Plenum-Rated Pipe and Duct Insulation Defined

Plenum spaces in buildings are designed to discreetly house building systems such as HVAC equipment & return airflow, pipe runs, and digital cables. Although air plenums are typically out-of-sight, typically located above ceiling grids or in under-floor systems, mechanical design and plenum-rated pipe and duct insulation are critically important to ensure the safety of building occupants and the building itself.

Since air plenums house HVAC systems that require airflow, they present an oxygen-rich environment in which fire and smoke has the potential to spread through the plenum and into occupant spaces (through ductwork for example) risking life safety.

How Do You Identify Plenum-Rated Pipe and Duct Insulation?

Most U.S. building codes reference the International Mechanical Code (IMC) which provides specific requirements for acceptable building components to be specified and installed in plenums. The 2018 IMC Section 602.2.1.8 Pipe and duct insulation within plenums specifies the following requirements:

“Pipe and duct insulation contained within plenums, including insulation adhesives, shall have a flame spread index of not more than 25 and a smoke-developed index of not more than 50 when tested in accordance with ASTM E84 or UL 723, using the specimen preparation and mounting procedures of ASTM E2231. Pipe and duct insulation shall not flame, glow, smolder or smoke when tested in accordance with ASTM C411 at the temperature to which they are exposed in service. The test temperature shall not fall below 250°F(121°C). Pipe and duct insulation shall be listed and labeled.”

This is the most accurate definition of “plenum-rated” insulation so let’s break this down. First and foremost, plenum-rated pipe and duct insulation must pass ASTM E84 Standard Test Method for Surface Burning Characteristics of Building Materials or UL 723 Standard for Test for Surface Burning Characteristics of Building Materials. Essentially, ASTM E84 and UL 723 are the same. The flame spread index must be not more than 25, and the smoke developed index must not be more than 50. This is what is commonly referenced as “25/50” or “25/50-rated”.

Secondly, plenum-rated pipe and duct insulation shall not flame, glow, smolder or smoke when tested according to ASTM C411, and the continuous test temperature shall not fall below 250°F (121°C).

Finally, a new IMC requirement of plenum-rated pipe and duct insulation is that it be “listed” and “labeled”. What does this mean? Listed means that the manufacturer’s plenum-rated pipe and/or duct insulation is listed on a third-party test agency’s website under their “listing directory.” Labeled means that the manufacturer’s packaging references compliance with ASTM E84 and/or UL 723.

Aeroflex’s Aerocel® brand of plenum-rated pipe and duct insulation passes ASTM E84 25/50 up to 2” [50mm] thick. Since our EPDM formula has an upper continuous service temperature of 257°F (125°C), it meets ASTM C411. Aerocel will soon be listed on our test agency’s website. In the meantime, an ASTM E84 test report is available upon request at https://www.aeroflexusa.com/contact-us. Finally, all Aerocel plenum-rated pipe and duct insulation packaging references compliance with ASTM E84, and the orange trademark on our tubes does as well.

To learn more about Aeroflex’s plenum-rated insulation solutions, please visit https://www.aeroflexusa.com/aerocel-hvac-pipe-insulation.

Source: 2018 International Mechanical Code