CleaverBrooks CFC-500 Operation, Service And Parts Manual page 66

Section 3 — Stack and Intake Vent Sizing and Installation
3-16
GAS
VENT
CLEARFIRE
BOILER
Figure 3-6. Two Opening Ducted Method
C. One Opening Method (Figure 3-7) - One permanent opening,
GAS
VENT
INTERIOR WALL
EXTERIOR WALL
WATER
HEATER
commencing within 12 inches of the top of the enclosure,
shall be provided.
1. The equipment shall have clearances of at least 1 inch
from the sides and back and 6 inches from the front of
the appliance.
2. The opening shall directly communicate with the
outdoors and shall have a minimum free area of 1 square
inch per 3000 BTU's per hour of the total input rating of
all equipment located in the enclosure, and not less than
the sum of the areas of all vent connectors in the confined
space.
3. Refer to the NFGC, Section 8.3 for additional
information.
12" MINIMUM
OUTLET AIR DUCT
FRESH AIR
INLET DUCT
12" MINIMUM
Part No. 750-263