Empire Comfort Systems BF28(B,C,G)M(N,P)-5 Installation Instructions Manual page 22

PVVK-24H AND PVVK-48H CO-AXIAL VENT KIT (cont.)
Horizontal Venting Maximum 47.5" (1.2 m) with 45° elbows.
Inner 1-1/2 inch pipe and outer 3 inch pipe 45° elbows can be
purchased from a local hardware store.
Direct Vent System Building Exterior View
Maximum Horizontal Venting - 47 1/2" (1.2 m)
Minimum Horizontal Venting - 4" (10.2 cm)
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