Rheem RGFG Installation Instructions Manual page 16

b. Where communicating with out-
doors through horizontal ducts,
each opening shall have a minimum
free area of 1 square inch for each
2000 BTUH of total input rating of
all equipment in the enclosure. See
Table 5 and Figure 8.
TABLE 5
HORIZONTAL OUTDOOR AIR
OPENING DIMENSIONS
BTUH Free Area
Input Each Opening
60,000 30.00 square inches
75,000 37.50 square inches
90,000 45.00 square inches
105,000 52.50 square inches
120,000 60.00 square inches
Method 2
One permanent opening, located
within 12 inches of the top of the
enclosure, shall be permitted where
the equipment has clearances of at
least 1 inch from the sides and back
and 6 inches from the front of the
appliance. The opening shall directly
communicate with the outdoors or
communicate through a vertical or
horizontal duct to the outdoors or
spaces (crawl or attic) that freely
communicate with the outdoors, and
shall have a minimum free area of:
a. One square inch for each 3000
BTUH of the total input rating of
all equipment located in the
enclosure (see Table 6), and
b. Not less than the sum of the
areas of all vent connectors in the
confined space.
If the unit is installed where there is
an exhaust fan, sufficient ventilation
must be provided to prevent the
exhaust fan from creating a negative
pressure.
TABLE 6
VERTICAL OR HORIZONTAL
OUTDOOR AIR OPENING DIMENSIONS
BTUH Free Area
Input Each Opening
60,000 20.00 square inches
75,000 25.00 square inches
90,000 30.00 square inches
105,000 35.00 square inches
120,000 40.00 square inches
16
Combustion air openings must not be
restricted in any manner.
CONSULT LOCAL CODES FOR SPE-
CIAL REQUIREMENTS.
FIGURE 7
AIR FROM ATTIC/CRAWL SPACE
Round Pipe
Size
7"
7"
8"
9"
9"
FIGURE 8
OUTSIDE AIR USING A HORIZONTAL INLET & OUTLET
Round Pipe
Size
6"
6"
7"
7"
8"
A077601
A077701