How are flexible ducts designed?

How are flexible ducts designed?

• A. Contain a foam core with no jacket
• B. Have an insulated outer jacket surrounding a plastic film coil spring inner liner.
• C. Use bare metal with no insulation
• D. Are made of solid concrete

Answer: (B)

Flexible ducts are designed to carry air while staying bendable, so they need both a contained airflow path and thermal protection. The typical layout places a plastic film inner liner that contains the air, supported by a coil spring to keep the duct from collapsing when it’s bent. Around that inner assembly sits an insulated outer jacket, which minimizes heat transfer and helps prevent condensation on the duct surface. This combination—an insulated outer jacket surrounding a plastic film inner liner with a coil spring for support—provides the right balance of flexibility, airflow containment, and thermal protection. Other options either omit insulation, use an inappropriate core, or rely on materials not suitable for HVAC ductwork, making them unsuitable for flexible ducts.

Flexible ducts are designed to carry air while staying bendable, so they need both a contained airflow path and thermal protection. The typical layout places a plastic film inner liner that contains the air, supported by a coil spring to keep the duct from collapsing when it’s bent. Around that inner assembly sits an insulated outer jacket, which minimizes heat transfer and helps prevent condensation on the duct surface. This combination—an insulated outer jacket surrounding a plastic film inner liner with a coil spring for support—provides the right balance of flexibility, airflow containment, and thermal protection. Other options either omit insulation, use an inappropriate core, or rely on materials not suitable for HVAC ductwork, making them unsuitable for flexible ducts.