University of Wisconsin - Extension

If you are considering having your heating ducts cleaned, you should know that the U.S. Environmental Protection Agency (EPA) has raised some concerns about the processes and products involved, said John Merrill, University of Wisconsin-Madison/Extension housing specialist.

The EPA is urging businesses that clean heating equipment and duct work to use caution in applying any antimicrobial agents to interior surfaces of duct work and other components of heating and air conditioning systems. The agency is concerned that most of the available products have not been fully tested for this application.

Residential duct cleaning is a relatively new service offered by heating contractors and others, according to Merrill. In marketing the service, contractors often raise the specter of how dirty ducts can become after years of air flowing through them and that it is likely that house mites may be living and mold may be growing in the duct work.

However, routine duct cleaning is not recommended, according to an EPA publication on the subject -- "Should You Have the Air Ducts in Your Home Cleaned." According to the EPA, duct cleaning has never been shown conclusively to prevent health problems nor is the dirt that may be lining the duct likely to come back into the home.

¿One reason people are interested in duct cleaning is because they believe the ducts may have mold or other biological contaminants in them,¿ Merrill said. ¿If mold is the reason you are considering duct cleaning, be sure to have the contractor show you any mold that exists and if you question whether it is mold, have a sample analyzed by a qualified laboratory.¿

Departments of health can often help you find such a laboratory.

¿It is also critical,¿ Merrill said, ¿to remove the cause of the mold growth before cleaning. The cause is usually some source of moisture, either leaks or condensation.¿

A contractor may recommend that you follow the cleaning with an application of a sanitizer or disinfectant to prevent future mold growth. This is the cause of the current EPA concern. While there are many antimicrobial agents registered with EPA for use on hard surfaces such as sheet metal, few are registered for use in heating systems and duct work. Even those that are registered have not had the extensive evaluation that the EPA now believes may be appropriate.

Two concerns exist, according to the EPA's Tracy Lantz. The first is possible acute or long-term health effects. At present there are only a few reported cases where antimicrobial agents sprayed into duct work cause health problems. In these cases, symptoms have included burning eyes, headaches, itchy skin, nausea or sore throats. There are several health related questions related to the application of antimicrobial agents to duct work. Do appropriate instructions for use in duct work accompany the product? How should the antimicrobial agent be applied? Should the ducts be fogged or a coating sprayed on the surfaces? Should occupants be absent during the work and for how long afterward?

A second concern is about the effectiveness of the antimicrobial agents in duct work. In a layer of dirt with embedded microbes, if the agent is sprayed on the surface will it kill the mold or other problem microbes if it doesn't make contact? Will the agent actually reach all the areas where the microbes are living? What is the effect of the frequent movement of air through the system on effectiveness? If the agent does kill mold, for instance, will the casings, which are still an allergen be released into the air in the duct and find their way into the home?

Because of these and related questions the EPA recommends that disinfectants and sanitizers not be applied in heating and duct systems unless the product is registered for this use and includes specific directions for use in heating and ventilation systems.

If you are a considering having your ducts cleaned and the contractor offers to use a disinfectant or sanitizer as part of the cleaning process, ask to see the product container. Make sure that the product meets these EPA recommendations.

The publication "Should You Have the Air Ducts in Your Home Cleaned" is available on the EPA Web site at http://www.epa.gov/iaq/pubs/airduct.html"> http://www.epa.gov/iaq/pubs/airduct.html.