Chemical biocides are regulated by EPA under Federal pesticide law. A product must be registered by EPA for a specific use before it can be legally used for that purpose. The specific use(s) must appear on the pesticide (e.g., biocide) label, along with other important information. It is a violation of federal law to use a pesticide product in any manner inconsistent with the label directions.
The amount of time air duct cleaning takes can depend on how extensive your duct system is, how old your air ducts are, and whether they have ever been cleaned. On average, expect a standard size home (between 2,000 and 3,000 square feet) to take 2-5 hours for one to two technicians to clean. Here are the proper protocol and equipment you should expect from a professional duct cleaning service, as recommended by the Environmental Protection Agency:

Had our ducts cleaned late April, 2016. Sodium Chlorite was sprayed into ducts after cleaning. Ever since, we have been bothered with eye and nasal passage irritation because of a “chemical” and “musty” odor. This odor is present whether or not a/c is on.) We are told the sodium chlorite (“EnviroCon, manufactured by Bio-Cide International) is used in hospital and nursing home settings and is not hazardous to health. The air duct company’s suggestion is that they come out and spray even more sodium chlorite…we absolutely don’t want this done! Have had various other recommendations about what we need to have done to remedy our problem. We will be unable to stay in our home if a resolution cannot be found. We’d be willing to replace the ductwork if necessary. (One professional suggested that the cleaning may have “knocked something loose” inside the ductwork and that is the source of the irritant.) This home was built in 1920…no idea when the present ductwork was installed. Any suggestions would be appreciated.
The amount of time air duct cleaning takes can depend on how extensive your duct system is, how old your air ducts are, and whether they have ever been cleaned. On average, expect a standard size home (between 2,000 and 3,000 square feet) to take 2-5 hours for one to two technicians to clean. Here are the proper protocol and equipment you should expect from a professional duct cleaning service, as recommended by the Environmental Protection Agency:
Had our ducts cleaned late April, 2016. Sodium Chlorite was sprayed into ducts after cleaning. Ever since, we have been bothered with eye and nasal passage irritation because of a “chemical” and “musty” odor. This odor is present whether or not a/c is on.) We are told the sodium chlorite (“EnviroCon, manufactured by Bio-Cide International) is used in hospital and nursing home settings and is not hazardous to health. The air duct company’s suggestion is that they come out and spray even more sodium chlorite…we absolutely don’t want this done! Have had various other recommendations about what we need to have done to remedy our problem. We will be unable to stay in our home if a resolution cannot be found. We’d be willing to replace the ductwork if necessary. (One professional suggested that the cleaning may have “knocked something loose” inside the ductwork and that is the source of the irritant.) This home was built in 1920…no idea when the present ductwork was installed. Any suggestions would be appreciated.
I moved into a house built in 2003 last year, and spent a lot of time researching air filters because I realize air pollution inside the house is many times higher than outside, and my health and the health of children and youngers can be so adversely impacted by inhaling these indoor pollutants.  I spent a lot of money on the best filters because here in northern Kentucky, I discovered I am allergic to something in the air starting in Spring that made me sick for 10 days - sort of a Upper Respiratory Illness.  It never occurred to me the previous owner had never cleaned the air ducts, although he had both very young children, two dogs and a cat.
And if you have flex duct and/or fiberglass ductboard in your home- the last thing you want is a big brush or anything abrasive running through it. Even high-pressure air can erode ductboard so I wouldn’t clean it with anything. If it becomes contaminated, get rid of it and install real ductwork. If your ductwork is accessible in the basement – the best thing to do is take it down and manually clean it if it’s full of junk. It’s not going to cost a nickel more to do that than to pay $500-1000 for a ‘duct cleaning machine” AKA big blower and vacuum – to do the job.

If you suspect a mold problem — either because of visible growth or a musty smell consistently coming from supply vents — cleaning ducts won’t do much good if it doesn’t eliminate the mold. Mold begins with a moisture problem, and the ducts themselves are unlikely to be the source. The most likely culprits are the cooling system’s evaporator coils, which your heating and air-conditioning contractor — and most duct-cleaning companies — can inspect and maintain. Leaky return ducts can also introduce moisture. Again, if you suspect a mold problem, consider having a service company inspect the duct system for leaks.
I’m really not convinced that duct cleaning is of any value. My roommate wanted the ducts cleaned so he called some company. My scam senses is already tingling. They came in with a big negative pressure fan. Did some blowing and sucking in different vents. Then they tried to upsell a full system cleaning. They wanted to pull the blower and clean the heat transfer box at $700 per heater unit. I have a big house so we have two units. They also tried to sell us some “custom” $250.00 Air Lifetime air filters. At that point I pulled the BS get the hell out bell. After paying $520.00 for just the cleaning, I paid the bill and sent them on their way. I replaced the existing filter with the good old and cheap paper filters at $10.00 each. Duct cleaning… I’m not Impressed.
If you’re concerned about dust, allergens or mold, it may be time to have your air ducts cleaned. The national average cost for air duct cleaning ranges from $190 to $250. Air duct cleaning costs will vary based on a number of factors such as your location in the country, the age and condition of your air ducts, the number of linear feet to be cleaned, and any repairs your ducts may need. HVAC cleaning companies should clearly outline what is included in their services and at what rate, so always make sure you understand and have a written agreement before work begins. Here are some examples of average air duct cleaning costs:
The bottom line is: no one knows. There are examples of ducts that have become badly contaminated with a variety of materials that may pose risks to your health. The duct system can serve as a means to distribute these contaminants throughout a home. In these cases, duct cleaning may make sense. However, a light amount of household dust in your air ducts is normal. Duct cleaning is not considered to be a necessary part of yearly maintenance of your heating and cooling system, which consists of regular cleaning of drain pans and heating and cooling coils, regular filter changes and yearly inspections of heating equipment. Research continues in an effort to evaluate the potential benefits of air duct cleaning.
Duct cleaning generally refers to the cleaning of various heating and cooling system components of forced air systems, including the supply and return air ducts and registers, grilles and diffusers, heat exchangers heating and cooling coils, condensate drain pans (drip pans), fan motor and fan housing, and the air handling unit housing (See diagram).
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