I replaced all the ducts but the trunks in my 1969 home when I replaced the horizontal furnace under the house with a gas pack. I got advice from a friend who was an HVAC contractor. I was surprised to find the trunks and other ducts very clean. I replaced the individual runs with flex primarily for the insulation. I wrapped the trunks with insulation also.
Since most states and municipalities don’t license air duct cleaners, you need to check their professional credentials instead, such as NADCA membership. EPA recommends all duct cleaners follow NADCA standards. Member companies must keep at least one technician on staff who has passed a NADCA test. “They have to pass rigorous testing to earn the certificate, and our code of ethics is very important,” Vinick says.
If the system is sealed air-tight and a really good filtering system is in place then you should NEVER have to clean your ductwork. Most dust people see in their homes (on beds furniture etc....) is broken down insulation that is being blown into the home from the attic (venturi effect) where the duct bucket (box etc...) is not sealed at the sheetrock ceiling. On the return side, ANY leaks in the ductwork will pull hot attic air and dust into the system, clogging up everything.
As I type this, I am having my ducts cleaned. About 30 including returns and the furnace. $543.00. I am watching the team do it and can see the clear vacuuming tubing and how dirty it has become. I like the gentleman’s comment on “stick your head in your vacuum and breath”….I get it. The team showed me the machine and it’s filtration system…and they will show me it again after the cleaning. However, like I said before, I am actively seeing the tubing that is clear before they start and how dirty it is once they begin and continue cleaning. Reputable company and not a “fly by night” coupon service. People don’t be so cheap, that is your problem.
A year and a half ago (fall of 2015) we replaced the furnace and air conditioner. From what we could determine this was the third forced air furnace and second air conditioner unit for the house. As part of the installation, we changed out the two 6″ ducts feeding the second floor with 8″ ducts. The idea was to get more cold air to the second floor in the summer. It worked and for the first time the second floor and first floor temperatures were the same when the air conditioner was running. Of course, to make the system work I close down upstairs duct damper doors in the winter and open them up in the summer.

All of the products discussed above are registered solely for the purpose of sanitizing the smooth surfaces of unlined (bare) sheet metal ducts. No products are currently registered as biocides for use on fiber glass duct board or fiber glass lined ducts, so it is important to determine if sections of your system contain these materials before permitting the application of any biocide.
I’m a heating and air conditioning contractor. I’ve been in the trade for over 15 years. I’ve witnessed numerous duct cleaning projects and talked with many duct cleaners. Duct cleaning as it’s usually promoted is a fraud. Most duct cleaners claim to deliver cleaner air. They deliver exactly the opposite. The studies on duct cleaning prove it, including a May 1998 study sponsored by NADCA and the EPA! The stories are compelling, but they can come up with stories that “prove” anything they want. Internet searches are dominated by results from those who are paid to tell you that duct cleaning is worthwhile. Search a little more and you’ll find the truth.
You may consider having your air ducts cleaned simply because it seems logical that air ducts will 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. EPA does not recommend that the air ducts be cleaned routinely, but only as needed. EPA does, however, recommend that if you have a fuel burning furnace, stove or fireplace, they be inspected for proper functioning and serviced before each heating season to protect against carbon monoxide poisoning.
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