a. Calculate high-altitude adjustment (if required).
UNITED STATES
At altitudes above 2000 ft, this furnace has been ap-
proved for a 4 percent derate for each 1000 ft above sea
level. See Table 8 for derate multiplier factor and
example.
EXAMPLE:
85,000 Btuh input furnace installed at 4300 ft.
Furnace Input
Rate at
Sea Level
X
Derate
Multiplier
Factor
=
Furnace Input Rate
at Installation
Altitude
85,000
X
0.82
=
69,700
CANADA
At installation altitudes from 2000 to 4500 ft, this
furnace must be derated 10 percent by an authorized Gas
Conversion Station or Dealer. To determine correct input
rate for altitude, see example above and use 0.82 as
derate multiplier factor.
b. Check that gas valve adjustment caps are in place for
proper input to be clocked.
c. 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.
d. Check and verify orifice size in furnace. NEVER AS-
SUME THE ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.
e. Turn off all other gas appliances and pilots.
f. Move setup switch SW-2 to ON position. (See Fig. 12.)
This keeps furnace locked in low-heat operation.
g. Jumper R to W/W1.
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 10 for cubic ft of gas per hr.
k. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).
l. Move setup switch SW-2 to OFF position and jumper R
and W2 thermostat connections. (See Fig. 12.) 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 85,000 Btuh
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 1050 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 92 sec
Gas rate = 80 cu ft/hr (from Table 10)
Btu heating input = 80 X 1050 = 84,000 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.
5. Set temperature rise.
Place SW-2 in ON position. Jumper R to W/W1 and W2 to
check high-gas-heat temperature rise. To check low-gas-
heat temperature rise, remove jumper to W2. Determine air
temperature rise for both high and low fire. Do not exceed
temperature rise ranges specified on unit rating plate for
high and low fire.
a. Place duct thermometers in return and supply ducts as
near furnace as possible. Be sure thermometers do not
see heat exchangers so that radiant heat will not affect
thermometer readings. This is particularly important
with straight run ducts.
b. When thermometer readings stabilize, subtract return-air
temperature from supply-air temperature to determine
temperature rise.
NOTE:
If the temperature rise is outside this range, first check:
(1.) Gas input for low- and high-fire operation.
(2.) Derate for altitude if applicable.
(3.) Return and supply ducts for excessive restrictions
causing static pressures greater than 0.50-in. wc.
c. Adjust air temperature rise by adjusting blower speed.
Increase blower speed to reduce temperature rise. De-
crease blower speed to increase temperature rise. For
high fire, speed selection can be med-high, med (5-speed
blowers only), or med-low (factory setting). For low fire,
speed selection can be low (factory setting), med-low, or
med (5-speed blowers only).
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
TABLE 8—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
8—12
0.90
3001—4000
12—16
0.86
4001—5000
16—20
0.82
5001—6000
20—24
0.78
6001—7000
24—28
0.74
7001—8000
18—32
0.70
8001—9000
32—36
0.66
9001—10,000
36—40
0.62
* Derate multiplier factor is based on midpoint altitude for altitude range.
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