Rheem GF951U Series - Page 17

17
B
TUH Free Area
I
nput Each Opening
4
5,000 100 square inches
6
0,000 100 square inches
7
5,000 100 square inches
90,000 100 square inches
105,000 105 square inches
B. USING OUTDOOR AIR FOR
COMBUSTION
!%('*,&,Do not take air from
an attic space that is equipped
with power ventilation.
The confined space must
communicate with the outdoors in
accordance with Methods 1 or 2.
The minimum dimension of air
openings shall not be less than 3
inches. Where ducts are used,
they shall be of the same cross-
sectional area as the free area of
the openings to which they
connect.
Method 1
Two permanent openings, one
located within 12 inches of the top
and one located within 12 inches
of the bottom of the enclosure,
shall be provided. The openings
shall communicate directly, or by
ducts, with the outdoors or spaces
(crawl or attic) that freely
communicate with the outdoors.
a. Where directly communicating
with the outdoors or where
communicating to the outdoors
through vertical ducts as shown in
Figure 12, each opening shall
have a minimum free area of 1
square inch for each 4,000 BTUH
of total appliance input rating in the
enclosure.
BTUH Free Area Round Pipe
Input Each Opening Size
45,000 11.25 square inches 4"
60,000 15.00 square inches 5"
75,000 18.75 square inches 5"
90,000 22.50 square inches 6"
105,000 26.25 square inches 6"
b. Where communicating with
outdoors through horizontal ducts,
each opening shall have a
minimum free area of 1 square
inch for each 2,000 BTUH of total
input rating of all equipment in the
enclosure (Seee Figure 13).
Here are some typical sizes:
BTUH Free Area Round Pipe
Input Each Opening Size
45,000 22.50 square inches 6"
60,000 30.00 square inches 6"
75,000 37.50 square inches 7"
90,000 45.00 square inches 8"
105,000 52.50 square inches 8"
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