Isolating Vibrations And Noises with Flexible Duct Connectors

A flexible duct connector is an airtight, flexible joint consisting of a fabric that is secured to sheet metal on both sides (figure 1). These are used as an attachment between the equipment and the ductwork to isolate the vibrations and noises in a duct system (figure 2). Flexible duct connectors, unlike hard duct, also allow for a slight offset between the equipment and ductwork.

Flexible duct connectors are manufactured in varying sizes and thickness for use in residential, light commercial, commercial and industrial applications. Fabric-to-metal joining method is important. You want a permanent, air-tight joint. The type of joint used will also impact the structural rigidity of the connector.

There are many flexible duct connectors available with a wide array of joining methods, such as Single Fold Seam (figure 5). Our DynAir Flexible Duct Connectors use a double-fold offset seam (figure 3) in all of our flexible duct connector products. This connection style ensures that you will have an airtight seal that cannot be damaged when the connector is fabricated into its final shape. The double-fold offset seam also adds structural stability to the connector, which means that the connector will not fail due to over- or under-pressure issues. DynAir also offers the Fab Guard seam (figure 4) for additional fabric protection.

Is the metal used important?  

Yes, the metal comprises two-thirds of the flexible duct connector assembly so it is key for a long-lasting connection. The standard metal used in flexible duct connectors is galvanized steel. When looking at galvanized steel, you have to consider the coating thickness and how this impacts the metal’s longevity and the installation location. The two most commonly used galvanized steel grades in HVAC are notated as G60 and G90. The 60 and 90 refer to the total amount of zinc deposited on the surface of the steel; G90 has a thicker coating and therefore will last longer. In indoor applications G60 will have two-thirds the life expectancy of G90, which means that G90’s indoor life expectancy is 20 years longer than that of G60. For outdoor applications the full life expectancy drops dramatically but you will still see G90 outlasting G60 (reference). SMACNA (The Sheet Metal and Air Conditioning Contractors’ National Association) recommends in the “Duct Construction Standards – Metal and Flexible” standard to use a minimum of G60 for ductwork and connectors. The ASHRAE Handbook—under “HVAC Systems and Equipment”, Chapter 16 “Duct Construction”—recommends to a use minimum of G90 for ductwork and connectors. Even though G90 is not required per SMACNA, DynAir understands the need to manufacture a quality product that will last and has standardized G90 for all of our duct connectors.  

Will the flexible duct connector impact the airflow through the duct system?

A properly installed flexible duct connector will not impede airflow through the duct system. It is important to size and install the flexible duct connector to fit the distance the fabric will be spanning (figure 7). If the fabric is allowed to droop or accordion too much it can impact the airflow through the connector (figure 8).

How do I choose the right flexible duct connector?

There are several key factors that will determine which flexible duct connector is right for your job. What pressure will the duct system be running at? Will the equipment be installed within the building envelope or outside of the building? What are the typical minimum and maximum temperatures the ductwork will be exposed to? Will the flexible duct connector be exposed to additional constituents in the airstream (chemicals, etc.)? How large of a distance do you need to span? These are just a few of the important factors to consider. The table below will give you the information you need to select appropriately.