Carrier 58MXA - Page 36

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% derate for each 1000 ft above sea level. See Table
8 for derate multiplier factor.
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% by an authorized Gas Conversion
Station. To determine correct input rate for altitude, see
example above and use 0.95 as derate multiplier factor.
b. Turn off all other gas appliances and pilots.
c. Start furnace and let operate for 3 minutes.
d. Measure time (in sec) for gas meter test dial to complete 1
revolution.
e. Refer to Table 9 for cu ft of gas per hr.
f. Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft) using
natural gas heating value from local gas utility/supplier.
EXAMPLE: (0—2000 ft altitude)
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 9)
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.
Table 7—Model 58MXA Orifice Size and Manifold Pressure for Correct Input Continued
(Tabulated Data Based on 20,000 Btuh per Burner, Derated 2% for Each 1000 Ft Above Sea Level)
ALTITUDE
RANGE
(FT)
AVG GAS
HEAT VALUE
AT ALTITUDE
(BTU/CU FT)
SPECIFIC GRAVITY OF NATURAL GAS
0.58 0.60 0.62 0.64 0.66
Orifice
No.
Manifold
Pressure
Orifice
No.
Manifold
Pressure
Orifice
No.
Manifold
Pressure
Orifice
No.
Manifold
Pressure
Orifice
No.
Manifold
Pressure
U.S.A. Only
575 43 3.8 42 3.2 42 3.3 42 3.5 42 3.6
600 43 3.5 43 3.6 43 3.7 42 3.2 42 3.3
9001 625 44 3.7 44 3.8 43 3.5 43 3.6 43 3.7
650 44 3.4 44 3.5 44 3.7 44 3.8 43 3.4
to 675 45 3.8 44 3.3 44 3.4 44 3.5 44 3.6
700 45 3.6 45 3.7 45 3.8 44 3.3 44 3.4
10,000 725 45 3.3 45 3.4 45 3.6 45 3.7 45 3.8
750 45 3.1 45 3.2 45 3.3 45 3.4 45 3.5
775 45 2.9 45 3.0 45 3.1 45 3.2 45 3.3
Fig. 46—Burner Flame
A89020


BURNER FLAME
BURNER
MANIFOLD
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 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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