Problems With Too Much, Little Moisture

Special to The Times

QUESTION: I read somewhere it’s recommended to set the bathroom fan to run 20 minutes past your shower to make sure all the moisture is removed. The article also said to use the kitchen fan anytime you use the stove, because moisture trapped inside the house is bad. My problem is I have a terrible time with my house being too dry! I suffer from dry lips, throat, nose, etc. I was told to reduce these effects I should place bowls of water beside the furnace vents to add moisture to the air.

I’m now confused . . . should I be running fans to remove moisture or placing pans of water near the furnace vents to add moisture? Please set me straight.

ANSWER: Too much or too little moisture in the indoor air is a problem for many homeowners.

Dry air can lead to health problems, increased static electricity (oops, there goes the home computer!), cracking of furniture joints and finishes, and other problems. On the other hand, too much moisture in the air can cause other health problems, mold growth and severe structural damage. Moisture levels should generally be maintained between 30% to 60% relative humidity.


Two major factors determine whether the indoor air is too dry or too moist; the amount of moisture being generated indoors--or entering the house from the outside or soil, and the amount of moisture that escapes or is ventilated out of the home.

The average family of four generates about two to three gallons of water vapor per day from activities such as bathing, laundry, breathing of occupants, dish washing, etc. Since most existing houses were not fully air-sealed during construction, this moisture quickly leaks out and is replaced by cooler, drier air--creating the dry-air conditions that you’re experiencing.

Houses built tightly, or subsequently weatherized (air-sealed), allow the occupants to control indoor moisture levels because the houses are able to retain the moisture. If the moisture builds up too much, the occupants simply turn on an exhaust fan. The amount of time fans need to run depends upon the fan size and the amount of moisture needing to be removed.

In your situation, you are either producing too little moisture through your day-to-day activities--or the moisture is being lost to the outside through the use of the bath fan and kitchen range hood, or by air leakage through the building shell. Air leaks in the furnace duct system can also contribute to loss of moisture.


Assuming you’re generating a typical amount of moisture, you shouldn’t immediately add lots of additional moisture. Instead, attempt to retain the moisture to a “leaky” house can have some severe consequences--moist air that leaks into walls and ceilings can condense and cause insulation to become damp and lose some of its insulation value. Moisture in these areas can also cause exterior paint to peel, siding to warp and lead to rot and structural damage.

Next, don’t automatically run the bath fan and kitchen range hood. Let some of the moisture recirculate through the house (your thermostat may have a “fan only” switch that will let you use the furnace blower to help mix the air). You’ll discover it’s easy to regulate the moisture level in your house by balancing fan operation with moisture production.

Leaks in furnace duct systems can dry out your home and are extremely wasteful from an energy standpoint. Check your ductwork to ensure all the connections are secure and the joints and seams are sealed. If the ducts are not sealed or insulated, you should upgrade as soon as possible. Energy savings will often pay for the cost of the materials in a very short time. Seal all the joints and seams, including where the ducts meet the floor at the registers. Use an approved brush-on sealant instead of duct tape. Insulate the ducts after sealing is complete.

Prepared by the Education and Information Network of the Washington State Energy Office.