Crown Boiler BWF Series Installation Instructions Manual page 18

6. Vent System Design (continued)
'Y' 'X' Max. Overhang
0 - 12" NOT PERMITTED
12 - 48" 17 - 29" X minus 7"
Greater than 48" 17 - 29" 36"
Note: Overhang may not be ventilated if 'Y' is less than 48"
Figure 6.9c: Location of Vent Terminal Under Overhangs
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109836-01 - 04/20