There is a lot of good, general information in the article. As with anything, the homeowner should do their due diligence in getting enough information to make an educated decision. Should duct-work be cleaned? YES! Does it need to be cleaned annually or even every second or third year? Not necessarily. It all depends on a bunch of variables. You're right that a well designed and balanced system will deliver the right amount of air flow, but sometimes conditions outside the home/business, make it a necessity to get the ducts cleaned. As for mold? NO filter is going to address a mold issue. If you have mold, you have a moisture issue that needs to be addressed. Also, in my 38 years of experience in the HVAC and sheet metal industries, washable filters are one of the reasons ducts need to be cleaned. They are no where near efficient in cleaning/filtering the air to the level that they should.
In most modern homes with up-to-date heating and air conditioning systems, filters are changed regularly through the year, so you may not even need to hire a professional. However, keep your eyes open for the accumulation of dust, dirt, dander and mold. If you see it despite regularly changing your filters it could be an indication you need a high-pressure cleaning.

Most people are now aware that indoor air pollution is an issue of growing concern and increased visibility. Many companies are marketing products and services intended to improve the quality of your indoor air. You have probably seen an advertisement, received a coupon in the mail, or been approached directly by a company offering to clean your air ducts as a means of improving your home's indoor air quality. These services typically — but not always — range in cost from $450 to $1,000 per heating and cooling system, depending on:
Simply living in your home creates dust and dirt. Have you ever seen dust floating in the air in your home when the sun shines in?  Dust, dirt, pet dander, mold spores, and allergens get pulled into the air handling system in your home. They build up in the ductwork; some of it gets recirculated back into your home, and some of it can be captured by a good quality air filter. Eventually, enough debris builds up to the point where most of it blows back into your home. Your furnace or air conditioner must run longer to cool or heat your home, which costs you more in utility bills. With a service call from Sears Air Duct Cleaning, you can feel comfortable knowing that the accumulation of dust, dirt, dander, mold, and allergens has been cleaned from your HVAC duct system.
Duct cleaning is a complete scam, I was a “duct cleaning technician” for a whole week before I was fired for not upselling elderly widowed women $2000 extra for “toxic mold remediation” when their ducts were spotless to begin with. The last two days I was employed there I worked as a “helper” alongside a technician thats been with the company 7 years. He scammed every customer on mold and would at times get as much as $2500 extra for treating “toxic mold” in a typical 3 bedroom house in the suburbs. Wait…it gets even better, the “Biocide” the company used was simply a cheap $4.99 per gallon bought at Home Depot air freshener with no anti-microbial properties that was fogged into the HVAC system for 5 minutes, maybe using 1/2 cup of the stuff. In order to provide the customer with evidence of “mold infestation” the technician would be given bogus mold tests that always resulted in “toxic spores present” regardless if you swabbed the actual duct or nothing at all. Not to mention the actual duct cleaning job (typically $400) did basically nothing and the homeowner could’ve done a better job with a shopvac
Pay particular attention to cooling coils, which are designed to remove water from the air and can be a major source of moisture contamination of the system that can lead to mold growth. Make sure the condensate pan drains properly. The presence of substantial standing water and/or debris indicates a problem requiring immediate attention. Check any insulation near cooling coils for wet spots.
I live in Port Orange, FL. I purchased a double wide mobile home and was saddened to learn that the previous owners were HEAVY smokers! They did a good job “hiding” the smoke smell the day we viewed this place. I did not have a home inspection done unfortunately. My question is: can duct cleaning remove the smoke smell from this place. The ceilings have been treated with Kilz and paint. I personally scrubbed down every wall, floor or surface. I also purchased a ODORFREE OZONE machine. It seemed to remove the odor for a short period of time but my friends are again complaining about the “smoke” odor in my home. The Ozone machine was $400 and I’m terribly upset that it didn’t clean the air as was promised.
After major damage to a small addition on our home was damaged in the windstorm in May, the insurer’s preferred vendor sanded drywall without taping off the area. They relied on heat from the furnace to dry the mudding compound. They claimed they shut the furnace off while sanding and regardless of whether they did or not, they never cleaned up the drywall dust before turning the furnace back on. I now have drywall dust everywhere and my husband took photos to verify our concerns. They even sanded right above a cold air return. Vents were never covered either. The same company that created this mess is cleaning my ducts today. They have refused to clean the furnace. Their are health concerns for my almost 85 yr old mother who resides with us. I’ve tried 3 times in the last 7 days to escalate to a manager and they will not return my call. They just keep sending it back down to my adjuster. There are many other issues we’ve encountered since May as well. This is a major insurance company who has the resources to fix this mess but refuse. Please help!
Ok what you said is true but in most cases ducts are in a duct flex format, and knowing that the dust in people's flex duct is just surface dust, any real debris that are in the duct itself will result in very little to no air flow which will keep your unit from performing properly, but if it is true allergy reasons then replacing your duct system is better for overall better air quality, plus if you do pay attention to the warranty on flexible duct is that it only has a 10 year warranty and typically only lasts for 20 years so do your research before having a duct cleaning, and to add one more thing if your duct work is completely metal and you can't see visible insulation then your duct on the inside has insulation inside of it, if you replace that with duct work that is clean metal on the inside and wrapped with insulation on the outside then it will further reduce the air bourne fiberglass and dust.
Duct cleaning is a band aid, like washing you hands is. Under your description, why wash your hands more than once? If it gets cleaned once, it shouldn't get dirty again. Well that is, unless they touch something dirty. Keeping your hands completely clean is virtually impossible. Same as keeping dust out of your home. You clean your ducts and over a 3-5 year span they get dirty again. Also, duct cleaners are not licensed but should be certified by NADCA(National Air Duct Cleaning Association).
Air duct cleaning service providers may tell you that they need to apply a chemical biocide to the inside of your ducts to kill bacteria (germs) and fungi (mold), and prevent future biological growth. Some duct cleaning service providers may propose to introduce ozone to kill biological contaminants. Ozone is a highly reactive gas that is regulated in the outside air as a lung irritant. However, there remains considerable controversy over the necessity and wisdom of introducing chemical biocides or ozone into the duct work.

Vinick calls air duct cleaning an essential part of home maintenance, akin to mopping and vacuuming. "It’s like changing the oil in your car,” he says. “If you don’t change the oil, you’re going to have a problem. When your components are loaded up with debris, the system has to work harder. When you remove that debris, you get energy consumption savings.”
If there is stuff in the ducts, the fact that it’s laying there and not being blown into the rooms is proof positive that it is hurting no-one. The 5-6 exceptions you cite in this article I’ll buy, but only with the caveat that at least some of those could have been avoided by proper protection (during remodeling for example) – and if asbestos/lead/whatever winds up in your ducts- the remodeling contractor should be the one paying to remove it.
Some research suggests that cleaning heating and cooling system components (e.g., cooling coils, fans and heat exchangers) may improve the efficiency of your 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.
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