Ask An Expert: Duct Cleaning

Ask an Expert is an occasional feature where we pose a question submitted by readers to our Healthy Home Director Carl Grimes and Healthy Building Scientist Joe Medosch.

Reader Question: My air ducts are about to be cleaned. What should I expect from the process?

The Importance of Duct Cleaning

Duct cleaning is an important part of removing dust and debris from the forced air distribution ducting in homes. The routine maintenance for duct cleaning can vary from 3-4 years to as long as 10-15 years.* While the principles of duct cleaning are relatively simple, there is some important, general information that needs to be understood so that you don’t inadvertently replace one issue with another and can confidently monitor the work performed to ensure that the job is done effectively and successfully.

In general, if performed properly using correct techniques and equipment, duct cleaning should not impact the health of occupants or make a mess of your home either during or after the work is completed. The vacuum source should be configured to create airflow from inside the house to the vents, then through the ducting to the vacuum hose at the blower to ensure dust and debris is kept out of the living spaces and occupants.

Duct Cleaning Standards

Unlike many other procedures in homes, especially regarding mold, there are two excellent industry standards for duct cleaning. One is from the National Air Duct Cleaners Association and the other is from the Air Conditioning Contractors Association.** Professionals performing duct cleaning should comply with  at least one of these standards.

Duct Cleaning Services: Inspection Comes First

The contractor needs to inspect the entire system, identifying where the main blower is, where all the supply vents are located, and where all the return vents are located. Most ducting cleaning companies now have fiber optic cameras to inspect the interior of the entire system of  forced air ducting. This inspection prior to cleaning can help determine:

Requirements for Successful Duct Cleaning

While the specifics will vary somewhat from home to home, the basic requirements for successful duct cleaning are the same:

Specific Issues with Mold in Ducts

If you know or suspect that there is mold in your ducts, there are a few specific and important things to consider.

Mold and bacterial growth are most likely to grow on the air conditioning (AC) coils and the drain pan below it, as this is where the moisture condenses and can remain long enough for mold growth. Both the NADCA and ACCA standards address requirements for physical removal of mold growth from these areas.***

Mold can also grow on the ducting itself and some types of ducting are more susceptible because of how they accumulate dust and moisture. They type of ducting you have will inform whether it can be cleaned or if should be removed and replaced.

Finally, treating mold with chemicals, gases, fog, deodorizers, is NOT a substitute for physical removal. Physical removal can be done either by cleaning smooth non-porous surfaces, or removing rough or porous surfaces.

Any chemical with claims of killing or controlling mold or bacteria is required by Federal law to have an EPA Registration Number and Label per the Federal Insecticide, Fungicide, Rodenticide Act (FIFRA). The official label will specify if the product can be used in forced air ducting and how it can or cannot be applied. Some products can be wiped but not sprayed or fogged, for example.

Refuse to use if the Registration Number and label cannot be produced. Receive written agreement that they will apply per the label’s instructions. If you are chemically intolerant or have other concerns of safety, refuse their use. If for some reason these products are used, they must be applied after cleaning per FIFRA and standard disinfection practices. They are not to be used instead of physical removal.

The same precautions apply to products promoted as “natural,” organic, or otherwise “safe.” Both the active ingredients and inert ingredients may be problematic for you. Personally test all chemical products before authorizing use.

Maintaining your Ducts

Once your ducts are cleaned, make sure to keep them well-maintained by:

Determining duct leakage requires testing with a “duct tester,” a fan that measures the leakage in CFM (cubic feet per min). The ducts should only be sealed with mastic, a putty for ducts, mastic tape or high-temperature foil tape. Duct tape is not permitted for heating or cooling ducts, it dries out and will fail. Once sealed it should be tested to confirm tightness. If you have a gas furnace or hot water tank in the house or garage the contractor should perform a combustion safety test to confirm the units are not back drafting.

Your individual situation may be different. If you have specific questions, please contact us through our Ask an Expert page and we’ll get back to you!

*How often ducts need to be cleaned depends on multiple factors including: outdoor pollutants, leakiness of the house, occupancy (people and pets), and type of air filters.

**National Air Duct Cleaners Association duct cleaning standard has been internationally accepted, used, and generally validated for over 20 years. Air Conditioning Contractors Association> has an ANSI Accredited Standard. ANSI is as close to a regulation as exists while still being voluntary.

***Note: As mentioned previously, if the coils need to be removed for cleaning or replacement, an EPA Certified Technician is required to perform the operation to prevent the escape of the AC coolant into the air.

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