Should chemical biocides be applied to the inside of air ducts?

Sometimes the recurrence of dust in the ducts cannot be stopped just by cleaning them with brushes and HEPA vacuumcleaners. The duct cleaner will suggest you to go for chemical treatments which includes using biocides or sealants. The biocides are said to be effective for stopping microbial growth in the ducts. Thesealants cover the inside surfaces of the air ducts and equipment housings to prevent the discharge of dirt particles or fibres from them. Generally, these procedures are applied only after proper cleaning and replacements of wet and moldy sections.

You should know that none of thechemicalsfor use in duct boards madeof fiberglass or ducts havingfiberglass lining are registered with EPA (Environmental Protection Agency). There are a few products registered with EPA for using them inside bare sheet metal air ducts. Some air duct cleanermay askyou to get your ducts sprayed with ozone to kill biological contaminants. Ozone is a very reactive compound, whoselevelin the outside air is regulated as it can cause irritation of the lungs.

Both the NADCA (National Air Duct Cleaners Association) and EPA do not recommend the use of antimicrobial chemicals in the air ducts. Awarenessagainst these is being raised among homeowner by highlighting potentialhealth hazards they can generate. They NADCA member who sells such stuff are also beingwarned of the potential legal liabilities they would face by providing them.

The chemical biocides are regulated by EPA under Federal law. All chemical products must be registered with EPA to apply for a respective purpose. The specific use(s) of a chemical will be present on its label. It is a violation of the law, not to use it in consistence with instruction given on thelabel.

Consequences of using biocide and ozone application in air ducts:

• Although not much is known about the possiblehealthhazardsthat can be caused by these chemicals, introducing them into your duct may lead to their discharge into various areas of your house.

• Many people could encounter adverse health conditions due to them.

However, if you must use them in your ducts, follow the following measures to be on safe side:

• Ask your cleaner to showproper evidence of microbial growth in your duct work. Remember, confirming dark patches on the duct as mold requires a laboratory test. Even expert cleaners cannot determine them with naked eyes.

• If they are present, ask them whyphysical ways like dusting nad brushing cannot remove them.

• Take a look at the label on the biocide and check its range of use and possible side-effects.

• The biocideshould only be used in the un-insulated areas of the duct system after proper cleaning.

• Use the productaccordingto the instruction. Low toxic products can be used with members present in the house. Nevertheless, it is always better to leave the premises when they are being used.

In case you or any member of the house suffers uneasiness after spraying them, then open doors and windows to let fresh air flow in from outside. Run the fan of the HVAC system. Leave the premises if necessary. Consult anIndustrial Hygienist to discuss the problem.

Are sealants really effective in controlling the discharge of dust particles in the air?

Sometimes the ducts with fiberglass lining are damaged beyond repair. In such cases it is always feasible to get it replaced. But whenthe damage is notthat severe, it can be recovered by using sealants on it. Encapsulation is the process of using sealants to re-cover the fiberglass lining of the air ducts.When the fiberglass liner becomes loose, its particles can travel with the air that passes through the duct and enteryour living quarter. Fiberglass in the air can cause respiratorytroubles. .

Besides repairing fiberglass linersealants, as claimed bytheir manufacturers,prevent dust and dirt particles inside air ducts from being released into the air. Sealants are applied by sprayingthemin your ducts. Experts opine that through this process, the whole surface do not get coated well and uniformly. Application of sealants may also affect the acoustical and fire retarding characteristics of fiber glass. Not much is known about the safety and effectiveness of these products. The influence of their toxicity in day to day use and in situations of arson is not knownwell.


Various organizations associated with duct cleaning, including EPA, NADCA, NAIMA and the Sheet Metal and Air Conditioning Contractors' National Association (SMACNA) do not endorse the routine use of sealants to encapsulate contaminants in any type of duct. Sealants are absolute no-no on wet duct liner to cover molds and debris. They should be applied only after thorough cleaning and following the NADCA guidelines.

How to know that the duct requires a professionalcleaning?


AlthoughNADCA recommendscleaning of your ducts once in three or five year, you should look for signs of dirt and dust inside to decide for a professionalcleaning. It is okay to have a little dust in your vents. But if they are heavily lodged with dirt go for a professional cleaning. The vents, motors and coils accumulate lots of dust which also contains flakes of dead skin, hair, and pet dander. All thesetogether generate a mat-like layer where bacteria, mould, dust mites, and allergens can flourish. Here are some indicators of a thickly dust-laden HVAC unit.


• Watch out for small wisps of dust coming out of the ducts whenever you turn the HVAC unit on.

• Open one of your vent covers and look inside. See if there is a matted-dust, debris or pet hair trapped in it.

• Look for a thick and fuzzy coating of dust in the grill on the return air registers.

• Take out the air filter. See if it is clogged with dust. If so, the air flow is getting restricted. Unless the filter is cleaned, more dust will settle in the return ductwork.

• Take a look at the furnace compartment by opening it. Check out the blower fan and motor for signs of dust as well as the furnace controls.

Also examine the air conditioning coil. If it is too dusty then it will not allow the filters to work properly.

• You should always be conscious of musty odor in the house which could be an indicator of active mold growth in the ducts. A strange discoloration on the vents may as well be an indicator of molds.

What are the pros and cons of duct cleaning?

Pros of duct cleaning


Apparently, duct cleaning does have some benefit. Let’s take a quick look:

• Duct cleaning boosts the efficiency of HVAC system. Dirt and dust decreases the efficiency of a HVAC system. In the winter season, the dust-laden heat exchanger fails to warm up the air efficiently. In the summer season the dirty condensing coils are unable to cool properly. They work harder to produce desiredoutcome. It increases the HVAC system’s run time, requiring it to exhaust more fuel and energy.


• Duct cleaning ensures a better flow of air. Dirt and dust restrict air flow. If your blower and motor cannot turn smoothly then they are unable to circulate that warmed or cooled air throughout your home.


• Duct cleaning increases the longevity of your HVAC unit. A dirt-lodged HVAC system will run longer to produce the desired outcome. It will suffer more wear and tear consequently. The AC compressors, hydro pumps, burners, and motor bearings will begin to wear out soon.


• Besides fine dirt, dust also consists of dead skin, pet dander,and microorganisms from cat litter, pollen, mold spores, fungi, and even rodent feces. If uncleaned, they will multiplyand infest the whole house. No matter how diligently you clean your house, it is difficult to remove fine particulate contaminates just by dusting.

The cons of duct cleaning:

• According to the EPA there is no scientific evidence that duct cleaning can prevent health problems.

• The dust particles inside your house do not necessarily emanate from ducts. There is no research confirming that particulate contaminants in air increases due to dirty ducts. The particles in the ducts mostly stick to its surface. Dirt in the house comes from various indoor and outdoor activities like smoking, cooking or cleaning.

• There is also no concrete proof thatratifies that cleaning ducts and components of the HVAC unit will make the furnace or the coolerfunction better.

• Cleaning ducts is also a costly affair. It would cost between $400 to $1,000, depending on the extent of the cleaning and the size of the home.


• Cleaning the duct is a time-consuming job that will make the entire house dirty. Loosening the dust and mold in the duct can spread them throughoutthe house readily.

• Some cleaning services will suggest applying chemical biocides to treat the duct surfaces infested with microbiological contaminants. But consequences of these chemicals on health are still not known.



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