Bradford White THROUGH-THE-WALL GAS WATER HEATER Install And Operation Instructions page 16

When venting cannot exit through the wall at a height greater than or equal to 12"
(30.5 cm) above the ground, or anticipated snow level, the installation must be
modified as shown below (see Figure 5). Refer to Table 4 for maximum venting
lengths using 3" (7.6 cm) PVC or Table 5 for maximum lengths using 4" (10.2 cm)
PVC.
Figure 5
Venting (Part I) continued-
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