364861-UIM-D-1209
Johnson Controls Unitary Products
27
An
unconfined space
is not less than 50 cu.ft (1.42 m
3
) per 1,000 Btu/
hr (0.293 kW/h) 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 (0.293 kW/h) 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 Table11, 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.
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.
Air Supply Openings and Ducts
1.
An opening may be used in lieu of a duct to provide to provide the
outside air supply to an appliance unless otherwise permitted by
the authority having jurisdiction. The opening shall be located
within 12” (30.5 cm) horizontally from, the burner level of the appli-
ance. Refer to “AIR SOURCE FROM OUTDOORS AND VENT
AND SUPPLY AIR SAFETY CHECK” in these instructions for
additional information and safety check procedure.
2.
The duct shall be either metal, or a material meeting the class 1
requirements of CAN4-S110 Standard for Air Ducts.
3.
The duct shall be least the same cross-sectional area as the free
area of the air supply inlet opening to which it connects.
4.
The duct shall terminate within 12” (30.5 cm) above, and within
24” (61 cm) horizontally from, the burner level of the appliance
having the largest input.
5.
A square or rectangular shaped duct shall only be used when the
required free area of the supply opening is 9 in
2
(58.06 cm
2
) or
larger. When a square or rectangular duct is used, its small dimen-
sion shall not be less than 3” (7.6 cm).
6.
An air inlet supply from outdoors shall be equipped with a means
to prevent the direct entry of rain and wind. Such means shall not
reduce the required free area of the air supply opening.
7.
An air supply inlet opening from the outdoors shall be located not
less than 12” (30.5 cm) above the outside grade level.
Table 11:
Estimated Free Area
Wood or Metal
Louvers or Grilles
Wood 20-25%*
Metal 60-70% *
1/4” (6.4 mm)
mesh or larger 100%
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
BTUH Input Rating
Minimum Free Area
Required for Each Opening
40,000
40 in
2
(258 cm
2
)
60,000
60 in
2
(387 cm
2
)
80,000
80 in
2
(516 cm
2
)
100,000
100 in
2
(645 cm
2
)
120,000
120 in
2
(742 cm
2
)
130,000
130 in
2
(838 cm
2
)
Table 13:
Free Area
BTUH Input
Rating
Minimum Free Area Required for Each Opening
Horizontal Duct
(2,000 BTUH)
Vertical Duct or
Opening to Outside
(4,000 BTUH)
Round Duct
(4,000 BTUH)
40,000
20 in
2
(129 cm
2
)
10 in
2
(64 cm
2
)
4” (10 cm)
60,000
30 in
2
(193 cm
2
)
15 in
2
(97 cm
2
)
5” (13 cm)
80,000
40 in
2
(258 cm
2
)
20 in
2
(129 cm
2
)
5” (13 cm)
100,000
50 in
2
(322 cm
2
)
25 in
2
(161 cm
2
)
6” (15 cm)
120,000
60 in
2
(387 cm
2
)
30 in
2
(193 cm
2
)
7” (18 cm)
130,000
65 in
2
(419 cm
2
)
33 in
2
(213 cm
2
)
7” (18 cm)
EXAMPLE: Determining Free Area.
Appliance
1 Appliance
2 Total Input
100,000
+ 30,000 = (130,000
4,000) = 32.5 Sq. In. Vertical
Appliance
1 Appliance
2 Total Input
100,000
+ 30,000 = (130,000
2,000) = 65 Sq. In. Horizontal
FIGURE 38:
Outside and Ambient Combustion Air
Gable
Vent
Gas
Vent
Soffit
Vent
Ventilated
Attic
Top Above
Insulation
Optional
Inlet (a)
Outlet
Air (a)
Ventilated
Crawl Space
Gas
Water
Heater
Furnace
Soffit
Vent
Gas
Water
Heater
Inlet
Air (a)
Inlet
Air (b)
Furnace
Gas
Vent
Outlet
Air (a)
Outlet
Air (b)
Inlet
Air (a)
Inlet
Air (b)
Gas
Water
Heater
Furnace
Ventilated
Attic
Top Above
Insulation
Gable
Vent
Gas
Vent
