Non-direct vent: alternate horizontal termination

What is going on

This is the alternate horizontal terminal for a non-direct vent install, where the furnace draws combustion air from the room and only the exhaust goes outside. The one I get asked about is the height above grade. Keep the bottom of the termination at least 12 in (31 cm) above grade or the highest expected average snow level, whichever is higher, because buried vents are how people end up with blocked flues in February. In Canada, the termination must meet CSA B149.1-10, Sect. 8.14. A field-supplied reducing coupling is used where the pipe size changes, and a 2 in run of up to 18 in is allowed before the wall penetration when 3 in vent is used.

Likely causes

• Site with deep snow or low grade where the terminal could get buried
• Install in Canada where the code reference applies
• Pipe size change from 3 in to 2 in near the wall
• Alternate termination chosen because the standard one will not fit the wall layout

Check in this order

1. Keep the termination at least 12 in above grade or expected snow level
2. In Canada, follow CSA B149.1-10, Sect. 8.14
3. Use a field-supplied reducing coupling to step from 3 in to 2 in pipe
4. Limit 2 in pipe inside the building to 18 in before the penetration when using 3 in vent
5. Seal the wall penetration and support the pipe so it holds its slope
6. Have the finished vent inspected where local code requires it

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