There are many benefits to insulating HVAC ducts: the delivery of conditioned air is more efficient and cost-effective, energy is conserved, plus occupants of the building experience improved comfort and less noise from duct operation.
To keep these insulated ducts clean and running in top shape, a high efficiency and properly maintained air filtering system is best. A regular maintenance schedule is recommended, assuring safety for building occupants and protection of the HVAC system.
However, sometimes irregular or improper maintenance can lead to an accumulation of dirt, dust or moisture in an HVAC system. This can restrict air flow and cause problems with the indoor air quality. Which leads to the question: how do you properly clean insulated ducts?
It’s a question we get a lot, and thankfully our friends at the North American Insulation Manufacturers Association (NAIMA) have answers. Keep reading for the highlights and check out their detailed document for more information.
Identify the issue
If you’ve decided ducts need to be cleaned, the first important step is to identify what is wrong with the system – in other words, what led to the need for cleaning? It can be pointless to clean a duct if the underlying issues are still present, as the duct will just get dirty again.
One example could be the integrity of the duct itself, specifically if the metal duct has a leak, like a break in a joint. This would lead to reduced air flow from pressure loss and potentially allow dust, debris or other materials to enter the duct and come out into the air stream. Another example of a duct issue would be if something upstream of the HVAC system breaks down, such as the blower equipment. This could result in lower airflow and possibly strange odors in the system.
After identifying how the system is compromised, fix the problem and then proceed with cleaning the ducts to ensure the best indoor air quality.
Methods of cleaning
The most commonly used and effective methods for cleaning are contact vacuuming, air washing and power brushing.
Contact vacuuming requires a portable vacuum (like a shop-vac) that is hand operated. The brush head has direct contact with the interior duct surfaces, removing dirt and debris. This method requires larger and multiple openings into the ducts, with work being limited to the vacuum operator’s reach.
Air washing requires compressed air, plus hose and vacuum collection equipment downstream where the debris will be collected. Air washing is done with compressed air and a hose that ends in a “skipper” nozzle. This nozzle is designed so that the compressed air propels it inside the duct while dislodging dirt and debris. The dirt becomes airborne, is drawn downstream through the duct and is removed from the system by vacuum collection equipment.
With power brushing, pneumatically or electrically powered rotation bristle bushes are used to loosen dirt and debris. Like the air washing method, the dirt is then drawn downstream into a vacuum collector. Only soft bristle brushes should be used so that insulation surfaces are not damaged.
Keeping things clean
Something being sanitized is often thought of as the gold standard of clean – but it may not be the best for HVAC ducts. Chemical sanitizing agents can attempt to kill bacteria and other germs, but an expert should weigh in to determine if necessary, and if so, what chemicals to use. If used, building occupants and workers should be protected from exposure to sanitizing agents.
There are sealants marketed to coat and seal duct surfaces, claiming to prevent the release of dust and dirt particles into the air stream, but they’re unnecessary and unproven. Plus, JM’s fiberglass insulation has been carefully engineered with our proprietary antimicrobial Permacote® coating to provide excellent acoustical and thermal performance while keeping fibers out of the airstream, so it doesn’t need additional sealant products.
JM’s fiberglass duct insulation liners are proven safe, so there’s no need for concern about fibers in the airstream. ASTM C1071 standards set stringent requirements for duct insulation materials, and JM’s Linacoustic RC® far surpasses those standards. It has an air erosion rating of up to 15,000 feet per minute (fpm), even though a typical HVAC system operates at velocities ranging from only 400 to 3,000 fpm. During testing the insulation must not break away, crack, peel, flake off or show evidence of delamination or erosion. By achieving such a high air erosion rating, Linacoustic’s safety is clear, and there is no concern about loose fibers that need to be cleared out of the ducts.
Additional resources
Don’t forget, after cleaning a duct system, openings should be properly sealed so that the system’s thermal, acoustical and air-tightness are restored.
This article is based on NAIMA’s manual Cleaning Fibrous Glass Insulated Air Duct Systems, which provides extensive information and illustrations for cleaning insulated duct systems. The Sheet Metal and Air Conditioning Contractors National Association (SMACNA) recommends system design and maintenance procedures in its publication Indoor Air Quality.
And get more information on JM’s duct liner portfolio.
