Energy adviser: Exhaust fans move air in sealed homes
Thursday, August 11, 2011
Small electric exhaust fans do a lot of work in houses, pulling moist air and heat out of bathrooms and getting rid of cooking odors in kitchens.
It is far more effective, experts say, to quickly eliminate moisture and pollutants when they are created rather than allowing them to dissipate slowly inside your home.
Indoor air can be five times more polluted than outdoor air.
In 1991, Washington’s energy building code regulations were updated to require better air sealing for new homes as a way to conserve energy. Any space where air can enter the home is sealed during construction to limit uncontrolled exchange of air between outdoors and indoors, giving homeowners better control of air flow. Exhaust fans are designed to work in tandem with a home’s central forced-air heating and ventilation system.
Roger Heasley, store manager at Grover’s Electric & Plumbing Supply in Vancouver, said those shopping for an exhaust fan — either in a new home or as a replacement — should keep three things in mind: How much air the unit will pull, operating noise level and price.
“Obviously, quieter and more powerful units will cost more than less expensive models,” Heasley said. “Retail prices can range from as low as $39, up to $154. The more expensive models also may feature built-in lighting.”
Electrical engineers measure air movement by cubic feet of air moved per minute, abbreviated as cfm. They use a measure called “sones” to describe the sound a fan produces. The lower the sone value, the more comfortable the listening environment.
“One sone is equivalent to the sound made by your average refrigerator,” Heasley said.
If you’re getting ready to install an exhaust fan, start by reading the manufacturer’s instructions and following safety precautions. Before working with electricity, turn off the power at the service panel. Make sure your duct work is properly fitted.
If you’re using new duct work, check for the right fit. Buy metal duct work for exhaust and use duct mastic sealant on the joints. Avoid bends and aim for a straight path. Keep duct work as short as possible.
When replacing a fan, buy the same size or one larger than the existing opening — it’s easier to expand a hole than to reduce it. If you’re installing a new fan, you’ll need to cut a hole in the ceiling. But you can make installation a breeze by replacing an existing ceiling light fixture with a fan-light combo.
Bathroom ventilation creates special challenges, because bathrooms are prone to moisture problems. Moisture accumulates on walls, ceilings, and woodwork. Failure to exhaust hot and humid bathroom air can lead to mold and mildew, and it can damage the structural integrity of a building or home.
According to the Home Ventilation Institute, bathrooms should be intermittently or continuously ventilated with an exhaust ventilation fan with a cfm appropriate to the size of the room and type of facilities. An 8-foot-by-5-foot bathroom requires exhaust at 40 cfm. A tub, shower, and toilet require 150 cfm. Jetted tubs need an additional 100 cfm.
Energy Adviser is written by Clark Public Utilities and relies on the expertise of utility energy counselors, who provide conservation and energy use information. Visit www.clarkpublicutilities.com.