
28
Inlet gas supply pressures must be maintained within
the ranges specified in the following table. The supply
pressure must be constant and available with all other
household gas fired appliances operating. The minimum
gas supply pressure must be maintained to prevent
unreliable ignition. The maximum must not be exceeded
to prevent unit overfiring.
T
O
AVOID
POSSIBLE
UNSATISFACTORY
OPERATION
OF
EQUIPMENT
DAMAGE
DUE
TO
UNDERFIRING
OR
EQUIPMENT
,
USE
THE
PROPER
SIZE
OF
NATURAL
/
PROPANE
GAS
PIPING
NEEDED
WHEN
RUNNING
PIPE
FROM
THE
METER
/
TANK
TO
THE
FURNACE
.
WARNING
HIGH ALTITUDE INSTALLATION
When this furnace is installed at high altitude, the
appropriate High Altitude Kit including orifices and a
pressure switch(s) must be installed. These changes are
necessary to compensate for the natural reduction in the
density of both the gas fuel and the combustion air at
higher altitude.
Installation of this furnace at altitudes above 7000 ft (2134
m), shall be made in accordance with the Listed High
Altitude Conversion Kit available with this furnace.
Do not de-rate the furnace by adjusting the manifold
pressure to a lower pressure than specified on the furnace
rating plate. The combination of the lower air density and
a lower manifold pressure will prohibit the burner orifice
from drawing the proper amount of air into the burner. This
may cause incomplete combustion, flashback, and yellow
tipping.
In some areas the gas supplier may artificially derate the
gas in an effort to compensate for the effects of altitude.
If the gas is artificially derated, the appropriate orifice size
must be determined based upon the BTU/ft³ content of
the derated gas and the altitude. Refer to the National
Fuel Gas Code, NFPA 54/ANSI Z223.1, and information
provided by the gas supplier to determine the proper
orifice size. A different pressure switch may be required
at high altitude regardless of the BTU/ft³ content of the
fuel used. Consult the furnace Specification Sheet. All
conversions must be performed by a qualified installer, or
service agency.
Propane Gas Conversion
This furnace is shipped from the factory configured for
natural gas at standard altitude. To operate this furnace
on L.P. gas, a LPM-07 LP Conversion kit must be used.
Propane gas installations require an orifice and spring
change to compensate for the energy content difference
between natural and propane gas.
Twinning
Two furnaces of the same model may be twinned. The
integrated control board has a 3/16” terminal labeled
“TWIN” located beside the low voltage thermostat
connection strip. Twinning allows simultaneous operation
of two furnaces and forces the indoor blower motors of
each furnace to operate synchronously into a common
duct system. Using the twinning function will require only
field installed wiring with no external kits or parts. The
staging and speed tap options must be set the same on
both furnaces.
NOTE: Each furnace must be connected to it’s own 115
VAC power supply. The L1 connection to each furnace
must be in phase (connected to circuit breakers on the
same 115 VAC service panel phase leg). To verify that
the furnaces are in phase, check from L1 to L1 on each
furnace with a voltmeter. If the furnaces are in phase,
the voltage between both furnaces will be ZERO.
ROOM THERMOSTAT
Y2
Y/Y1
C
G
R
W
Y2
Y/Y1
C
G
R
W
Y2
Y/Y1
C
G
R
W
TWIN
TWIN
COND UNIT
CONTACTOR
COND UNIT
CONTACTOR
FURNACE 1
FURNACE 2
Figure 36
T
O
PREVENT
UNRELIABLE
OPERATION
OR
EQUIPMENT
DAMAGE
,
THE
GAS
MANIFOLD
PRESSURE
MUST
BE
AS
SPECIFIED
ON
THE
UNIT
RATING
PLATE
. O
NLY
MINOR
ADJUSTMENTS
SHOULD
BE
MADE
BY
ADJUSTING
THE
GAS
VALVE
PRESSURE
REGULATOR
.
CAUTION
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
.
GAS SUPPLY AND PIPING
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
The furnace rating plate includes the approved furnace gas
input rating and gas types. The furnace must be equipped
to operate on the type of gas applied. This includes any
conversion kits required for alternate fuels and/or high
altitude.