Home Inspector’s Guide to Air Duct Cleaning, Part 1: Some Factors to Consider

 by Nick Gromicko, CMI® and Ben Gromicko



Whether or not a home inspector should recommend that their homeowner-clients have the air ducts in their house cleaned is a decision that's based on several important factors, including the Standards of Practice they follow and the scope of the home inspection. According to the InterNACHI Home Inspection Standards of Practice, a home inspector is not required to determine the home's air quality, the presence of airborne hazards (including mold), or the presence of rodents or insects. Determining the need for the air ducts to be cleaned is beyond the scope of a home inspection. InterNACHI encourages home inspectors to read this six-article series in its entirety, as it provides important information on the subject.

Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle or dust levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to the duct's surface and does not necessarily enter the living space. It's important to keep in mind that dirty air ducts are only one of many possible sources of airborne particles present in a home. Pollutants that enter the home both from outdoors and indoor activities, such as cooking, cleaning, smoking, or just moving around, can cause greater exposure to contaminants than dirty air ducts. Moreover, there is no evidence that a light amount of household dust or other particulate matter in air ducts poses any risk to a person’s health.

A home inspector may decide to recommend cleaning the air ducts in a house if:

  • There is substantial visible mold growth inside sheet metal ducts or on other components of the heating and cooling system. There are several important points to understand concerning mold detection in heating and cooling systems, including the following:

    • Many sections of the heating and cooling system may not be readily accessible for a visual inspection, so ask the homeowner to show you any mold they may say exists.

    • A homeowner should be made aware that although a substance may look like mold, a positive determination of whether it actually is mold can be made only by a certified mold inspector and will require laboratory analysis for final confirmation. For a small fee, PRO-LAB® can tell you whether a sample sent to them is mold or simply a substance that resembles mold.

    • If there are insulated air ducts and the insulation is wet or moldy, it cannot be effectively cleaned and should be removed and replaced.

    • If the conditions that caused mold growth in the first place are not corrected, mold growth will recur.

  • Ducts are infested with vermin, such as rodents or insects.

  • Ducts have large amounts of dust and debris and/or particles are released into the home from the supply registers.

If any of the conditions identified above exist, it usually suggests one or more underlying causes. Prior to any cleaning, retrofitting, or replacing of the ducts, the cause(s) must be corrected or the problem will likely recur.

Some research suggests that cleaning heating and cooling system components (such as the cooling coils, fans and heat exchangers) may improve the efficiency of the system, resulting in a longer operating life, as well as some energy and maintenance cost savings. However, little evidence exists that cleaning only the ducts will improve the efficiency of the system.

A home inspector may recommend having the air ducts cleaned simply because it seems logical that air ducts get dirty over time and should be occasionally cleaned. Provided that the cleaning is done properly, no evidence suggests that such cleaning would be detrimental. The U.S. Environmental Protection Agency (EPA) does not recommend that the air ducts be cleaned routinely, but only as needed. The EPA does, however, recommend that if a house has a fuel- burning furnace, stove or fireplace, it should be inspected for proper functioning, and serviced before each heating season to protect against carbon monoxide poisoning.

If a homeowner decides to have the air ducts cleaned, he or she should assess the service provider's competence and reliability.

Air duct cleaning service providers may tell a homeowner that they need to apply chemical biocide to the inside of the ducts as a means to kill bacteria (germs) and fungi (mold), and to prevent future biological growth. They may also propose the application of a "sealant" to prevent dust and dirt particles from being released into the air or to seal air leaks. The homeowner should fully understand the pros and cons of permitting the application of chemical biocides or sealants. While the targeted use of chemical biocides and sealants may be appropriate under specific circumstances, research has not demonstrated their effectiveness in duct cleaning or their potential adverse health effects. No chemical biocides are currently registered by the EPA for use in internally insulated air duct systems.

Whether or not a home inspector recommends to their clients to have the air ducts in their home cleaned, preventing water and dirt from entering the system is the most effective way to prevent contamination and mold growth.