How important is air duct cleaning? How often should it be done? Is it worth it to pay the extra money to ensure there is no mold in the air ducts? — Angie's List member Glenn G. Millar

Keith Thompson, owner of highly rated Mr. Duct Air Duct Cleaning in Lisle [Ill.], says air duct cleaning should be done once every four to six years, and sooner if you've had recent construction or remodeling. "It'll decrease the amount of dust in the house," Thompson says. "No matter how clean you keep your house, dust always gets into the vents eventually. Cold air returns will pull in debris."

To ensure a quality job, he recommends homeowners hire a member of the National Air Duct Cleaning Association and make sure they follow the residential checklist available at nadca.com. "NADCA and the Environmental Protection Agency both say a duct cleaning runs between $450 and $1,000," he says. "However, Chicagoland is one of the most competitive markets, so some companies will go down to the $350 mark."

Debbie Martinez, co-owner of highly rated Ductastic Air Duct Cleaning in Chicago, says removing mold is worthwhile for health reasons. Her company inspects for mold as a matter of standard procedure when cleaning a duct system. They'll charge extra to clear out mold, using special techniques such as mold-killing ultraviolet lights. "Regular air-duct cleanings will prevent mold from ever building up," she says. "When we find mold, it's usually because the system hasn't been cleaned in a while."