What category does the Natural Fuel Gas code classify a vent system for a condensing furnace?

A vent system for a condensing furnace is classified as Category IV. This classification is designated for appliances that produce flue gases with a low temperature and high efficiency, typically under 55°C (130°F). Such systems are designed to use PVC, CPVC, or other non-metallic materials for venting because the exhaust gases lack significant heat, reducing the risk of damage and corrosion that might occur with traditional metal venting systems.

This category allows for direct venting, meaning that the system can draw combustion air from the outside and discharge exhaust gases outside as well, promoting greater efficiency and safety. Unlike other categories, which may have more stringent venting requirements due to higher temperatures or other characteristics, Category IV vent systems can operate optimally under these conditions, maximizing efficiency and minimizing the environmental impact.