A unit heater shall not be attached to a warm air ducts system unless ______ for such an installation.

A unit heater shall not be attached to a warm air ducts system unless ______ for such an installation.

• A. designed
• B. listed
• C. labeled
• D. sized properly

Answer: (B)

The requirement hinges on safety certification for the specific installation. A unit heater may only be connected to a warm air duct system if it has been evaluated and approved for that use by a recognized testing organization—i.e., it must be listed for such installation. Listing means the unit has been tested for performance, compatibility with duct systems, fire and heat concerns, materials, clearances, and overall safety in that setup. Without listing, the installation could pose safety risks and may not meet code or warranty terms. Saying it’s merely designed doesn’t guarantee third‑party evaluation for duct connections. Being labeled implies a marking on the unit but doesn’t confirm it’s approved for duct‑system installation. Being sized properly relates to capacity, not to the safety certification required for attaching to ductwork. Listing specifically ensures the unit is approved for use with warm air duct systems.

The requirement hinges on safety certification for the specific installation. A unit heater may only be connected to a warm air duct system if it has been evaluated and approved for that use by a recognized testing organization—i.e., it must be listed for such installation. Listing means the unit has been tested for performance, compatibility with duct systems, fire and heat concerns, materials, clearances, and overall safety in that setup. Without listing, the installation could pose safety risks and may not meet code or warranty terms.

Saying it’s merely designed doesn’t guarantee third‑party evaluation for duct connections. Being labeled implies a marking on the unit but doesn’t confirm it’s approved for duct‑system installation. Being sized properly relates to capacity, not to the safety certification required for attaching to ductwork. Listing specifically ensures the unit is approved for use with warm air duct systems.