High-efficiency furnaces vent exhaust gases through which type of piping?

• A. Cast iron
• B. PVC
• C. Steel
• D. Copper

Answer: (B)

Venting for high-efficiency furnaces uses plastic piping because their exhaust gases are cool and moisture-rich. These condensing furnaces push exhaust at relatively low temperatures, often around 100–140°F, which means non-metallic piping like PVC can withstand the heat without deforming. The exhaust also contains condensate from the combustion process, which is mildly acidic; PVC resists this acidic condensate and remains durable over time. PVC is also lighter, easier to install, and typically cheaper than metal venting.

In contrast, older non-condensing furnaces produce hotter exhaust that can reach several hundred degrees Fahrenheit, so metal venting such as cast iron or steel is required to handle the high temperatures and prevent failure. Always follow the appliance manufacturer’s venting guidelines and local codes, including proper vent material and the slope needed to drain condensate.