A concentric vent is a pipe-within-a-pipe configuration where the exhaust pipe runs through the center of a larger intake pipe, allowing combustion air intake and exhaust discharge through a single wall penetration. This sealed combustion design prevents indoor air from being drawn into the furnace or water heater. Concentric vents are standard in high-efficiency direct vent appliances.
Design and Construction
The inner pipe, typically 2 to 3 inches in diameter, carries hot exhaust gases at temperatures of 100 to 150 degrees Fahrenheit. The outer pipe, usually 4 to 6 inches in diameter, draws fresh outdoor air to the appliance through the annular space between pipes. PVC or metal construction materials are commonly used depending on exhaust temperature requirements.
Practical Advantages
Concentric vents require only a single roof or wall penetration, simplifying installation and reducing building envelope disruption. They work effectively on exterior walls, allowing shorter vent runs and better aesthetics. The configuration ensures equal intake and exhaust capacity, maintaining system balance. Concentric vents are ideal for sidewall installations in apartments, townhomes, and modern residential construction where space and appearance are important considerations.