Page 31
CAUTION
If this unit is being installed in an application with
combustion air coming in from a space serviced by
an exhaust fan, power exhaust fan, or other device
which may create a negative pressure in the space,
take care when sizing the inlet air opening. The
inlet air opening must be sized to accommodate the
maximum volume of exhausted air as well as the
maximum volume of combustion air required for all
gas appliances serviced by this space.
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Attic and Outlet Air to Outside)
NOTE
-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
2
per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
Ventilation Louvers
Inlet Air
(Minimum
12 in.(305mm) Above
attic floor)
Roof Terminated
Exhaust Pipe
Furnace
*Intake Debris
Screen
(Provided)
FIGURE 24
NOTE
-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
2
per 1.17kW) per
hour of the total input rating of all equipment in the enclosure.
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Crawlspace and Outlet Air to Outside)
Roof Terminated
Exhaust Pipe
Furnace
Ventilation
Louvers
(Crawl space)
*Intake Debris Screen Provided)
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
Coupling or
3 in. to 2 in.
Transition
(Field Provided)
FIGURE 25
General Guidelines for Vent Terminations
In Non-Direct Vent applications, combustion air is taken
from indoors or ventilated attic or crawlspace and the flue
gases are discharged to the outdoors. The ML296UHV is
then classified as a non-direct vent, Category IV gas fur
-
nace.
In Direct Vent applications, combustion air is taken from
outdoors and the flue gases are discharged to the out
-
doors.
The ML296UHV is then classified as a direct vent, Cate
-
gory IV gas furnace. In both Non-Direct Vent and Direct
Vent applications, the vent termination is limited by local
building codes. In the absence of local codes, refer to the
current National Fuel Gas Code ANSI Z223-1/NFPA 54 in
U.S.A., and current CSA-B149 Natural Gas and Propane
Installation Codes in Canada for details.
Position termination according to location given in FIG
URE 27 or FIGURE 28. In addition, position termination so
it is free from any obstructions and 12” above the average
snow accumulation.
At vent termination, care must be taken to maintain protec
-
tive coatings over building materials (prolonged exposure
to exhaust condensate can destroy protective coatings).
It is recommended that the exhaust outlet not be located
within 6 feet (1.8m) of an outdoor AC unit because the
condensate can damage the painted coating.
NOTE -
See TABLE 16 for maximum allowed exhaust
pipe length without insulation in unconditioned space
during winter design temperatures below 32°F (0°C). If re-
quired exhaust pipe should be insulated with 1/2” (13mm)
Armaflex or equivalent. In extreme cold climate areas,
3/4” (19mm) Armaflex or equivalent may be necessary.
Insulation must be protected from deterioration. Armaflex
with UV protection is permissible. Basements or other en-
closed areas that are not exposed to the outdoor ambient
temperature and are above 32 degrees F (0°C) are to be
considered conditioned spaces.
IMPORTANT
Do not use screens or perforated metal in exhaust
or intake terminations. Doing so will cause freeze-
ups and may block the terminations
.
IMPORTANT
For Canadian Installations Only:
In accordance to CSA International B149 installation
codes, the minimum allowed distance between the
combustion air intake inlet and the exhaust outlet
of other appliances shall not be less than 12 inches
(305mm).