odor is gone.
Scrubbing is necessary to remove any biofilm (a fancy name for the protective slime that develops on the inside of humidifiers that is resistant to most germicides).
Clean the heating unit at least once a week if it's used daily. First unplug the unit. Remove scale by filling it with undiluted vinegar, or equal parts vinegar and water, briefly turning the humidifier on to heat the vinegar, then turning it off. Allow the solution to work for at least 30 minutes. Use a soft brush, such as an old toothbrush, to scrub away remaining scale and all other surfaces that come into contact with water. Rinse thoroughly and allow the unit to dry before using.
Unless you live in an extremely dry climate, you may be able to reduce, or even eliminate, use of a humidifier. Sealing a home by installing or replacing caulk and weatherstrips — and taking other measures to block air infiltration in the basement and attic — will help your home retain more humidity. House sealing tasks may be performed by either do-it-yourselfers or contractors.