Which statement is correct regarding the installation of a unit heater attached to a warm air duct system?

Which statement is correct regarding the installation of a unit heater attached to a warm air duct system?

• A. It must be labeled
• B. It must be designed
• C. It must be listed
• D. It must be sized properly

Answer: (C)

The key idea is that equipment used in a HVAC system must be listed by a recognized testing agency for its intended use. Listing shows the unit has been evaluated for safety, performance, and compatibility with the way it will be installed—in this case, mounted on or connected to a warm air duct. This means all aspects—materials, fire safety, electrical or fuel connections, combustion considerations (if gas), venting, and how it interfaces with the ductwork—have been reviewed and approved for that specific installation. Without listing, there’s no independent verification that the unit is safe to operate in that context, which is why listing is required. Labeling or design and sizing each play important roles in safety and performance, but listing specifically provides the installation approval for the device in that configuration.

The key idea is that equipment used in a HVAC system must be listed by a recognized testing agency for its intended use. Listing shows the unit has been evaluated for safety, performance, and compatibility with the way it will be installed—in this case, mounted on or connected to a warm air duct. This means all aspects—materials, fire safety, electrical or fuel connections, combustion considerations (if gas), venting, and how it interfaces with the ductwork—have been reviewed and approved for that specific installation. Without listing, there’s no independent verification that the unit is safe to operate in that context, which is why listing is required.

Labeling or design and sizing each play important roles in safety and performance, but listing specifically provides the installation approval for the device in that configuration.