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5594752-UIM-B-0419
COMBUSTION
AIR
FIGURE 15: Combustion Airflow Path Through The Furnace Casing to
the Burner Compartment
WARNING
!
This type of installation requires that the supply air to the appliance(s)
be of a sufficient amount to support all of the appliance(s) in the area.
Operation of a mechanical exhaust, such as an exhaust fan, kitchen
ventilation system, clothes dryer or fireplace may create conditions
requiring special attention to avoid unsatisfactory operation of gas
appliances. A venting problem or a lack of supply air will result in a
hazardous condition, which can cause the appliance to soot and gen-
erate dangerous levels of CARBON MONOXIDE, which can lead to
serious injury, property damage and / or death.
An unconfined space is not less than 50 cu.ft (1.42 m
hr (0.2928 kW) input rating for all of the appliances installed in that
area.
Rooms communicating directly with the space containing the appli-
ances are considered part of the unconfined space, if doors are fur-
nished with openings or louvers.
A confined space is an area with less than 50 cu.ft (1.42 m
Btu/hr (0.2928 kW) input rating for all of the appliances installed in that
area. The following must be considered to obtain proper air for combus-
tion and ventilation in confined spaces.
Combustion Air Source From Outdoors
The blocking effects of louvers, grilles and screens must be given con-
sideration in calculating free area. If the free area of a specific louver or
grille is not known, refer to Table 6, to estimate free area.
Table 6: Estimated Free Area
Wood or Metal
Louvers or Grilles
Screens+
* Do not use less than 1/4" (6.4 mm) mesh
+ Free area of louvers and grille varies widely; the installer should follow
louver or grille manufacturer's instructions.
14
3
) per 1,000 Btu/
3
) per 1,000
Wood 20-25%*
Metal 60-70% *
1/4" (0.635 cm)
mesh or larger 100%
Dampers, Louvers and Grilles (Canada Only)
1. The free area of a supply air opening shall be calculated by sub-
tracting the blockage area of all fixed louvers grilles or screens from
the gross area of the opening.
2. Apertures in a fixed louver, a grille, or screen shall have no dimen-
sion smaller than 1/4" (6.4 mm).
3. A manually operated damper or manually adjustable louvers are
not permitted for use.
4. A automatically operated damper or automatically adjustable lou-
vers shall be interlocked so that the main burner cannot operate
unless either the damper or the louver is in the fully open position.
WARNING
!
When a Category I furnace is removed or replaced, the original vent-
ing system may no longer be correctly sized to properly vent the
attached appliances.
An improperly sized vent system can cause CARBON MONOXIDE to
spill into the living space causing personal injury, and or death.
Table 7: Unconfined Space Minimum Area
BTUH Input Rating
40,000
60,000
80,000
100,000
120,000
130,000
Table 8: Free Area
Minimum Free Area Required for Each Opening
BTUH Input
Horizontal Duct
Rating
(2,000 BTUH)
2
40,000
20 in
(129 cm
2
60,000
30 in
(193 cm
2
80,000
40 in
(258 cm
2
100,000
50 in
(322 cm
2
120,000
60 in
(387 cm
2
130,000
65 in
(419 cm
EXAMPLE: Determining Free Area.
Appliance
1 Appliance
+ 30,000 = (130,000 4,000) = 32.5 Sq. In. Vertical
100,000
Appliance
1 Appliance
+ 30,000 = (130,000 2,000) = 65 Sq. In. Horizontal
100,000
Minimum Free Area
Required for Each Opening
2
2
40 in
(258 cm
)
2
2
60 in
(387 cm
)
2
2
80 in
(516 cm
)
2
2
100 in
(645 cm
)
2
2
120 in
(742 cm
)
2
2
130 in
(838 cm
)
Vertical Duct or
Round Duct
Opening to Outside
(4,000 BTUH)
(4,000 BTUH)
2
2
2
4" (10 cm)
)
10 in
(64 cm
)
2
2
2
5" (13 cm)
)
15 in
(97 cm
)
2
2
2
5" (13 cm)
)
20 in
(129 cm
)
2
2
2
6" (15 cm)
)
25 in
(161 cm
)
2
2
2
7" (18 cm)
)
30 in
(193 cm
)
2
2
2
7" (18 cm)
)
33 in
(213 cm
)
2 Total Input
2 Total Input
Johnson Controls Ducted Systems
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