17
Natural Gas
Minimum: 4.5" w.c.
Maximum: 10.0" w.c.
Propane Gas
Minimum: 11.0" w.c.
Maximum: 13.0" w.c.
INLET GAS SUPPLY PRESSURE
NOTE:
Adjusting the minimum supply pressure below the limits in
the above table could lead to unreliable ignition. Gas input to the
burners must not exceed the rated input shown on the rating plate.
Overfiring of the furnace can result in premature heat exchanger
failure. Gas pressures in excess of 13 inches water column can
also cause permanent damage to the gas valve.
At all altitudes, the manifold pressure must be within 0.3 inches
w.c. of that listed in the Specification Sheet applicable to your
model for the fuel used. At all altitudes and with either fuel, the air
temperature rise must be within the range listed on the furnace
nameplate. Should this appliance be converted to LP, refer to the
instructions included in the factory authorized LP conversion kit.
H
IGH
A
LTITUDE
D
ERATE
IMPORTANT NOTE:
The furnace, as shipped, requires no change to
run between 0 - 5500 feet. Do not attempt to increase the firing rate
by changing orifices or increasing the manifold pressure below
5500 feet. This can cause poor combustion and equipment failure.
High altitude installations above 5500 feet may require both a
pressure switch and an orifice change. These changes are neces-
sary to compensate for the natural reduction in the density of both
the gas fuel and the combustion air at higher altitude.
For installations above 5500 feet, please refer to your distributor
for required kit(s).
Contact the distributor for a tabular listing of appropriate
manufacturer’s kits for propane gas and/or high altitude installa-
tions. The indicated kits must be used to insure safe and proper
furnace operation. All conversions must be performed by a quali-
fied installer, or service agency.
P
ROPANE
G
AS
C
ONVERSION
WARNING
P
OSSIBLE
PROPERTY
DAMAGE
,
PERSONAL
INJURY
OR
DEATH
MAY
OCCUR
IF
THE
CORRECT
CONVERSION
KITS
ARE
NOT
INSTALLED
. T
HE
APPROPRIATE
KITS
MUST
BE
APPLIED
TO
ENSURE
SAFE
AND
PROPER
FURNACE
OPERATION
. A
LL
CONVERSIONS
MUST
BE
PERFORMED
BY
A
QUALIFIED
INSTALLER
OR
SERVICE
AGENCY
.
This unit is configured for natural gas. The appropriate
manufacturer’s propane gas conversion kit, must be applied for
propane gas installations. Refer to the “Propane Gas and/or High
Altitude Installations” section for details.
If converting to LP gas, it is recommended that an LPLP0* kit also
be installed. The use of this kit will prevent the furnace from firing
when the LP gas supply pressure is too low to support proper
combustion.
Models using Single Stage Gas Valves
Altitude
Gas
Kit
Orifice
Manifold
Pressure
Pressure
Sw itch
Propane
LPT-03
#55
10.0" w .c.
NOTE:
*MS81405DN** models utilize #43 orifices in Natural gas
applications.
0 - 5500
Natural
None
#45
3.5" w .c.
None
Models using 2-Stage Gas Valves
High
Stage
Low
Stage
Natural
None
#45
3.5" w .c.
1.9" w .c.
None
Propane
LPM-06
#55
10.0" w .c.
6.0" w .c.
None
0 - 5500
NOTE:
*MH81405DN** models utilize #43 orif ices in Natural gas
applications.
Gas
Altitude
Kit
Orifice
M anifold Pre s s ur e
Pre s s ure
Sw itch
Change
Contact your distributor for a tabular listing of appropriate
manufacturer’s kits for propane gas and/or high altitude installa-
tions. The indicated kits must be used to insure safe and proper
furnace operation. All conversions must be performed by a quali-
fied installer, or service agency.
G
AS
P
IPING
C
ONNECTIONS
T
O
AVOID
POSSIBLE
UNSATISFACTORY
OPERATION
PMENT
,
USE
THE
PROPER
SIZE
OF
NATURAL
/
PROPANE
GAS
PIPING
NEEDED
WHEN
RUNNING
PIPE
FROM
THE
METER
/
TANK
TO
THE
FURNACE
.
OR
EQUIPMENT
DAMAGE
DUE
TO
UNDERFIRING
OF
EQUI
WARNING
When sizing gas lines, be sure to include all appliances which will
operate simultaneously.
The gas piping supplying the furnace must be properly sized based
on the gas flow required, specific gravity of the gas, and length of
the run. The gas line installation must comply with local codes, or
in their absence, with the latest edition of the National Fuel Gas
Code, NFPA 54/ANSI Z223.1.
