Venting below grade and outdoor vent piping

What is going on

Vent pipe that leaves the building below grade, or runs outside the wall before it terminates, has tighter limits than a normal indoor run. Before touching anything, confirm exactly which section of the vent sits outdoors and how much of it counts toward the total vent length. These limits apply to the NTI TRX150.

Likely causes

• Vent exits the foundation below grade and ground water or soil can reach the penetration
• Long outdoor run exposed to cold, so condensate can freeze or pool in the pipe
• Unsupported or level outdoor pipe that sags and traps condensate

Check in this order

1. Excavate down to the point where the pipes exit so you can see the whole penetration.
2. Seal the wall fully where the pipes pass through.
3. Secure the exhaust and intake to the side of the building above grade.
4. Keep all the normal termination clearances.
5. Limit piping outside the building to 20 ft, and include that length in the total vent length.
6. Support the outdoor pipe every 24 in.
7. Slope the exhaust and intake back toward the boiler at 1/2 in per linear foot so condensate drains to the boiler.

More boiler guides

• Access the low voltage wiring connections
• Blocking errors versus lockout errors
• Blower not running
• Blower runs at high speed with burner off
• Boiler bangs or hisses; Lockout 81 delta T
• Burner not running on a call for heat