Energy Adviser: Exhaust fans help clean up indoor air



When you spend your hard-earned money heating or cooling the air inside your house, it can seem like a waste to blow that air outside with exhaust fans. But it’s necessary for good indoor air quality, which otherwise can be five times more polluted than outdoor air.

“Using exhaust fans isn’t so much an energy issue as it is a mold and mildew issue,” said Bob West, a Clark Public Utilities energy counselor.

Energy conservation measures such as sealing windows and doors make homes tighter, which hinders ventilation. That’s where fans come in. Exhaust fans are designed to work in tandem with a home’s central forced-air heating and ventilation system.

The small, electric exhaust fans in your bathroom, kitchen and laundry room suck moisture and pollutants out of your house as they are created, so they don’t disperse throughout the building.

That’s only when exhaust fans are working properly, however.

“Some fans make a lot of noise, but don’t do very much,” West said.

Test your fan by taking one square of toilet paper and placing it underneath the unit. If the fan can’t keep the piece of paper aloft, it may not have enough suction to draw moisture out of the bathroom. You’ll need to replace it with one that can do the job.

When shopping for exhaust fans, you’ll want to keep an eye out for two measurements. Sone describes how loud a fan is; the lower the fan’s sone value, the quieter it is. That’s more of a preference issue. A fan’s effectiveness is measured by how many cfm, or cubic feet per minute, of air it can move.

The Home Ventilation Institute recommends a fan that moves at least 1 cfm per square foot for bathrooms of 100 square feet or smaller. The absolute bare minimum, according to the institute, is 50 cfm. For bathrooms larger than that, the institute recommends adding capacity for every fixture: 50 for a toilet, 50 for a shower, 50 for a bathtub and 100 for a jetted tub.

If the range in your kitchen is against the wall, the institute recommends an exhaust fan that pulls 100 cfm per lineal foot of the range, or at the very least, 40 cfm per lineal foot. If your range is in an island, you’ll need an overhead fan with even more capacity — 150 cfm per lineal foot, but no less than 50 cfm per foot. Fans pulling air downward have different capacities so ask your contractor or our energy counselors for recommendations.

It’s not enough to just have the fans. You have to actually use them.

“It’s important to run the fan until the moisture is completely out of the room,” West said. In the bathroom, that can mean running the fan for an hour or more until the shower walls are dry. You can cut the operating time by using a squeegee to first remove excess water.

“If the fan shuts off and all that surface water is still there, the water will find its way into the air again,” West said.

If you have to rush off to work after showering, and don’t have enough time to clear moisture from the bathroom, West recommends replacing the fan’s wall switch with a timer. You can just set the timer for an hour or so, and then be on your way knowing that the fan will click off on its own — and help your home will stay free of mold and mildew.

Energy Adviser is written by Clark Public Utilities. Send questions to or to Energy Adviser, c/o Clark Public Utilities, P.O. Box 8900, Vancouver, WA 98668.