Direct Vent Air Intake Connection And Vent Connection; Estimated Free Area; Unconfined Space Minimum Area In Square Inch; Free Area - Johnson Controls MG9S*MP Installation Manual

Outdoor Combustion Air
Combustion Air Intake/Vent Connections
This installation requires combustion air to be brought in from outdoors.
This requires a properly sized pipe (Shown in Figure 30) that will bring
air in from the outdoors to the furnace combustion air intake collar on
the burner box. The second pipe (Shown in Figure 30) is the furnace
vent pipe.
NOTICE
An optional plastic birdscreen is shipped in the loose parts bag with
every furnace. This may be installed in the intake collar to prevent
any small objects from entering the furnace.
Connects to
collar on top
of burner box
FIGURE 30: Direct Vent Air Intake Connection and Vent Connection
The combustion air intake pipe should be located either through the
wall (horizontal or side vent) or through the roof (vertical vent). Care
should be taken to locate side vented systems where trees or shrubs
will not block or restrict supply air from entering the terminal.
Also, the terminal assembly should be located as far as possible from a
swimming pool or a location where swimming pool chemicals might be
stored. Be sure the terminal assembly follows the outdoor clearances
listed in Section #1 "Outdoor Air Contaminants."
This type of installation requires that the supply air to the appli-
ance(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 cre-
ate 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 appli-
ance to soot and generate dangerous levels of CARBON MONOX-
IDE, 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 openings are fur-
nished with doors.
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.
Johnson Controls Unitary Products
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 11, to estimate free area.
Table 11: Estimated Free Area
Dampers, Louvers and Grilles (Canada Only)
1.
Vent pipe cements
into socket just
above top panel
2.
Or vent pipe may be
3.
clamped into outlet
of drain coupling
4.
When a Category I furnace is removed or replaced, the original
venting 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 12: Unconfined Space Minimum Area in Square Inch
BTUH Input Rating
Table 13: Free Area
BTUH Input
3
) per 1,000 Btu/
EXAMPLE: Determining Free Area.
Appliance
100,000
Appliance
100,000
3
) per 1,000
Wood or Metal
Louvers or Grilles
Screens+
* Do not use less than 1/4"(0.635 cm) mesh
+ Free area of louvers and grille varies widely; the installer should follow
louver or grille manufacturer's instructions.
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.
Apertures in a fixed louver, a grille, or screen shall have no dimen-
sion smaller than 0.25" (0.64 cm).
A manually operated damper or manually adjustable louvers are
not permitted for use.
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.
Minimum Free Area in Square Feet
Required for Each Opening
60,000
80,000
100,000
120,000
Minimum Free Area Required for Each Opening
Horizontal Duct
Rating
(2,000 BTUH)
2 2
60,000
30 in (193 cm )
2 2
80,000
40 in (258 cm )
2 2
100,000
50 in (322 cm )
2 2
120,000
60 in (387 cm )
1 Appliance
+ 30,000 = (130,000  4,000) = 32.5 Sq. In. Vertical
1 Appliance
+ 30,000 = (130,000  2,000) = 65 Sq. In. Horizontal
420705-UIM-C-0310
Wood 20-25%*
Metal 60-70% *
1/4" (0.635 cm)
mesh or larger 100%
2 2
60 in (387 cm )
2 2
80 in (516 cm )
2 2
100 in (645 cm )
2 2
120 in (742 cm )
Vertical Duct or
Round Duct
Opening to Outside
(4,000 BTUH)
(4,000 BTUH)
2 2
5" (13 cm)
15 in (97 cm )
2 2
5" (13 cm)
20 in (129 cm )
2 2
6" (15 cm)
25 in (161 cm )
2 2
7" (18 cm)
30 in (193 cm )
2 Total Input
2 Total Input
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