Non-direct vent (single pipe) termination

What is going on

Non-direct vent, single pipe, means the furnace pulls its combustion air from the room and only the flue pipe goes outside. It can exit horizontally through a side wall, vertically through the roof, or run up an unused chimney with at least 12 in. above the chimney top. The usual headaches are snow burying the termination and weather leaking in around the penetration.

Likely causes

• Termination too low and buried by snow
• Unsealed roof or chimney penetration leaking weather in
• Elbow or tee pointing up on a wall exit, letting rain in
• Gap around the pipe in the chimney left open

Check in this order

1. Keep the termination at least 12 in. above the highest anticipated snow level.
2. For a vertical roof exit, seal the penetration with flashing such as used for plastic plumbing vents.
3. For a horizontal wall exit, use the termination shown in the figure and point any elbow or tee downward.
4. For a chimney run, seal the gap between pipe and chimney with weather-tight, corrosion-resistant flashing.
5. Check that the room supplies adequate combustion air for a non-direct vent system.
6. After install, inspect the termination from outside during a heat call.

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)