White Mountain Hearth DVTL27FP90N-1 Installation Instructions And Owner's Manual page 17

Vent pipe Clearance
Note: Maintain all clearances to combustibles as shown in
Figures 1 and 2 on page 8.
For horizontal vent, maintain a minimum 1 inch clearance to
the bottom and sides of the vent, and 3 inches of clearance to
combustibles above the vent pipe. See Figure 24.
33740-7-0515
INSTALLATION (continued)
Figure 22
Figure 23
HORIZONTAL VENT CLEARANCES
Figure 24
Page 17