5532522-UIM-B-0619
12
Johnson Controls Ducted Systems
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 5, 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 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 appliance. Refer to
“COMBUSTION AIR SOURCE FROM OUTDOORS and VENT
AND SUPPLY AIR SAFETY CHECK” in these instructions for addi-
tional 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.
Combustion Air Source from Outdoors
1. Two permanent openings, one within 12” (30.5 mm) of the top and
one within 12” (30.5 mm) of the bottom of the confined space, shall
communicate directly or by means of ducts with the outdoors, crawl
spaces or attic spaces.
2. One permanent opening, commencing within 12” (30.5 cm) of the
top of the enclosure, shall be permitted where the equipment has
clearances of at least 1” (2.54 cm) from the sides and back and 6”
(15.24 cm) from the front of the appliance. The opening shall com-
municate directly with the outdoors and shall have a minimum free
area of:
a. 1 square in per 3000 Btu per hour (6.45 cm
3
per 0.879 kW) of the
total input rating of all equipment located in the enclosure.
b. Not less than the sum of all vent connectors in the confined
space.
Table 5:
Estimated Free Area
Wood or Metal
Louvers or Grilles
Wood 20-25%*
Metal 60-70% *
1/4” (0.635 cm)
mesh or larger 100%
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 6:
Unconfined Space Minimum Area
BTUH Input Rating
Minimum Free Area
Required for Each Opening
60,000
60 in
2
(387 cm
2
)
80,000
80 in
2
(516 cm
2
)
100,000
100 in
2
(645 cm
2
)
Table 7:
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)
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)
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 16:
Outside and Ambient Combustion Air
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