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Exhaust through Crawl Space Vent Option
All 33" condensing gas furnaces (92%+) are now approved
to be vented down through a crawl space. Ensure a vent
pipe drain kit, 51W18 (USA) or 15Z70 (Canada), is used as
directed through the floor joists and into the crawl space.
See the following figures.
Consult the vent tables for vent lengths and approved
materials.
2" or 3"
Sanitary Tee
1/2" PVC
Drain Stub
Drain Trap
Assembly
Rubber Boot (51W18)
Drain Plug (15Z70)
Clamp
(51W18 Only)
Figure 33. Kit 51W18 (USA) / 15Z70 (Canada) Parts
Identification and Assembly
NOTE:
Upflow furnaces exhaust from the left side. All dimensions shown are typical for upflow or downflow furnaces.
NOTE:
All horizontal runs of exhaust pipe must slope back toward the kit a minimum of 1/4" (6mm) for each 12" (305mm) to ensure drainage.
Figure 35. Upflow or Downflow Furnace with Exhaust through Crawl Space
Page 24 of 73
From
To Vent
Furnace
Termination
Drain Trap
(assembled)
Downflow Furnace
Exhaust
KIT 51W18 (USA)
KIT 15Z70 (Canada)
Exhaust from
Furnace
Exhaust from
Furnace
Figure 34. Crawl Space Vent Pipe Drain Trap
24" max.
* Kit 51W18 is shown.
Basement Floor
Issue 2241
To Termination
* Kit 51W18 is shown.
Assembled Incorrectly
To Termination
1/2" PVC to
Code-Approved
Drain
To Termination
507029-05
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