Which factor describes a Category 1 venting system?

A Category 1 venting system is characterized by operating at negative pressure and requiring that the flue gas temperature be maintained at least 140°F above the flue gas dew point. This design helps prevent condensation within the venting system. By ensuring that the temperature differential is substantial, it mitigates the risk of moisture in the exhaust gases condensing and causing corrosion or blockages within the flue.

This design is typical for appliances that do not have fans for forced venting, relying instead on natural draft to move exhaust gases outside. Thus, the adequate temperature maintenance ensures effective venting performance and longevity of the venting materials.

The other options either misrepresent the pressure conditions or temperature requirements associated with Category 1 systems.