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At altitudes above 2000 ft, this furnace has been ap-
proved for a 2 percent derate for each 1000 ft above sea
level. See Table 13 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 box cover.
NOTE: Clocking gas input rate MUST always be performed with
the burner box cover INSTALLED.
c. Check that gas valve adjustment caps are in place for
proper input to be clocked.
d. Obtain yearly heat value average 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 AS-
SUME 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. 25.)
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 14 for cubic ft of gas per hr.
k. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).
l. Turn setup switch SW-2 to OFF position and jumper R
and W2 thermostat connections. (See Fig. 25.) This keeps
furnace locked in high-heat operation. Repeat items h
through k for high-heat operation.
EXAMPLE: (High-heat operation at 0—2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 975 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 14)
Btu heating input = 103 X 975 = 100,425 Btuh In this
example, the orifice size and manifold pressure adjustment
is within ±2 percent of the furnace input rate.
NOTE: Measured gas inputs (high heat and low heat) must be
within ±2 percent of that stated on furnace rating plate when
installed at sea level or derated per that stated above when installed
at higher altitudes.
m. Remove jumper across R, W/W1, and W2 thermostat
connections to terminate call for heat.
CAUTION: DO NOT redrill orifices. Improper drilling
(burrs, out-of-round holes, etc.) can cause excessive
burner noise and misdirection of burner flames. This can
result in flame impingement of burners and heat exchang-
ers, causing failures.
A93059
BURNER
ORIFICE
Fig. 49—Burner Flame
A89020
BURNER FLAME
BURNER
MANIFOLD
TABLE 13—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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