268894-UIM-A-0407
Unitary Products Group
17
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 openings are not
furnished with doors.
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 9, to estimate free area.
+
Do not use less than 1/4” (0.635 cm) mesh
*
Free area or 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, 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.
An 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.
FIGURE 20:
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.
FIGURE 21:
Alternate Air Intake, Air Outlet and Chimney Connections
COMBUSTION AIR
COMBUSTION AIR
ATTACH VENT PIPE
DIRECTLY TO THE
SUPPLIED 4” FLUE
CONNECTOR
WITH 2 SCREWS
FURNACE
W
A
TER
HEA
TER
OUTLET
AIR
VENTILATION LOUVERS
(each end of attic)
CHIMNEY OR
GAS VENT
INLET
AIR
ALTERNATE
AIR INLET
VENTILATION LOUVERS FOR UNHEATED CRAWL SPACE
FIGURE 22:
Air Inlet, Outlet and Chimney Connections
TABLE 9:
Estimated Free Area
Wood or Metal
Louvers or Grilles
Wood 20-25%*
Metal 60-70% *
1/4” (0.635 cm)
mesh or larger 100%
FIGURE 23:
Typical Chimney Connections
FURNACE
W
A
TER
HEA
TER
OUTLET
AIR
VENTILATION LOUVERS
(each end of attic)
CHIMNEY OR
GAS VENT
INLET AIR DUCT
[ends 1 ft (30 cm)
above floor]
FURNACE
W
A
TER
HEA
TER
CHIMNEY OR
GAS VENT
OPENING
OPENING
