I!
1 I
1 SO. INCH PEA
4000 BTUH
OIUTLET AIR
I';
,
GAS
WATER
HEATER
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I
f-
ER
f-
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~s
FURNACE
ER
111iI
WATER
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HEATER
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12"
MAX.
1
I
I
I
OUTLET AIR 1 SQ. INCH
PEA2000BTUH
.
INLET AIR 1 SQ. INCH
PEA 2000 BTUH
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, each
opening shall have a minimum
ree area of 1 square inch tor
,,ach 4000 BTUH of total appli-
<-nee input rating in the enclosure.
~
ere are typical duct sizes.
TABLE18
VERTICAL OUTDOOR AIR
OPENING DIMENSIONS
BTUH
Input
45,000
50,000
67,500
75,000
100,000
125,000
150,000
b. Where communicating with
outdoors through HORIZONTAL
DUCTS, each opening shall have
a minimum free area of 1 square
inch for each 2000 BTUH of total
input rating for all equipment in
the enclosure. Here are typical
duct sizes.
TABLE19
HORIZONTAL OUTDOOR AIR
OPENING DIMENSIONS
BTUH
Input
45,000
50,000
67,500
75,000
100,000
125,000
150,000
Method2
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
Free Area Round
Each Opening Pipe Size
22.50 sq. inches
6"
25.00 sq. inches
6"
33.75 sq. inches
7"
37.50 sq. inches 7"
50.00 sq. inches 8"
62.50 sq. inches 9"
75.00 sq. inches 10"
Free Area
Each Opening
11.25 sq. inches
12.50 sq. inches
16.90 sq.
inches
18.75 sq. inches
25.00 sq. inches
31.25 sq. inches
37.50 sq.
inches
Round
Pipe Size
4"
4"
5"
5"
6"
7"
7"
FIGURE 24
OUTSIDE AIR FROM ATTIC/CRAWL SPACE
OUTLET AIR IN
ATTIC MUST BE
ABOVE INSULATION~~---+~
FIGURE 25
OUTSIDE AIR USING A HORIZONTAL
INLET
& OUTLET
OUTLET AIR
1 SO. INCH P
4000 BTUH
INLET AIR
1 SO. INCH P
4000 BTUH
communicate with the outdoors and
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, AND
b. Not less than the sum of the areas
of all vent connectors in the
confined space.
IMPORTANT: IF THE FURNACE IS
IN A LOCATION WITH AN
EXHAUST FAN, THERE MUST BE
GABLE
VENT ·-.
11' !I VE~TILATED
'
1
II --- - ATTIC GABLE OR
I :1- ~- • SOFFIT VENTS
l:iL~1------
\ ~r
~
:c
i=
I ' §
Ii i
FURNJE
~
SUFFICIENT VENTILATION TO
PREVENT THE EXHAUST FAN
FROM CREATING A NEGATIVE
PRESSURE IN THE ROOM.
Combustion air openings must NOT
BE RESTRICTED in any manner.
CONSULT LOCAL CODES FOR
SPECIAL REQUIREMENTS.
Air opening in the furnace casing
front, return air grilles, and warm air
•
registers must not be obstructed.
•
32
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