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Step 3—Supply Air Connections
DOWNFLOW FURNACES
Connect supply-air duct to supply-air opening on furnace. The
supply-air duct attachment must ONLY be connected to furnace
supply/outlet or air conditioning coil casing (when used), when
installed on non-combustible material. When installed on combus-
tible material, supply-air duct attachment must ONLY be con-
nected to an accessory subbase or factory approved air condition-
ing coil casing. DO NOT cut main furnace casing to attach supply
side air duct, humidifier, or other accessories. All accessories
MUST be connected external to furnace main casing.
HORIZONTAL FURNACES
Connect supply-air duct to supply air opening on furnace. The
supply-air duct attachment must ONLY be connected to furnace
supply/outlet or air conditioning coil casing (when used). DO NOT
cut main furnace casing to attach supply side air duct, humidifier,
or other accessories. All accessories MUST be connected external
to furnace main casing.
Step 4—Return Air Connections
The return-air duct must be connected to return-air opening
provided as shown in Fig. 1. DO NOT cut into casing sides or back
to attach any portion of return-air duct. Bypass humidifier connec-
tions should be made at ductwork or coil casing sides exterior to
furnace.
Fig. 3—Confined Space: Air for Combustion and
Ventilation from an Unconfined Indoor Space
A93387
RETURN
AIR
6″ MIN
(FRONT)
†
SUPPLY AIR
VENT THROUGH ROOF
(CATEGORY I)
1 SQ IN.
PER 1000
BTUH
*
IN DOOR
OR WALL
12
″
MAX
1 SQ IN.
PER 1000
BTUH
*
IN DOOR
OR WALL
12
″
MAX
INTERIOR
HEATED
SPACE
* Minimum opening size is 100 sq in. with
minimum dimensions of 3 in.
†
Minimum of 3 in. when type B-1 vent is used.
UNCONFINED
SPACE
Fig. 4—Confined Space: Air for Combustion and
Ventilation from Outdoors
A93388
DUCTS TO
OUTDOORS
1 SQ IN.
PER 4000
BTUH
*
RETURN
AIR
VENT
THROUGH
ROOF
(CATEGORY I)
D
B
A
C
E
1 SQ IN.
PER 4000
BTUH
DUCT
TO
OUTDOORS
SUPPLY AIR
1 SQ IN.
PER 2000
BTUH
*
DUCTS
TO
OUTSIDE
12″ MAX
12″ MAX
CONFINED
SPACE
12
″
MAX
12
″
MAX
1 SQ IN.
PER 4000
BTUH
*
OUTDOORS
1 SQ IN.
PER 4000
BTUH
*
1 SQ IN.
PER 2000
BTUH
*
12″ MAX
Use any of the following
combinations of openings:
A & B C & D D & E F & G
NOTE:
*
Minimum dimensions of 3 in.
F
G
Table 2—Minimum Free Area Of Combustion Air Opening
58ZAV
FURNACE
INPUT
(BTUH)
AIR FROM UNCON-
FINED INDOOR
SPACE
OUTDOOR AIR THROUGH
VERTICAL DUCTS
OUTDOOR AIR THROUGH
HORIZONTAL DUCTS
OUTDOOR AIR THROUGH
SINGLE DUCT
Free Area
of Opening
(Sq In.)
Free Area of
Opening and Duct
(Sq In.)
Round
Pipe
(In. Dia)
Free Area of
Opening and Duct
(Sq In.)
Round
Pipe
(In. Dia)
Free Area of
Opening and Duct
(Sq In.)
Round
Pipe
(In. Dia)
46,000 100 11.50 4 23.0 6 15.33 5
69,000 100 17.25 5 34.5 7 23.00 6
92,000 100 23.00 6 46.0 8 30.67 7
115,000 115 28.75 7 57.5 9 38.33 7
135,000 135 33.75 7 67.5 10 45.00 8
* Free area shall be equal to or greater than the sum of the areas of all vent connectors in the confined space. Opening area must be increased if other gas appliances
in the space require combustion air.
6