If you have a home with a forced air heating and/or cooling system, the condition of your ductwork may be a concern to you. It seems like at the beginning of every heating and cooling season, the snake-oil salespeople crawl out of the ductwork and attempt to sell their services by making all kinds of claims as to why you should have your ducts cleaned.
Before you go buying any oil, let’s look at the facts around duct cleaning. It is usually not going to be too helpful to ask duct cleaning companies for the best information as they are likely to be biased. We must look to other sources for the best information.
Let’s start with a basic question and then see if we can answer that question.
Why do You Want to Clean Your Ducts?
Here are a few answers:
1. My home inspector told me I should get them cleaned.
2. To improve indoor air quality.
3. Because they are REALLY dirty.
4. Because it will cure my kid’s allergies.
5. The TV said I have to do it, so it must be true.
While all of these may sound like “good” reasons, they might not actually be good advice, true advice, or help accomplish what is claimed.
Note: Before I go into typical duct systems in the average home, if you have had temperature differentials or flooding conditions that have actually allowed for the ducts to become contaminated with microbial growth, then by all means have them cleaned in conjunction with fixing the moisture issue. This would likely involve replacement of the ducts however – not cleaning of the ducts. Also, I am not talking about ductwork that has been impacted with known pollutants or carcinogens. Your average duct cleaning company is not going to be qualified to evaluate these concerns either.
Ductwork Acts as a Filter
For all of you with “normal” ductwork installations, think of your ductwork as a very long filter.
As air moves through the ductwork, over time the heavier dust particles fall out of the airstream and stay in the duct. As more time goes by, more dirt falls out of the airstream and continues to build up in the ductwork. The dust building up in the duct causes the air to actually become a little more turbulent which results in even more dirt falling out of the airstream. Essentially, the cleaner and/or newer your ductwork is, the less “filtering” that goes on.
Your ductwork does not “grow dust” to send into the airstream – it actually cleans the airstream in most cases.
Cleaning ducts “prophylactically” to fix a health concern may not alleviate the health concern at all and may make the indoor air quality worse. So, when health concerns are an issue, the actual cause of the health concern must be determined – it may not be the ductwork at all; it is likely not the ductwork at all.
As more and more people become concerned and interested in indoor air quality, it is only logical that we would think about our dirty ductwork. It is easy to assume that this crud is being blown into our homes and somehow contributing to poor indoor air quality. Actually, the opposite happens, and there is no hard scientific evidence to support that duct cleaning prevents health problems. Even the EPA agrees and does not recommend “routine” cleaning of ductwork.
If and when you have your ducts cleaned, proper precautions must be taken to protect the workers doing the cleaning, as well as protecting the occupants of the home. It will also be necessary to protect the home itself from “contamination” with HEPA filters, etc.
Consider Other Sources of Poor Indoor Air Quality
There are many other sources of poor indoor air quality that can and should be considered before picking on ductwork as a contributing cause of health concerns. Things like smoking, wood burning appliances, gas appliances, furniture, pets, dust mites, vacuuming carpets, household cleaners, VOCs, open windows, closed windows, inadequate ventilation, proximity to industry, proximity to roadways, even cooking, and a gazillion other things should be looked at first.
Before cleaning your ductwork, consider a couple of things. First, your ducts will do less filtering of the air after cleaning, and any remaining dust in the ductwork may find its way into the airstream and end up inside your home. An efficient and well maintained filtering system installed in this airstream is critical to keeping any dust that does not get filtered by the ductwork from finding its way into your home.
What constitutes a proper filtering system could be the topic of another post – it is much more complicated than running down to your nearest big box store and buying the type of cheap, throw-away filter that is present in many furnaces.
For more detailed information about the science behind the fallacy of the need for duct cleaning, please read “Duct Cleaning for Quackers?” by Forensic Industrial Hygienist, Caoimhin P. Connell.
Written by Charles Buell, Real Estate Inspections in Seattle