Gas Supply And Piping; General; H A D; High Altitude Derate - Goodman GMS8 Installation & Operating Instructions Manual

circulation blowers of the two furnaces. Furnaces must be same
model and heat / cool speeds the same. In addition, both
furnaces must be powered by separate circuits originating from
the same power leg in the main electrical box (hot and neutral
must be in phase). Furnaces can be twinned to provide either
single or 2-stage heat. If used as 2-stage heat the temperature
rise from the register to return will be reduced during low fire
operation.
To twin furnaces, ensure models are the same. Connect twin
terminals on both furnaces and ensure heat and cool speeds
are the same on both furnaces. For single stage operation, wire
thermostat as normal to one of the furnaces. Conncect W from
furnace 1 to one of the coil terminals on an isolation relay.
Connect the other coil terminal to C of furnace 1. Connect R of
furnace 2 to the common terminal of the isolation relay. Connect
normally open (NO) to W of furnace 2.
For 2-stage operation connect twin of both furnaces. Connect
one furnace to 2-stage thermostat as normal, connecting W1 on
thermostat to W on this furnace. Connect W2 from thermostat to
the coil terminal on isolation relay. Connect the other coil terminal
to C of furnace 1. Connect common of the isolation relay to R on
furnace 2 and normally open (NO) to W of furnace 2.
stage configuration, furnace 1 will provide low stage heat
(circulator blower of furnace 2 will run at heat speed). During a
call for High heat both furnaces will operate.
NOTE: Check operation of twin by turning thermostat to "fan on"
or placing a jumper wire from R to G (furnace connected to
thermostat). If twinning wire is working properly, both blowers
will turn on at the same speed. If twinning does not work properly,
check proper 24-volt polarity and ensure both furnaces are
powered from the same power leg. If the 24-volt polarity is
incorrect, switch common and 24-volt leads on furnace that is
not working. Check operation.
Furnace 1
TWIN Y W R G C
Thermostat
With 2-
Furnace 2
TWIN Y W R G C
NO
C
Isolation Relay
Furnace 1
TWIN Y W R G
R
Y
2-Stage Thermostat
IX. GAS SUPPLY AND PIPING
G
ENERAL
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.
T
O PREVENT UNRELIABLE OPERATION OR EQUIPMENT DAMAGE, THE INLET
GAS SUPPLY PRESSURE MUST BE AS SPECIFIED ON THE UNIT RATING PLATE
WITH ALL OTHER HOUSEHOLD GAS FIRED APPLIANCES OPERATING.
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.
Inlet Gas Supply Pressure
Natural Gas
Minimum: 5.0" w.c.
Propane Gas Minimum: 11.0" w.c.
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 Product Data Book 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
LPT* .
H A D
IGH LTITUDE ERATE
IMPORTANT NOTE: The furnace will naturally derate itself with
altitude. Do not attempt to increase the firing rate by changing
orifices or increasing the manifold pressure. This can cause
poor combustion and equipment failure.
When this furnace is installed at high altitude, the appropriate
High Altitude orifice kit must be applied. The furnace is supplied
with orifices sized for natural gas at altitudes up to 4,500 feet
17
Furnace 2
TWIN Y W R G
C
NO
C
Isolation Relay
W
W2
G
CAUTION
Maximum:10.0" w.c.
Maximum:13.0" w.c.
C