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Winter Design
Termperature (
20
0
-20
‡ = Insulation thickness greater than 3/8 inch, based on an R value of
3.5 (ft*°F*hr)/(BTU*in)
Table 5 describes the maximum length of flue
pipe that can travel through an unconditioned
space or an exterior space. The total vent length
must not exceed the lengths noted on Table 5.
Vertical Venting
Figure 22 shows the proper installation and clear-
ances for vertical vent termination. The roof pen-
etration must be properly flashed and waterproofed
with a plumbing roof boot or equivalent flashing.
Termination spacing requirements from the roof and
from each other must be per Figure 22.
Vent and combustion air piping may be installed
in an existing chimney which is not in use
provided that:
a. Both the exhaust vent and air intake run
the length of the chimney.
b. The top of the chimney is sealed and
weatherproofed.
c. The termination clearances shown in
Figure 22 are maintained.
d. No other gas fired or fuel burning
appliances are vented through the
chimney.
Upflow Models
Roll-Out Limit
Shut-Off Valve
with 1/ 8" NPT
Plugged Tap
Burner
Assembly
Some Utilities
Require Shut-
Off Valve to
be 4 to 5 feet
Above Floor
Ground
Joint
Dripleg
Union
Automatic Gas Valve
(with manual shut-off)
24
Maximum Flue Pipe Length in
Unconditioned and Exterior Spaces
Without Insulation
(feet)
45
20
10
Table 5. Vent Protection
Burner Viewport
Denotes field-
provided and
installed
components.
Figure 24a. Typical Gas Service Connection
With Insulation
(feet)
70
70
60
Vent Freezing Protection
When the vent pipe is exposed to temperatures
below freezing, i.e., when it passes through
unheated spaces, chimneys, etc., the pipe must
be insulated with 1/2 inch thick sponge rubber
insulation, Armaflex-type insulation or equiva-
lent. Insulating pipe is important to avoid con-
densate icing.
For extremely cold climates or for conditions of
short furnace cycles (i.e. set back thermostat
conditions) the last three feet of vent pipe can be
reduced one nominal pipe size provided that the
total vent length is at least 15 feet in length and
the vent is sized in accordance with the venting
requirements (Table 4) before this reduction is
applied. (Example: 3" to 2-1/2") Smaller vent
pipes are less susceptible to freezing, but must
not be excessively restrictive.
Concentric Vent Termination
A concentric vent termination is approved for
use with these furnaces. The kit part number is
904176. For proper installation of the concentric
vent termination, follow the installation instruc-
tions provided with that kit.
Downflow Models
Denotes field-
Automatic
provided and
Gas Valve
installed
(with manual
components.
shut-off)
Ground Joint
Union
Roll-Out Limit
Burner
Assembly
Shut-Off Valve
with 1/ 8" NPT
Plugged Tap
Some Utilities
Require Shut-
Off Valve to
be 4 to 5 feet
Above Floor
Dripleg
Burner Viewport
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