One of the most common questions in my classes is, “What are your thoughts on air duct cleaning?” I now have an up-to-date resource to share with students.
This month’s Indoor Air Journal has an excellent article on duct cleaning titled, “Is ventilation duct cleaning useful? A review of the scientific evidence.” The author of the article is M.S. Zuraimi from the National Research Council Canada.
Debate has always swirled around air duct cleaning. Many professional engineers speak of it being a waste of money. Many air duct cleaners espouse its benefits on occupant health and equipment efficiency. I think the best place to start is to describe how dust and debris build up in the first place.
Return ductwork takes air from the space and delivers it back to the air handling unit. Particles from activities such as cooking or photocopying can get deposited in the return ductwork. Filters may be placed on the return grilles to reduce the deposition of particles in the return duct, but the most common location for filtration is directly before the cooling or heating coils.
Particles entering into a return (or from outdoor air intakes) have a few potential final destinations:
- They can get deposited in the ductwork
- They can be filtered out
- They can move through the HVAC system without being removed
Larger particles or those that accumulate will fall out of the airstream and settle onto the duct surface. Smaller particles are more likely to be filtered out. The smallest particles will likely move through the entire system without be removed at all.
The journal article analyzed peer-reviewed literature from 1980 to 2009. After removing a few articles that did not meet pre-set criteria, they were left with 48 articles to review. As with most literature reviews, the findings were a mixed bag of results.
Here is the final conclusion of the article, “this scientific review concludes that there is poor evidence that [duct cleaning] can improve or provide good IAQ.” The article found that although duct cleaning was often efficient in removing dust and debris, it wasn’t conclusively effective in improving the IAQ. In fact, some studies showed that disturbing the dust during cleaning resulted in a degradation of indoor air quality.
Anyone interested in the topic of air duct cleaning should purchase this article and obtain two other resources (both free):
- Should You Have the Air Ducts in Your Home Cleaned? by the EPA
- Assessment, Cleaning and Restoration of HVAC Systems (PDF download) by the National Air Duct Cleaner Association (NADCA)
These two resources take differing views on the topic of duct cleaning so I strongly recommend reading both.