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Duct Cleaning: Understanding More About This HVAC Service

Published on: December 4, 2013

Like many optional home service procedures, there’s a time and place for duct cleaning. Not every home is a good candidate, and certainly not every HVAC or air quality problem is a result of dirty ductwork. However, certain common conditions prevail in most residences. One central fact is that whatever is floating around in your breathing air tends to accumulate in your ductwork and vice versa. Homeowners who suspect that unhealthy conditions exist in either the indoor environment or the inside of ductwork may benefit from the services of a professional duct inspection to verify or rule out contamination. Where the need for professional duct cleaning is clearly established, it can be a beneficial part of an overall strategy to enhance indoor air quality.

Suspects and Symptoms

Common allergens such as inorganic household dirt, dust and lint stirred up by normal activity are often inducted into the HVAC system through return vents. While some of these particulates are captured by the system air filter, large amounts attach to ductwork surfaces by static cling, coating the insides of ducts and providing an ongoing source of air contamination. A continuous exchange may develop as ducts both accumulate and release particulates into the interior environment whenever the HVAC fan is running.

Mold spores released from mold colonies growing in the home are a verified source of allergic reactions in susceptible individuals. These invisible, living airborne particulates are buoyant and often get continuously circulated throughout living spaces, conveyed by the flow of conditioned air through the home’s ductwork. The design and construction of HVAC ductwork can seem like the blueprint for a mold colony: Dark passageways continuously supplied with airflow containing circulating spores and organic particulates that serve as mold food. During summer, the A/C evaporator coil condenses large amounts of water out of the air, providing the wet surfaces and drain pan that also act as a magnet for mold growth.

Symptoms of continued exposure to airborne allergens include:

  • Coughing and wheezing.
  • Runny nose and sneezing.
  • Respiratory congestion.
  • Irritated and watery eyes.
  • Asthma attacks.
  • Generalized fatigue.

Before attributing any physical symptoms to dirty ductwork, always discuss them with your doctor first. Other evidence that duct cleaning may be in order includes daily housekeeping issues such as excessive dust on surfaces in the home, frequent air filter clogging, obstructed A/C coils, and even shortened service life of components installed in the duct air stream such as the blower fan.

To Clean or Not to Clean

Since any or all of the above problems may have origins other than dirty or contaminated ducts, duct cleaning is not necessarily indicated or effective in all cases. However, the U.S. Environmental Protection Agency has issued guidelines for homeowners considering a duct cleaning procedure. Here are some simple questions to help you make an informed decision about duct cleaning:

Is actively growing mold observable on the interior duct surfaces or components like the evaporator coil? It’s hard to tell just by looking, and many mold-like accumulations aren’t really mold. A professional inspector will take samples of suspect mold as well as test the airflow in the ducts to determine the presence of active living spores.

Are the ducts infested with rodents or other vermin? Rats, mice and other unwelcome guests use the dark enclosed spaces of ductwork as breeding grounds. They also leave droppings and frequently die and decompose inside ducts, as well. Any evidence of rodent infestation should be considered a red flag.

Have the ducts been inundated with water? Roof leaks, plumbing leaks or even unusually excessive humidity from sources such as a flooded basement can contaminate ductwork with moisture and create a likely environment for mold or bacterial growth.

Can you visually observe dust, dirt or other airborne substances emitted from duct vents when the HVAC fan is running?

Are you experiencing energy-efficiency issues with your heating and cooling system that cannot be explained by other common causes such as duct leakage, an improperly sized furnace or A/C, or inadequate maintenance? Dirty ducts raise the internal air friction inside the system and cause the blower fan to work harder and the burner or compressor to run longer cycles.

If the evidence suggests that your ducts are suspect, a professional inspection by an HVAC contractor is the best next course of action. An inspector will access areas of the ductwork generally not visible to homeowners and use mirrors, right-angle periscopes and micro-video cameras to visually survey the entire span. Samples of suspect organic growth can be taken and other possible explanations for dirty ducts, such as air leakage due to deteriorated joints and seals can also be assessed.

Here are some guidelines for selecting a competent professional to inspect and, if necessary, clean the ducts.

  • Choose a reputable local contractor with an established track record in the community. The company that sold and installed your existing heating and cooling system is a good place to start making inquiries.
  • Ask for local references and check them. Find out if previous customers were satisfied with the result.
  • Ask if the contractor is a member of NADCA, the National Air Duct Cleaners Association. This non-profit industry organization establishes professional standards for duct cleaning, and provides training, education and certification to member contractors.
  • If the prospective company makes extravagant claims about the health benefits of duct cleaning or other unrealistic promises, consider another contractor.
  • Ask about the use of biocides and other sanitizing chemicals. Make sure the contractor uses EPA-approved substances and is knowledgeable in safe application.
  • Find out whether your state requires duct cleaners to be licensed, then verify that the contractor’s license is valid.

A Typical Procedure

While the ductwork differs in residences according to the size and configuration of the floor plan, duct cleaning follows a general procedure common to most homes. The procedure comprises three stages:

Access: Comprehensive duct cleaning requires access to the entire span of ductwork. The contractor will remove access plates and open other convenient access routes by removing diffusers, elbow joints and manifolds. In places where no removable access is available, small holes may be cut in the ductwork to allow insertion of cleaning tools. These holes will be professionally closed and sealed after the procedure.

Agitation: Layers of dirt and dust often adhere to the interior duct surfaces. This buildup usually has been accumulating for years and must be physically dislodged so it can be removed by the subsequent vacuuming phase. A professional duct cleaner will utilize tools including hand brushes, powered brushes, blowguns and various air-driven agitators to break down the accumulation.

Removal: In order to prevent any contamination of the interior of the home, the entire duct system will be placed under negative pressure with a powerful vacuum as loosened contaminants are removed through the access points. All material is drawn into bags that are tightly sealed and removed from the premises for proper disposal. The vacuum exhaust typically incorporates a HEPA-grade filter to prevent infiltration of even microscopic particles into the home.

Where the presence of mold or other microbial growth is verified on non-porous duct surfaces only, approved biocides may be applied. NADCA standards also specify that any duct cleaning procedure include cleaning ancillary equipment installed in the duct airflow, including the air conditioner coil, blower fan and furnace components.

Following the cleaning procedure, all removed duct components will be reconnected and access plates installed. Holes cut to gain access will be covered and sealed. A new filter will be installed and, after the system is restarted, proper airflow and air balance verified in every room.

Have more questions about duct cleaning? Contact us to find a contractor in your area of the Southeast United States.