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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 0.25 in. (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 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.
WARNING
!
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.
FIGURE 29: Outside and Ambient Combustion Air
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 in. (30.5
cm) horizontally from the burner level of the appliance. 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 at 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 in. (30.5 cm) above, and within
24 in. (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
larger. When a square or rectangular duct is used, its small dimen-
sion shall not be less than 3 in. (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 in. (30.5 cm) above the outside grade level.
Johnson Controls Ducted Systems
Table 12: Unconfined Space Minimum Area in Square Inch
BTUH Input Rating
60,000
80,000
100,000
Table 13: Free Area
BTUH Input
Rating
60,000
80,000
100,000
EXAMPLE: Determining Free Area
Appliance
100,000
Appliance
100,000
Combustion Air Source from Outdoors
1. Two permanent openings, one within 12 in. (30.5 mm) of the top
and one within 12 in. (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 in. (30.5 mm) of the
top of the enclosure shall be permitted where the equipment has
clearances of at least 1 in. (2.54 cm) from the sides and back and 6
in. (15.24 cm) from the front of the appliance. The opening shall
communicate directly with the outdoors and shall have a minimum
free area of:
a.
b.
3. The duct shall be at least the same cross-sectional area as the free
2
2
(58.06 cm
) or
area of the air supply inlet opening to which it connects.
4. The blocking effects of louvers, grilles and screens must be given
consideration in calculating free area. If the free area of a specific
louver or grille is not known, see Table 11.
Minimum Free Area in Square Feet
Required for Each Opening
60 in
80 in
100 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
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
2
1 in
per 3000 Btu per hour (6.45 cm
total input rating of all equipment located in the enclosure
Not less than the sum of all vent connectors in the confined
space
5715184-BIM-A-0519
2
2
(387 cm
)
2
2
(516 cm
)
2
2
(645 cm
)
Round Duct
(4,000 BTUH)
2
2
5 in. (13 cm)
(97 cm
)
2
2
5 in. (13 cm)
(129 cm
)
2
2
6 in. (15 cm)
(161 cm
)
2 Total Input
2 Total Input
3
per 0.879 kW) of the
23
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