Thermaflex 53709000002 Insulated Flex Duct 9 in X 25 Ft R-4.2

Product Description

The THERMAFLEX 53709000002 is a 9-inch diameter, 25-foot insulated flexible air duct designed for low- to medium-pressure HVAC distribution systems. The KM series innercore is constructed from a smooth polyester film laminated over a heavy-gauge, corrosion-resistant steel wire helix. This design maintains duct shape under normal system pressures while delivering an airtight airflow path. A thick fiberglass insulation blanket surrounds the core, rated at R-4.2, providing thermal resistance to reduce heat gain or loss between the air handler and diffuser. HVAC technicians and sheet metal contractors install this product in residential and light commercial ducted systems.

This flexible duct is suited for branch-run applications in forced-air heating and cooling systems, including residential new construction and retrofit installations. It is commonly routed from a main trunk line or plenum to individual supply registers. The 9-inch diameter accommodates higher-volume supply runs typical in larger residential zones or light commercial spaces. The 25-foot coil length reduces the need for mid-run connections on longer branch runs, minimizing potential leakage points.

Key Features

• R-4.2 fiberglass insulation blanket reduces heat transfer along the duct run
• Smooth polyester film innercore supports low-friction airflow in low- to medium-pressure systems
• Heavy-gauge, corrosion-resistant steel wire helix maintains duct shape and prevents collapse
• Bi-directional reinforced metallized outer vapor barrier resists moisture infiltration and will not unravel
• 25-foot coil length reduces mid-run splices on longer branch applications

Compatibility

Designed as an OEM-style flexible duct for residential and light commercial forced-air supply distribution systems with 9-inch round duct connections operating at low to medium static pressure.

Installation Notes

Installation should be performed by a licensed HVAC technician or qualified sheet metal contractor in accordance with ACCA Manual D and applicable local mechanical codes. Power down the air handling system at the disconnect or breaker before making duct connections. Avoid sharp bends and keep the duct as fully extended as practical to minimize airflow restriction and condensation risk. Secure both ends with approved draw bands and mastic or listed duct tape rated for flexible duct applications.