3. Verify natural gas input rate by clocking gas meter.
NOTE:
Be sure all pressure tubing, combustion-air and vent pipes, and burner enclosure front are in place when checking input by clocking gas
meter.
a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft, this furnace has been approved for a 2 percent derate for each 1000 ft above sea level. See Table 7 for derate
multiplier factor and example.
EXAMPLE:
100,000 Btuh input furnace installed at 4300 ft.
Furnace Input Rate at Sea Level
X
Derate Multiplier Factor
=
Furnace Input Rate at Installation Altitude
100,000
X
0.91
=
91,000
CANADA
At installation altitudes from 2000 to 4500 ft, this furnace must be derated 5 percent by an authorized Gas Conversion Station or Dealer.
To determine correct input rate for altitude, see example above and use 0.95 as derate multiplier factor.
b. Reinstall burner enclosure front.
NOTE:
Clocking gas input rate MUST always be performed with the burner enclosure front INSTALLED.
c. Check that gas valve adjustment caps are in place for proper input to be clocked.
d. Obtain average yearly heat value for local gas supply.
NOTE:
Be sure heating value of gas used for calculations is correct for your altitude. Consult local gas utility for altitude adjustment of gas heating
value.
e. Check and verify orifice size in furnace. NEVER ASSUME THE ORIFICE SIZE. ALWAYS CHECK AND VERIFY.
f. Turn off all other gas appliances and pilots.
g. Turn setup switch SW-2 to ON position. (See Fig. 16.) This keeps furnace locked in low-heat operation.
h. Let furnace run for 3 minutes in low-heat operation.
i. Measure time (in sec) for gas meter to complete 1 revolution. Note reading.
j. Refer to Table 5 for cubic ft of gas per hr.
Fig. 18—Burner Flame
A89020
BURNER FLAME
BURNER
MANIFOLD
Table 7—Altitude Derate Multiplier for U.S.A.
ALTITUDE (FT)
% OF DERATE
DERATE MULTIPLIER FACTOR FOR U.S.A.*
0—2000
0
1.00
2001—3000
4—6
0.95
3001—4000
6—8
0.93
4001—5000
8—10
0.91
5001—6000
10—12
0.89
6001—7000
12—14
0.87
7001—8000
14—16
0.85
8001—9000
16—18
0.83
9001—10,000
18—20
0.81
* Derate multiplier factor is based on midpoint altitude for altitude range.
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