Maintaining Humidity Levels

A certified master home inspector gives tips on how to maintain humidity levels using an in-home humidifier.

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Q: This winter has been especially difficult for my family because of all the dry air inside the home. We used to have a humidifier attached to the furnace, but we had to shut it off because of all the rust it was causing. I tried placing pans of water on registers, but this did not help that much. Should I have the humidifier replaced? What are the alternatives?

A: Not only will the humidifier lead to rusting on the outside of the furnace, but it can rust the interior or damage sensitive electronic components. Unless a built-in humidifier is maintained regularly, mold spores can form on the humidifier grill or inside the furnace fan and ducts. When the fan is operating, these mold spores are spread throughout the home. It is essential to keep indoor humidity levels between 35 percent and 60 percent.

Below 35 percent humidity, static electricity becomes a problem. Your skin cracks and itches, nasal passages dry out, wood inside the home shrinks, and cracks, doors and windows need adjusting. The dry air you're breathing is really uncomfortable.

On the other end of the scale, above 60 percent, mold spores find enough moisture to grow on painted or wallpapered surfaces, windows sweat, condensation forms on cold spots on the north and west sides of the home, and the air you're breathing may be filled with all kinds of unhealthy spores and debris.

Here's how I control the humidity in my home: I use an in-room steam humidifier that has two large containers, which I fill with tap water each day. I prefer the steam units to those that evaporate through a filter. The humidifier has a humidity-control switch as well as an off/on switch. I also use a hygrometer, which is a thermostat that has a humidity indicator. The hygrometer is on my dresser so that I can observe and control the temperature and the humidity in the bedroom.

Why the bedroom? That's where I spend at least eight hours of my 24-hour day. Each bedroom should have its own humidifier because bedrooms have different temperature levels depending on their location in the home.

You should be able to find a simple hygrometer for less than $10 online using your favorite search engine. I found one for $9.95 at a cigar-accessories store, where maintaining humidity levels is critical to the storage of the products.

In-room humidifiers can be found at most home stores and hardware and department stores.

It takes time and effort to fill the tanks each day, but when you see all the mineral deposits and residue left behind when you clean the unit, you'll realize what could have been left unseen inside your furnace or ductwork.

(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home-improvement questions at

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