Leave your humidifier off.

As a home inspector in the Stillwater MN area, I see a lot of whole house humidifiers. They are the boxes on the side of the furnace. They have a few low-voltage wires attached, and a thin water line. Somewhere, usually near the thermostat or attached to the furnace, is a small box that is about the same size and shape as a thermostat. It will have a dial that offers high, medium or low.. That box is the control for the humidifier. The way it works is simple; when the moisture in the air drops below a certain level (set by the dial- stay with me here), a valve opens up, letting a small amount of water to run down an evaporator pad. The air moving through the furnace picks up the moisture, increasing the humidity in the house. Sounds good, but hold on.

Dry air has been blamed for loose floorboards, nosebleeds and static electricity. Bringing moisture in the air does indeed reduce those problems. The problem is, moist air CAUSES some problems, too.

High levels of moisture in the air can cause frost on the windows in the wintertime, leading to decay of window parts and damaged walls, including insulation. Have you ever seen stains on the lap siding that look like the house has been crying? Sometimes, you can see actual icicles coming right off the siding in the winter. This could be the result of ice dams, where water runs down the inside of the walls. It could also be a result of very high moisture levels in the house. Remember science class? (me neither) Heat goes to cold, moisture goes to dry.  Moisture can also lead to high levels of mold. Certain kinds of mold grow when relative humidity is 55% or higher. Bedbugs? 65%.

If you’re like me (and I know I am!) you’ll see that the problems outweigh the benefits.

There are some alternatives.

If someone is sick, and sleeping is easier when the air is moist, there are small vaporizers that can be used at night and turned off during the day.

Some musical instruments react poorly to low moisture levels. They can crack and warp. Sometimes pianos cannot be tuned properly because the low moisture has caused the sound board to warp beyond repair. Good news; There are products that can be installed in the piano itself that will help control moisture levels, although they are not cheap; $600. for that reason, make sure you need one by buying a hygrometer for about $10, and try keeping a leafy plant nearby first. I found an interesting article by someone named Ask Andy.) Why, oh why did the Andy family name their kid Ask? I’d hate to see HIS therapy bill!) Click: Mr. Andy talks about moisture

AprilAire makes a sophisticated device that takes into account the outside temperature and self-adjusts. You can learn more by clicking AprilAire Whole House Products


Share The Story

About the author

Joe has many years of experience as a Home Inspector. Joe is a proud member of ASHI, MAHI, WAHI & SAAR. He follows the Best Practices as described by the American Association of Home Inspectors and the Wisconsin Association of Home Inspectors. He is licensed in Wisconsin and is Radon Certified. Joe also complies with ASHI's Code of Ethics.


  1. What should my humidity level be, and how do I know if I need a dehumidifier?

    • Joe Lundequam says:

      I’m glad you asked, and sorry that I didn’t see you question earlier.

      Most homes are quite comfortable when the humidity levels are relatively low.
      Humid air holds more heat. That means that a warm summer day is more comfortable when the humidity is lower, and sweat can more easily evaporate.
      Hot air can hold more moisture, so a window will more likely be a source of condensation (leading to frost) on a cold day. The moisture in the air condenses on the cool glass. The water runs down the window and brings dirt from the glass that can harbor mold. The moisture can also damage any wooden components of the window.
      But to your question; Buy a hygrometer for around $20 at a hardware store. The RH (Relative Humidity) levels should be 40%-50%, but lower than 40% might be best during the winter months, if you see frost building up on the windows.
      Most molds grow at about 55%, some a lot higher. BTW, bedbugs prefer around 65%.

    • Joe Lundequam says:

      You can buy a hygrometer for about $10 at a home center. The target RH (Relative Humidity) should be 35% – 50%.
      Most molds grow at about 55%. (Bed bugs thrive at 65%, in case you care.)

      During the winter months, less than 40% might be needed to avoid condensation issues. If you see frost on the window panes, the moisture level might be too high. Remember to keep the window shades open during the day to let the windows dry out.

      If your dehumidifier is running constantly, consider finding and eliminating the moisture source. A lot of people don’t use the bathroom fan, or for long enough. A timer in the fan switch could be installed. If you ran the fan for 45 minutes after taking a bath or shower, the moisture in the house could be a lot lower.

  2. Great post, my name is ron spinabella and i run a great blog and twitter account. I’m going to repost it for my followers.

Leave a reply

Your email address will not be published. Required fields are marked *