Empire Comfort Systems BVD34FP30(F,L)N-2 Installation Instructions And Owner's Manual page 13

Model BVD34FP series uses a 4" B-Vent for operation.
Models BVD36FP and BVP42FP series use a 6" B-Vent for
operation.
Clearances
from which maximum vent runs can be determined.
Always maintain minimum clearances or greater around
the vent system. Do not pack air spaces with insulation or
other material.
26534-1-0610
VENTING (CONT)
Figure 15
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