Dear Jim: I see many ads about furnace duct cleaning. Our children have allergies and get colds. How can I determine if the ducts need to be cleaned and how can I compare the various duct cleaning companies? – Ann T.

Dear Ann: Some families can benefit tremendously from having furnace ducts cleaned and other families will notice no significant difference.

Only your physician can tell you what is causing your children’s problems. If poor indoor air quality, molds, etc. are suspected, then duct cleaning may help.

Duct cleaning can also improve the efficiency of your furnace and air conditioner. Proper duct cleaning is more than just cleaning ducts. It also cleans the blower, heat exchangers, cooling coils, and condensate pan. With these elements clean, air flows more efficiently through the entire system.

All ducts are going to accumulate some dust over time. This generally is not a problem that requires cleaning unless your family experiences health problems. A duct cleaning company can inspect the furnace ducts to show you how dirty they are. This is often done with a video camera in the ducts.

If mold is present anywhere in the entire duct system, you should have them cleaned. It is sometimes difficult to determine if ducts contain dust or mold – they look similar. To be certain, a lab can check it for you. This usually involves touching a piece of tape on an inside duct surface and sending it to the lab to be analyzed. The testing often costs about $50.

There are several methods to clean ducts. One method is using an extremely powerful vacuum outdoors in a truck. A long hose is run to the furnace area and attached to the ducts. From the rooms, mechanical brushes, air jet brushes or air snakes knock the dust loose inside the ducts.

Another excellent method uses a smaller vacuum unit located inside your house near the furnace. It should have a HEPA exhaust filter so the dust from the ducts does not get into the room air. A third method uses a rotating brush attached to a vacuum nozzle. The brush-nozzle is run through the ducts.

When it comes to duct cleaning, don’t just shop for price. There are actual differences in the quality of the work performed. A poor duct cleaning job can actually be worse than none at all because it stirs up the dust in the ducts. Look for companies with National Air Duct Cleaners Association certification.

Before you sign the contract, ask for visual evidence the ducts need to be cleaned. Ask the contractor how he plans to clean the other key components (heat exchangers, coils, pans, etc.) If one component is left uncleaned, it may recontaminate the entire system. Ask for a full-duct-length visual inspection after the job is done, preferably with a camera in the ducts.

Write for (instantly download – www.dulley.com) Update Bulletin No. 733 – list of 550 certified duct cleaning companies across the country, descriptions of various cleaning methods and a checklist for selecting a duct cleaning company. Include $3 and a business-size SASE, and send to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.