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LP GAS ORIFICE SELECTION
For LP Orifice selection, refer to the "LP Conversion" sec-
E. Order Orifices:
tion of this manual.
If a change in orifice size is required, they can be or-
dered from the local distributor. Orifice sizes are se-
lected by adding the 2-digit drill size required in the
orifice part number. Drill sizes available are 39 through
64. Metric sizes are available in 1.10mm (-90):
To order an orifice, use this format: Part number = 62-
22175-(drill size)
Example 1:
#60 drill size orifice required
Select Part # 62-22175-60
Example 2:
1.10 mm drill size orifice required
STEP 2: ADJUSTING THE GAS
Select Part # 62-22175-90
PRESSURES
The maximum gas supply pressure to the furnace
must not exceed 10.5" w.c. natural gas, or 13" w.c. LP
gas. The minimum supply gas pressure to the gas valve
should be 5" w.c. natural gas or 11" w.c. LP gas. A prop-
TABLE 14
NATURAL GAS ORIFICE SELECTION BASED ON HEATING VALUE AND ELEVATION (FOR U.S. & CANADA.)
erly calibrated manometer is required for accurate gas
pres sure measurements.
If the supply gas line pressure is above these ranges, in -
stall an in-line gas regulator to the furnace for natural gas
units. With LP gas, have the LP supplier reduce the line
pressure at the regulator.
If supply gas line pressure is below these ranges, either
remove any restrictions in the gas supply piping or enlarge
the gas pipe. See Tables 11 and 12 in Gas Supply section
of this manual. With LP gas, have the LP supplier adjust
the line pressure at the regulator.
ELEVATIONS ABOVE 2000 FT. REQUIRE THAT THE
FURNACE INPUT RATING BE ADJUSTED AND THAT
THE SIZE OF THE BURNER ORIFICES BE RECAL-
CULATED BASED ON ELEVATION AND GAS HEAT-
ING VALUE. THE BURNER ORIFICES MAY (OR MAY
NOT) NEED TO BE CHANGED.
SUPPLY GAS PRESSURE MEASUREMENT
1. With gas shut off to the furnace at the manual gas
valve outside the unit, remove the line pressure tap
plug on the gas valve. See Figure 40.
51
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