Which of the following is a required characteristic of vent materials used with wall furnaces?

The required characteristic of vent materials used with wall furnaces is that they must have labeling and listing for use. This means that the materials must be certified by an appropriate authority to ensure they meet specific safety and performance standards. This is essential to guarantee that the venting system operates effectively and safely, minimizing the risks associated with gas combustion and exhaust.

Labeling and listing ensure that the materials used are recognized and approved for their intended purpose, providing assurance to both installers and homeowners. This characteristic is crucial because improperly specified materials could lead to safety hazards, such as carbon monoxide leaks or system failures.

While flexibility, durability, and cost-effective manufacturing are important considerations in material selection, they do not carry the same regulatory requirement as being labeled and listed. Properly certified materials are vital for compliance with building codes and standards, which are designed to protect health and safety.