Which venting system operates at less than 140° F due to its unique design characteristics?

The correct answer is based on the specific characteristics of venting systems categorized under the different standards set for gas appliances. Category 2 venting systems are designed to operate at temperatures less than 140° F. This is primarily because they utilize a type of appliance that is categorized as "fan-assisted," which ensures that the combustion gases are expelled efficiently without reaching high temperatures.

This configuration allows for the use of plastic venting materials, which are safe and effective at these lower temperatures, offering a practical solution for venting appliances designed to operate efficiently. The cooling of gases before they enter the vent system is crucial to maintain these lower operating temperatures, making Category 2 systems suitable for installations where heat exchanger temperatures must be controlled to prevent damage or leaks.

In contrast, other categories, such as Category 1, Category 3, and Category 5, generally operate at higher temperatures due to different design requirements and application scenarios, which do not align with the low-temperature characteristics of Category 2 systems.