To clean or not to clean! That is the not question? With regard to cleaning or not cleaning air movement systems, it should not be a question at all. The real question should be “What technique is being used to clean the air movement system?” Ads that propose to clean ducts of an entire house for “$39.95” or “$69.95” or “$99.95” or some such low price, signal abuse to the degree that it could reasonably be called fraud. The fact is, to properly clean ventilation systems, including air ducts, requires a certain amount of time, labor, expertise and equipment. So proper cleaning can be relatively costly, but doing it right is absolutely crucial!
Just because you have filtration, even good filtration on HVAC (Heating, Ventilation and Air Conditioning) systems does not prevent the interior from accumulating particulate matter (dust/debris). Even high quality filters will allow some small particulate matter through including particulate from the filters themselves. This can account for substantial accumulation after a number of years. Consider problems like air bypassing filters, missing or deteriorated seals or gaskets, breaks, disconnections or other leaks inside ducts. These and other conditions result in dust accumulating inside ventilation systems. In cooling mode, air flowing through coils causes condensation. This water must be channeled properly or microbial growth inside the HVAC system can result. Improper design or operation of the condensate water drain system can cause leaks or flooding inside. Accumulated organic matter becomes a food source for molds and bacteria.
Dust is not just dirt. Dust is an accumulation of a wide variety of materials including potentially irritating, toxic or allergenic particulate. Usually the major component of dust inside a building is flaked off skin, or dander. This is organic material that with added moisture is food for mold and other microbes.
Dirty cooling coils that become clogged with particulate matter will cause air to rush at greater speed in those portions that are not clogged. This results in water droplets being blown off the coil, combining with organic matter to produce mold growth in the air handler beyond the coil and potentially in supply ducts.
Fiberglass insulation inside air handlers and ducts will eventually become torn or deteriorated, resulting in fibers collecting in the air pathway and eventually blowing out into the occupied space, potentially affecting occupants.
Failure to clean HVAC systems correctly and completely has stoked the fire of controversy. It was because of abuses in this field that the National Air Duct Cleaners Association (NADCA) was formed and guidelines established for proper cleaning.
NADCA has stated: “Research by the U.S. EPA (Environmental Protection Agency) has demonstrated that HVAC system cleaning may allow systems to run more efficiently by removing debris from sensitive mechanical components. Clean, efficient systems are less likely to break down, have a longer life span, and generally operate more efficiently than dirty systems.”
The EPA writes, “If not properly installed, maintained and operated, these components (heating, ventilating and air-conditioning components) may become contaminated with particulates of dust, pollen, or other debris… Failure to clean a component of a contaminated system can result in re-contamination of the entire system, thus negating any potential benefits.”
It seems clear that cleaning of air movement systems is a correct action if done properly. There are many ways, unfortunately, to clean these systems poorly.
How about inserting the hose of a shop vacuum into a ventilation supply register and turning the vacuum on? This is the method used by what are referred to in the industry as "blow and go” duct cleaners. Companies that advertise cleaning of entire systems for $69.95 or a similar price, generally use this method. Common sense would dictate doubt in the effectiveness of such a method.
Fogging the interior of the ducts with a biocide containing encapsulating material, either in conjunction with or instead of the shop vacuum method is another technique I would label improper. According to the EPA, biocides can have a worse effect on occupants than microbes. These encapsulants do not cover the interior thoroughly, but tend to puddle at the bottom. “Coating the dirt” is never a good idea and doing it poorly makes matters worse. In some cases, such as when significant fungal or bacterial contamination has been established as present or was suspected as being present inside ventilation ducts, fogging with an EPA registered sanitizer (not an encapsulant) after source removal could be appropriate.
Sucking dirt and debris out of the ducts using a power vacuum or a negative-air machine that collects the material is another practice sometimes employed. Equipment is hooked up to the ducts to suck out the offending material. There may be some limited applications for this method, but potential damage to ducts is possible due to the suction created. In most cases, a large portion of the dirt inside is caked on and must be agitated to be effectively removed. If not removed, this material can later enter the airstream due to any of a variety of disturbances.
Some duct configurations might be suitably cleaned using the above mentioned equipment along with compressed air to help loosen and direct the debris. A “skipper” or “whip” or a rotating brush can be used to loosen caked on dirt. Variations of this equipment can be effective, especially for small, inaccessible metal ducts that are in good condition. Properly sized equipment is essential in such operations.
None of the above methods are fully effective in cleaning dampers, turning vanes or duct-joint seams.
To clean ducts completely, you often have to get dirty! Hand brushing and HEPA vacuuming at least part of the duct interiors is needed to clean most duct systems fully. Access ports are cut into ducts to permit a serviceman to brush and vacuum interior surfaces including turning vanes, seams, etc. Joints or access ports must be properly closed and sealed after cleaning.
Pressure washing coils plus repair or replacement of fiberglass liner in air handlers and ducts plus sanitizing the coils using an EPA registered sanitizer should be done along with duct branch cleaning. Replacing deteriorated or microbially contaminated insulation with a non-fiberglass liner is also recommended.
The bottom line on cleaning of HVAC systems is that often a combination of methods might be needed. The techniques should be determined by what is suitable to the particular system or situation as judged by a properly trained and experienced technician. Just because you know how to sweep a floor doesn’t mean you can now claim to be a duct-cleaning professional. This, I submit, is the basis of the controversy.
How often ventilation systems should be cleaned depends largely on the type of environment in which the system exists, the efficiency of seals, gaskets and filtration plus the quality of maintenance. Cleaning air handlers, particularly coils should be done once a year. Ducts should be cleaned about every five to ten years. A specific time line for cleaning any part of HVAC systems should not supercede visual inspections that can better determine the necessity for cleaning. Anyone who has doubts if a system needs cleaning should simply contact NADCA for guidelines and either look for himself or get a NADCA Certified HVAC Inspector to look for you.
I see no valid reason to question the need for cleaning ventilation systems. Underpinning this dispute is the lack of knowledge of methods for proper and complete cleaning of the various duct materials and configurations. There is no doubt in my mind that dirty HVAC systems will lower the quality of indoor air. It follows that proper and complete cleaning of dirty HVAC systems will improve indoor air quality of the space served. I believe that this conclusion works logically and empirically. Readers are, therefore, invited to test the supposition on their own and perhaps put an end to this dispute once and for all.