Instructions / Assembly

20
HIGH ALTITUDE 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
necessary to compensate for the natural reduction in the den-
sity of both the gas fuel and the combustion air at higher alti-
tude.
For installations above 5500 feet, please refer to your distribu-
tor for required kit(s).
Contact the distributor for a tabular listing of appropriate
manufacturer’s kits for propane gas and/or high altitude instal-
lations. The indicated kits must be used to insure safe and
proper furnace operation. All conversions must be performed
by a qualified installer, or service agency.
PROPANE 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 sup-
port 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:
*
M
S
81405DN
**
models utilize
#
43 ori
f
ices 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 orifices in Natural gas
applications.
Gas Altitude Kit Orifice
Manifold Pressure
Pressure
Sw itch
Change
Contact your distributor for a tabular listing of appropriate
manufacturer’s kits for propane gas and/or high altitude instal-
lations. The indicated kits must be used to insure safe and
proper furnace operation. All conversions must be performed
by a qualified installer, or service agency.
GAS PIPING 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 a trunk line, 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.
Natural Gas Capacity of Pipe
In Cubic Feet of Gas Per Hour (CFH)
Length of Nominal Black Pipe Size
Pipe in Feet 1/2" 3/4" 1" 1 1/4" 1 1/2"
10 132 278 520 1050 1600
20 92 190 350 730 1100
30 73 152 285 590 980
40 63 130 245 500 760
50 56 115 215 440 670
60 50 105 195 400 610
70 46 96 180 370 560
80 43 90 170 350 530
90 40 84 160 320 490
100 38 79 150 305 460
(Pressure 0.5 psig or less and pressure drop of 0.3" W.C.; Based on
0.60 Specific Gravity Gas)
CFH =
BTUH Furnace Input
Heating Value of Gas (BTU/Cubic Foot)
To connect the furnace to the building’s gas piping, the installer
must supply a ground joint union, drip leg, manual shutoff valve,
and line and fittings to connect to gas valve. In some cases,
the installer may also need to supply a transition piece from 1/
2" pipe to a larger pipe size.
The following stipulations apply when connecting gas piping.
• Use black iron or steel pipe and fittings for the building
piping.