21
Figure 29
LP Gas
Configuration
Black Cover
Red
Natural Gas
Configuration
Figure 29. Robertshaw Gas Valve
This furnace is shipped from the factory with orifices and
gas regulator settings for natural gas operation at sea
level altitudes. At 2000 feet, the NFGC requires that this
appliance be derated 4% for each 1000 feet of altitude. For
example, the input needs to be reduced 8% at 2,000 feet,
12% at 3,000 feet and etc. This deration is in reference
to the input rate and gas heating value at sea level. See
Flue Gas sampling
It may be necessary to take flue gas sampling from oil
and gas furnaces (M5S and M1B Series Models) in order
to check the performance after furnace installation. A
flue gas sample may be taken from the heat exchanger,
which is located behind the hole of the top-front of blower
compartment.
1. Turn off all electric power to the appliance.
2. Remove the black plastic cap located above the blower.
Do not discard cap.
3. Drill a hole through the top of the blower compartment.
notE:
Hole diameter should be same size as sampling
tube.
4. Insert sampling tube through the drilled hole and into
the heat exchanger.
5. After a complete check and adjustment of furnace
performance, seal the drilled hole with a screw larger
than the hole.
notE:
Seal the screw threads with silicon
sealant - rated at least 500° F.
6. Plug the outside hole with the plastic cap removed in
step 3.
Figure 28
Figure 28. Honeywell Gas Valve
PRESSURE
REGULATOR
CAP
M11678
N
AT N
AT
L
P
L
P
N
AT N
AT
OR
OTHER SIDE
OF CAP
INLET PRESSURE
TAP (1/8 NPT)
OUTLET PRESSURE
TAP (1/8 NPT)
