It usually costs more than $1,000 to have your home's air ducts cleaned properly — but is it really worth it?

Maybe, says the U.S. Environmental Protection Agency, noting there isn't much research regarding air duct cleaning.

Definitely, say other indoor air professionals, citing a litany of conditions - including years of accumulated pet dander, dust balls and dirt - as reasons why homeowners should consider a cleaning.

Investigate options

Every day, Americans inhale mold, chemicals, dust, pollen, pet dander and a cloud of other indoor contaminants. The problem is so pervasive the EPA lists poor indoor air quality as the fourth-largest environmental threat in the country. The problem can be worse in the winter, as cold weather keeps people indoors with the windows tightly shut.

According to the National Air Duct Cleaners Association, duct cleaning can help if you have pets, if someone in the house smokes or if there has been water damage. The group, however, stops short of saying it can improve your health.

The EPA advises that improper cleaning of air ducts can actually cause problems by stirring up dust, and if you're thinking about having ducts cleaned only because someone in the home suffers from allergies or asthma, you might want to check with your doctor first.

"There are so many things that can trigger asthma," says Dr. Bruce Wolf, an allergist with St. Thomas Health Systems in Murfreesboro, Tenn. "Asthmatics have hypersensitive airways so anything can be an irritant."

Wolf doesn't necessarily advise patients to have air ducts cleaned; instead, he thinks people should consider being tested to see what it is they are allergic to in order to avoid that allergen.

John Schulte, executive director of the air duct cleaners group, says first determine whether ducts contain excessive accumulations of dust, dirt, or even mold. He recommends removing a floor or wall register and pointing a digital camera with a flash inside to take a picture down the duct.

"It's a great way to check," Schulte says.

He warns consumers to be wary of cleaning companies pushing for the use of sanitizers or anti-microbial chemicals. "Unless there is serious contamination of some kind, a regular cleaning is going to do the job," he says.

Costs start at about $500 for a smaller home, he says, and can run more than $1,000 for a larger home. Homes with two or more heating and cooling systems may cost more.

How it works

Duct cleaning can take six hours or more, says Carl Greenway, owner of Ductz Indoor Air Professionals of Williamson County, Tenn. Workers will bring in a negative air machine, a huge vacuum-like device that attaches to the furnace.

"We turn the furnace off and instead of air being blown into the home, we use the negative air machine to suck air back through the duct work," Greenway says.

If technicians do their job correctly, Greenway says, it shouldn't be necessary to cover any furniture, unless there is an air vent directly above a computer or other electronics.

Along with the ducts, technicians have to clean the whole HVAC system, says Joe Roland, owner of Steamatic of Nashville, Tenn. "That means the coils, the drain pan, the air plenum, the heat exchanger, and the blower motor and assembly," he says. Not cleaning each part of the system properly can cause a lot of damage to the home and even the HVAC system, he says.

Protect your home

If you're going to spend the money to have the system cleaned, take steps to protect your investment. "You've got to think about what's generating dust and particles into the air," Roland says. "Things like dander from your pets or lint off the dryer."

Properly maintain your HVAC system; an annual inspection helps ensure adequate air intake and peak efficiency.

And don't skimp on the type of filter you buy: The air duct cleaners group reports that inexpensive, 1-inch fiberglass panel filters do little to remove contaminants from the air. Try a high-efficiency pleated filter instead. And change them a minimum of every three months, Roland says.

"And if you can, consider vacuuming the lint off the dryer, not just wiping it," he says.

On the Web:

www.epa.gov, Environmental Protection Agency.

www.nadca.com, National Air Duct Cleaners Association.