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FAN-ASSISTED COMBUSTION SYSTEM
This appliance is equipped with an integral mechanical means to draw
products of combustion through the heat exchanger.
Ambient Combustion Air Supply
This type installation will draw the air required for combustion from
within the space surrounding the appliance and from areas or rooms
adjacent to the space surrounding the appliance. This may be from
within the space in a non-confined location or it may be brought into the
furnace area from outdoors through permanent openings or ducts. A
single, properly sized pipe from the furnace vent connector to the out-
doors must be provided. For upflow models combustion air is brought
into the furnace through the unit top panel opening.
COMBUSTION AIR
FIGURE 28: Combustion Airflow Path Through The Furnace Casing to
the Burner Compartment
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 openings 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.
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 7, to estimate free area.
Table 7: Estimated Free Area
Louvers or Grilles
* 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.
Dampers, Louvers and Grilles (Canada Only)
1. The free area of a supply air opening shall be calculated by subtract-
ing 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 0.25" (0.64 cm).
3. A manually operated damper or manually adjustable louvers are not
permitted for use.
4. A automatically operated damper or automatically adjustable louvers
shall be interlocked so that the main burner cannot operate unless
either the damper or the louver is in the fully open position.
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 8: Unconfined Space Minimum Area
BTUH Input Rating
60,000
80,000
100,000
120,000
3
) per 1,000 Btu/
Table 9: Free Area
BTUH Input
Rating
60,000
3
) per 1,000
80,000
100,000
120,000
EXAMPLE: Determining Free Area.
Appliance
100,000
Appliance
100,000
Wood or Metal
Screens+
Minimum Free Area
Required for Each Opening
60 in
80 in
100 in
120 in
Minimum Free Area Required for Each Opening
Vertical Duct or
Horizontal Duct
Opening to Outside
(2,000 BTUH)
(4,000 BTUH)
2
2
30 in
(193 cm
)
15 in
2
2
40 in
(258 cm
)
20 in
2
2
50 in
(322 cm
)
25 in
2
2
60 in
(387 cm
)
30 in
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
987158-UIM-B-1013
Wood 20-25%*
Metal 60-70% *
1/4" (0.635 cm)
mesh or larger 100%
2
2
(387 cm
)
2
2
(516 cm
)
2
2
(645 cm
)
2
2
(742 cm
)
Round Duct
(4,000 BTUH)
2
2
5" (13 cm)
(97 cm
)
2
2
5" (13 cm)
(129 cm
)
2
2
6" (15 cm)
(161 cm
)
2
2
7" (18 cm)
(193 cm
)
2 Total Input
2 Total Input
21
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