271001-UIM-A-0407
Unitary Products Group
9
IMPORTANT:
An accessible manual shutoff valve must be installed
upstream of the furnace gas controls and within 6 feet (1.8 m) of the fur-
nace.
The furnace must be isolated from the gas supply piping system by
closing its individual external manual shutoff valve during any pressure
testing of the gas supply piping system at pressures equal to or less
than 1/2 psig (3.5 kPa).
Gas piping may be connected from either side of the furnace using any
of the gas pipe entry knockouts on both sides of the furnace. Refer to
Figure 1 dimensions.
GAS ORIFICE CONVERSION FOR PROPANE (LP)
This furnace is constructed at the factory for natural gas-fired operation,
but may be converted to operate on propane (LP) gas by using a fac-
tory-supplied LP conversion kit. Follow the instructions supplied with
the LP kit. Refer to Table 6 or the instructions in the propane (LP) con-
version kit for the proper gas orifice size.
HIGH ALTITUDE GAS ORIFICE CONVERSION
This furnace is constructed at the factory for natural gas-fired operation
at 0 – 8,000 feet (0-m – 2,438 m) above sea level.
The manifold pressure must be changed in order to maintain proper
and safe operation when the furnace is installed in a location where the
altitude is greater than 8,000 feet (2,438 m) above sea level. Refer to
Tables 6 and 7 for proper manifold pressure settings.
HIGH ALTITUDE PRESSURE SWITCH CONVERSION
For installation where the altitude is less than 8,000 feet (2,438 m), it is
not required that the pressure switch be changed. For altitudes above
8,000 feet (2,438 m), see Table 17 Field Installed Accessories - High
Altitude Pressure Switch
FIGURE 7:
Horizontal Gas Piping
The gas valve body is a very thin casting that cannot take any
external pressure. Never apply a pipe wrench to the body of the gas
valve when installing piping. A wrench must be placed on the octag-
onal hub located on the gas inlet side of the valve. Placing a wrench
to the body of the gas valve will damage the valve causing improper
operation and/or the valve to leak.
MANUAL
SHUT-OFF
VALVE
GAS
PIPE
GAS
PIPE
DRIP
LEG
MANUAL
SHUT-OFF VALVE
GAS VALVE
GAS BURNERS
DRIP
LEG
LoNOx furnaces requiring propane (LP) gas must have the LoNOx
screens removed prior to installation and operation. See the
instructions supplied with the propane conversion kit or the start up
procedure at the back of these instructions on proper removal of the
NOx screens.
TABLE 6:
Nominal Manifold Pressure - High Fire
Single/Second Stage Manifold Pressures (in wc)
Single/Second Stage Manifold Pressures (kpa)
Altitude (feet)
Altitude (m)
0-7999
8000-8999
9000-9999
0-2437
2438-2742
2743-3048
Ga
s He
at
in
g V
a
lu
e
(B
TU/c
u f
t.)
800
3.5
3.5
3.5
Ga
s He
at
in
g V
a
lu
e
(MJ
/cu m)
29.8
0.87
0.87
0.87
850
3.5
3.5
3.5
31.7
0.87
0.87
0.87
900
3.5
3.5
3.5
33.5
0.87
0.87
0.87
950
3.5
3.5
3.3
35.4
0.87
0.87
0.81
1000
3.5
3.2
2.9
37.3
0.87
0.80
0.73
1050
3.5
2.9
2.7
39.1
0.87
0.73
0.67
1100
3.2
2.7
2.4
41.0
0.80
0.66
0.61
2500 (LP)
9.8
8.2
7.5
93.2 (LP)
2.44
2.03
1.86
TABLE 7:
Nominal Manifold Pressure - Low Fire
First Stage Manifold Pressures (in wc)
First Stage Manifold Pressures (kpa)
Altitude (feet)
Altitude (m)
0-7999
8000-8999
9000-9999
0-2437
2438-2742
2743-3048
Ga
s Hea
tin
g V
a
lue
(B
T
U
/c
u
f
t.)
800
1.7
1.7
1.7
Ga
s Hea
tin
g V
a
lue
(M
J/
cu
m)
29.8
0.42
0.42
0.42
850
1.7
1.7
1.7
31.7
0.42
0.42
0.42
900
1.7
1.7
1.7
33.5
0.42
0.42
0.42
950
1.7
1.7
1.5
35.4
0.42
0.42
0.38
1000
1.6
1.5
1.4
37.3
0.41
0.37
0.34
1050
1.5
1.4
1.3
39.1
0.37
0.34
0.31
1100
1.3
1.2
1.1
41.0
0.34
0.31
0.28
2500 (LP)
4.1
3.8
3.5
93.2 (LP)
1.03
0.95
0.87
