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SUPPLY
AIR
INTERIOR
HEATED
SPACE
RETURN AIR
* Minimum opening size is 100 sq. in. with
minimum dimensions of 3-In.
NOTE:
Side clearance required as needed for
combustion-air pipe and termination,
vent pipe, and gas and electrical connections.
Fig. 12—Confined Space: Air for Combustion and
Ventilation from an Unconfined Space
hallway or space adjacent to the furnace, all air for combustion
must come from outdoors. (See Fig. 13.)
ALL AIR FROM OUTSIDE THE STRUCTURE
1. If combustion air is taken from outdoors through vertical
ducts, the openings and ducts MUST have at least 1 sq in. of
free area per 4000 Btuh of the total input for all equipment
within the confined space. (See Fig. 13.)
For Example:
COMBUSTION AIR FROM OUTDOORS THROUGH
VERTICAL DUCTS
58MSA Furnace
Free Area per Opening
Input Btuh
40,000
60,000
80,000
100,000
120,000
2. If combustion air is taken from outdoors through horizontal
ducts, the openings and ducts MUST have at least 1 sq in. of
free area per 2000 Btuh of the total input for all equipment
within the confined space. (See Fig. 13.)
VENT THROUGH ROOF
OR SIDEWALL
12" MAX
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
UNCONFINED
SPACE
3" MIN
(FRONT)
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
12" MAX
Round Pipe
(Sq In.)
(In. Dia)
10.0
4
15.0
5
20.0
6
25.0
6
30.0
7
OUTDOORS
12" MAX
1 SQ IN.
PER 2000
A
BTUH *
DUCTS
TO
OUTDOORS
1 SQ IN.
PER 2000
B
BTUH *
12" MAX
RETURN AIR
* Minimum dimensions of 3-In.
NOTES:
1. Use any of the following
combinations of openings:
A & B
C & D
2. Side clearance required as needed for
combustion-air pipe and termination,
vent pipe, and gas and electrical connections.
A96185
Fig. 13—Confined Space: Air for Combustion and
Ventilation from Outdoors
For Example:
COMBUSTION AIR FROM OUTDOORS THROUGH
58MSA Furnace
Input Btuh
40,000
60,000
80,000
100,000
120,000
3. When ducts are used, they must be of the same cross-sectional
area as the free area of the openings to which they connect.
The minimum dimension of ducts must not be less than 3 in.
(See Fig. 13.)
Step 1—Leveling Legs (If Desired)
When furnace is used in upflow position with side inlet(s), leveling
legs may be desired. (See Fig. 14.) Install field-supplied,
corrosion-resistant 5/16-in. machine bolts and nuts.
NOTE: The maximum length of bolt should not exceed 1-1/2 in.
14
DUCTS
TO
D
VENT
THROUGH
SUPPLY
ROOF
AIR
OR
SIDEWALL
E
C
12" MAX
DUCT
TO
OUTDOORS
D & E
F & G
HORIZONTAL DUCTS
Free Area per Opening
(Sq In.)
20.0
30.0
40.0
50.0
60.0
INSTALLATION
1 SQ IN.
PER 4000
BTUH *
12"
MAX
F
1 SQ IN.
PER 4000
BTUH *
1 SQ IN.
PER 4000
BTUH *
G
12"
MAX
1 SQ IN.
PER 4000
BTUH *
A96186
Round Pipe
(In. Dia)
6
7
8
8
9
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