507281-06
Page 25 of 58
Issue 1724
Figure 31.
Equipment in Confined Space
(Inlet Air from Ventilated Crawlspace 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.
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)
* See Maximum Vent Lengths table
General Guidelines for Vent Terminations
In Non–Direct Vent applications, combustion air is taken
from indoors and the flue gases are discharged to the
outdoors. This furnace is then classified as a non–direct
vent, Category IV gas furnace.
In Direct Vent applications, combustion air is taken from
outdoors and the flue gases are discharged to the outdoors.
The furnace 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
33 and Figure 44. 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
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 (1.8 m) of a condensing unit because
the condensate can damage the painted coating.
NOTE
:
See Table 6 for maximum allowed exhaust pipe
length without insulation in unconditioned space during
winter design temperature below 32° F (0° C). If required,
exhaust pipe should be insulated with 1/2” (13 mm),
Armaflex or equivalent when run through an unconditional
area. In extremely cold climate areas with temperature
below 20° F (6.7° C), it is recommended that 3/4” (19 mm)
Armaflex or equivalent be used. Insulation on outside
runs of exhaust pipe should be painted or wrapped to
protect insulation from deterioration in accordance with
the insulation manufacturers recommendation. Exhaust
pipe insulation may not be necessary in some specific
applications.
NOTE
:
During extremely cold temperatures, below
approximately 20° F (6.7° C), units with long runs of vent
pipe through unconditioned space, even when insulated,
may form ice in the exhaust termination that prevents the
unit from operating properly. Longer run times of at least 5
minutes will alleviate most icing problems. Also, a heating
cable may be installed on exhaust piping and termination
to prevent freeze-ups. Heating cable installation kits are
available. See unit specification sheets for part numbers.
Do not use screens or perforated metal in exhaust
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 (305
mm).
IMPORTANT
