General Guidelines For Vent Terminations - Lennox ML296UHV(X) Series Manual

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 in­
let 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)
Roof Terminated
Exhaust Pipe
* See table 15 for maximum vent lengths
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
hour of the total input rating of all equipment in the enclosure.
FIGURE 23
EQUIPMENT IN CONFINED SPACE
(Inlet Air from Ventilated Crawlspace and Outlet Air to Outside)
Roof Terminated
Exhaust Pipe
Ventilation
Furnace
Louvers
(Crawl space)
Coupling or
*Intake Debris Screen Provided)
3 in. to 2 in.
Transition
(Field Provided)
* See table 15 for maximum vent lengths
NOTE-The inlet and outlet air openings shall each have a free area
of at least one square inch per 4,000 Btu (645mm
hour of the total input rating of all equipment in the enclosure.
FIGURE 24
Ventilation Louvers
Inlet Air
(Minimum
12 in.(305mm) Above
attic floor)
*Intake Debris
Screen
(Provided)
Furnace
2
per 1.17kW) per
Inlet Air
(Minimum
12 in.(305mm)
Above crawl
space floor)
2
per 1.17kW) per

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,
Category 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 figure 26
or 27. In addition, position termination so it is free from any
obstructions and 12" above the average snow accumula­
tion.
At vent termination, care must be taken to maintain
protective 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 required
exhaust pipe should be insulated with 1/2" (13mm) Arma­
flex or equivalent. In extreme cold climate areas, 3/4"
(19mm) Armaflex or equivalent may be necessary. Insula­
tion must be protected from deterioration. Armaflex with
UV protection is permissable. 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.
Do not use screens or perforated metal in exhaust
terminations. Doing so will cause freeze-ups and
may block the terminations.
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).
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