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Fabric Duct Retrofits Can Improve Facility Operations

PHOTO CREDIT: Ductsox Corp.

Forty years after it entered the building industry, fabric duct has become well-known as a new construction alternative to conventional metal ductwork in open architectural ceilings. However, many facility managers aren't aware that fabric air dispersion can also solve many air distribution challenges in existing buildings.

Retrofitting an open architectural ceiling metal duct system with a fabric replacement can provide benefits in reduced maintenance, efficiency, improved performance, air comfort and aesthetics. Furthermore, there are also new innovative upgrades for older, existing fabric duct systems. 


As a retrofit product, fabric duct can easily replace corroded, dirty, dented or biologically contaminated metal duct that has become maintenance intensive. Unlike metal duct, fabric duct does not require protective coatings or painting, and can easily be removed by maintenance people and commercially laundered. Porous versions that are factory-designed to allow approximately 15% of the air to flow through the fabric are the least likely to collect condensation, thus minimizing corrosion and biological contamination that can affect indoor air quality (IAQ). Fabric duct is also available with an optional embedded anti-microbial treatment that deters biological growths and harboring for increased IAQ. 


According to a recent study, fabric duct’s air dispersion is 24.5% more efficient than metal duct/diffusers while heating rooms faster and more uniformly to satisfy temperature set points – which can increase energy savings by reducing mechanical equipment’s runtimes.


Laboratories immersed in state-of-the-art research requiring precise, reduced noise and low air velocities are using fabric duct to minimize skewed results from air flow deficiencies. Labs are typically designed outfitted with conventional four-way diffusers that inherently have excessive velocity, noise or drafts. When throttled with dampers, air flow can cause experiment-disrupting noise and uneven temperature gradients and drafts. The fabric duct industry has accommodated requests for better lab air distribution by developing a fabric retrofit for 2 x 2-foot, 2 x 4-foot and larger diffusers that consists of a fabric, framework and/or back pan replacement which distribute the air evenly and with less velocity to create the perfect lab environment. Commercial kitchens also suffer from similar exhaust hood air flow challenges. Replacing conventional ceiling air distribution with fabric diffusers to reduce velocities and minimize turbulence can allow kitchen cooking hoods to draft efficiently and create better IAQ for employees and patrons.

Most cooking produces some type of smoke, steam or some type of effluent that needs to be captured.  There's a good chance that many restaurant or foodservice refrigeration contractors may have customers unhappy with hood capture or air comfort in a commercial kitchen.  These customers may think cleaning excessive grease off wall and poor kitchen IAQ is an inherent part of the foodservice business, however the solution may be a simple airflow issue.  A good estimate is that at least 40-percent of commercial kitchens in restaurants and foodservice outlets don't have properly functioning ventilation systems.   

Commercial kitchen ventilation challenges are similar to labs in that excessive HVAC supply air can disrupt cooking hood capture.  The main reasons are:  

  • Kitchen exhaust and HVAC supply air systems are commonly installed by separate contractors.  While owners may focus and invest heavily in capture hood technology, there is a clear disconnect on how or where airflow enters the space and how it impacts hood capture, employee comfort or food quality.
  • Restaurants many times outgrow their original kitchen design by adding more cooking hoods and/or heat-producing appliances that skew the original ventilation specifications. Adding more cooking hoods in a remodel or update can also impinge uniform supply air distribution or offset building pressurization.

Poorly balanced ventilation systems -- either by design or installation oversight--can skew a kitchen's critical air pressure from negative to positive. They should be operating under a negative pressure, however once installed or remodeled, they can be inadvertently skewed to a positive pressure, which impedes the cooking hood's ability to exhaust properly and prevent smoke and cooking odor infiltration into the dining area. An example is a cooking hood exhausting 3,000-cfm in a kitchen that's supplied with 2,500-cfm of make-up air and a kitchen HVAC system supplying 1,000-cfm into the kitchen. Consequently the kitchen's negative pressure turns positive as the extra 500 to 1,000-cfm of supply air pushes the kitchen odors, grease and heat into the dining area.

Air Comfort:

Under floor air distribution (UFAD) is a popular raised-floor construction model in office buildings and other commercial spaces because of reconfiguration and cable management flexibility. However, UFAD can suffer unintended temperature gain as supply airflow within the plenum and doesn't reach all floor diffusers or perimeter areas. This setback is caused by either heat energy transferring to the slab from the floor below or solar gain from the perimeter. When the building management boosts air conditioning to offset the heat gain, occupants near the core or middle of the building many times feel chilled. These temperatures can reach up to a 16 degree Fahrenheit differential from diffuser to diffuser. Besides overcooling, the temperature increase can raise air conditioning operational costs as much as 40%, not to mention premature HVAC equipment wear-and-tear or failure.

One solution is specially-designed textile duct connected to the plenum supply or directly to plenum air distribution highways anywhere within the UFAD. Because they're flexible 12 to 18-inch-diameter round fabric ducts, they can be routed around UFAD obstacles such as cables, raised floor support pedestals or utility piping. The modular sections of fabric can include linear vents where needed to ensure a proper air mix. This results in more stable and efficient diffuser discharge temperatures throughout the UFAD system.


Perhaps the only drawback to fabric duct is its deflated appearance during idle air handler periods or a distracting inflation during system start-ups. In-duct tensioning systems can combat this problem for both new construction and retrofits. These lightweight metal framework systems are inserted into fabric duct to create a rigid, taut and unwrinkled appearance regardless of whether the air handler is idle.They're easily installed into duct diameters ranging from 18 to 84-inches, depending on the style of in-duct tensioning system used. 

Aside from the efficiency benefits, perhaps the greatest attribute for the retrofit of metal to fabric is the ease of installation. While installing metal duct, which is generally 90% heavier than fabric, requires movement of shelves, machines, processes and other obstacles for scaffolding and scissor lifts, nearly all diameters of fabric are light enough to install from ladders by just two people.

While building air distribution systems may appear to be permanent and incapable of upgrading, fabric duct retrofits can deliver improvements in maintenance, efficiency, performance, air comfort and aesthetics.

Nick Kaufmann is director of manufacturing and engineering at DuctSox Corp. Reach him at

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