438335-UIM-C-1209
Johnson Controls Unitary Products
27
COMBUSTION AIR SUPPLY
All installations must comply with Section 5.3, Air for Combustion and
Ventilation of the National Fuel Gas Code, ANSI Z223.1 or Sections
7.2, 7.3 or 7.4 of CAN/CGA B149.1 or .2 Installation Code - latest edi-
tions.
This furnace is certified to be installed with one of three possible com-
bustion air intake configurations.
1.
OUTDOOR COMBUSTION AIR:
This is a direct vent configuration
where the combustion air is supplied through a PVC or ABS pipe
that is connected to the PVC coupling attached to the furnace and
is terminated in the same atmospheric zone as the vent. This type
of installation is approved on all models. Refer to Figure 35.
2.
AMBIENT COMBUSTION AIR:
Combustion air is supplied from
the area surrounding the furnace through openings in the furnace
casing. The combustion air and the vent pipes are not terminated
in the same atmospheric zone. Refer to Figure 30 for vent termina-
tions. Refer to "Ambient Combustion Air Supply" for proper instal-
lation. Refer to Figure 36.
3.
VENTILATED COMBUSTION AIR:
Combustion air is supplied
through a PVC or ABS pipe that is connected to the PVC coupling
attached to the burner box and is terminated in a ventilated attic or
crawl space. The combustion air and the vent pipes are not termi-
nated in the same atmospheric zone. Refer to Figure 38 for attic
and crawl space termination. Only the combustion air intake may
terminate in the attic. The vent must terminate outside.
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 35) 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 35) is the furnace
vent pipe.
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.”
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. It is
not piped directly into the furnace. A single, properly sized pipe from the
furnace vent connector to the outdoors must be provided. It is recom-
mended that the supplied intake coupling and 18” (46 cm) of pipe be
attached to the furnace to prevent accidental blockage of the combus-
tion air intake.
An
unconfined space
is not less than 50 cu.ft (1.42 m
3
) per 1,000 Btu/
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
3
) per 1,000
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 12, to estimate free area.
* 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.
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.
FIGURE 35:
Direct Vent Air Intake Connection and Vent Connection
NOTICE
Vent pipe cements
into socket just
above top panel
Or vent pipe may be
clamped into outlet
of drain coupling
Connects to
collar on top
of burner box
FIGURE 36:
Combustion Airflow Path Through The Furnace Casing
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.
Table 12:
Estimated Free Area
Wood or Metal
Louvers or Grilles
Wood 20-25%*
Metal 60-70% *
1/4” (6.4 mm)
mesh or larger 100%
Vent pipe cements
into socket just
above top panel
Or vent pipe may be
clamped into outlet
of drain coupling
COMBUSTION AIR
