February 2011 Energy Solutions

by James Dulley
Engineering Consultant

Have ductwork inspected as part of having your system cleaned

Q: When my furnace was serviced, the technician asked if I have had my ducts cleaned. I am concerned about my family’s health and clean indoor air. How can I tell if they need to be cleaned, and how do I select a company?

A: Healthy indoor air should be a goal for any family. This is particularly true in today’s more energy efficient, airtight houses where the air quality is often worse than outdoor air. In addition to some dust from the ducts, there are many sources of indoor pollutants, including cleaning, cooking, and outgassing synthetic materials. Many of these can be removed from indoor air with a combination of whole-house, furnace-mounted air cleaners and smaller individual room air cleaners.

According to the U.S. Environmental Protection Agency, much of the dust in heating and air-conditioning ducts tends to adhere to the duct surface, and it never gets into the indoor air circulating throughout the house. Just because you see some dust collecting on the grill over air registers does not necessarily mean the ducts are very dirty and need to be cleaned.

Other than just a benign, fine layer of household dust inside of the ducts, there can be some potentially harmful particles inside them. Especially in humid areas, mold spores inside the ducts can cause serious allergic reactions in some people.

Bacteria can also live in some ducts under certain conditions. Very fine particles, from cigarettes or wood-burning fireplaces, can become airborne and cause respiratory problems. Test kits are available to take a sample of the dust from inside the ducts and have the sample tested for mold and other potentially harmful contaminants.

Although it is commonly referred to as “duct cleaning,” if you choose to have it done, it is important to have the entire HVAC (heating, ventilation, air-conditioning) system cleaned. This includes the furnace and air-conditioner blower, heat exchanger/coils, and drain pans in addition to the ductwork. Air conditioner evaporator coils can collect a lot of dirt because they get damp when the unit is running, and dust in the air sticks to the wet surfaces. This reduces the energy efficiency of the entire system.

If the contractor who services your HVAC system also does duct cleaning, you may get a discount by having the service and cleaning done at the same time. The typical cost for a complete cleaning ranges from about $500 to $1,000, depending on the size of your home and the complexity of the duct system.

You might want to have the duct system inspected before going to the full expense of a cleaning. Look for a company that will deduct the inspection cost from the total project cost should you choose to have it cleaned. Technicians conduct the inspection by looking into ducts and the furnace blower unit and using mirrors at bends. They can also move a mini-television camera through the ducts. The inspection should also determine if there are leaks in the ductwork needing to be sealed and/or obstructions to be removed that keep all the conditioned air you’ve paid to have heated or cooled from reaching its intended destination.

When selecting a duct-cleaning company, there are several factors to consider. As with any project, the reputation of the company is highly important. Although the ducts can be inspected afterward to see how well they have been cleaned, your best assurance is to start with a reliable contractor. Always check references with their past customers.

The National Air Duct Cleaning Association is the trade group that certifies HVAC system cleaning contractors. The certification is legitimate and requires extensive training. For a company to be certified, it must have a Certified Specialist on staff. Find a national listing of certified companies, along with its number of specialists, at www.nadca.com.

Also, when selecting a contractor, ask about the type of cleaning equipment each uses. If an indoor vacuum unit is used, it must have a high efficiency particulate arrestance (HEPA) filter on the exhaust to trap all the particles. Some of the particles they dislodge from the duct walls can be very fine, and a lesser quality filter will not remove them from the exhaust air.

Another option is an outdoor truck with a built-in vacuum unit and a long hose. Because it is located outdoors, the exhaust filter is not critical. These large vacuums are very powerful to overcome the air flow resistance in the long hose. The only problem is during winter they suck quite a bit of the heated air out of your house during the cleaning process.

Some duct-cleaning companies may suggest spraying a chemical biocide inside the ducts to kill mold and bacteria and to keep them from growing in the future. If you do have this procedure done, make sure they use EPA-approved chemicals designated for sheet metal ducts.


James Dulley is a nationally syndicated engineering consultant based in Cincinnati.

If you have a question about energy use or energy-efficient products, send it to: James Dulley, Electric Consumer, 6906 Royalgreen Drive, Cincinnati, OH 45244; or visit www.dulley.com.