(4.) Burner flame should be clear blue, almost transpar-
ent. (See Fig. 18.)
c. Verify natural gas input rate by clocking gas meter.
NOTE:
High -Altitude Adjustment
UNITED STATES
At installation altitudes above 2000 ft, this furnace has been
approved for a 4 percent derate for each 1000 ft above sea level.
See Table 8 for derate multiplier factor.
CANADA
At installation altitudes from 2000 to 4500 ft, this furnace must be
derated 10 percent by an authorized Gas Conversion Station. To
determine correct input rate for altitude, see example above and
use 0.90 as derate multiplier factor.
a. Turn off all other gas appliances and pilots.
b. Start furnace and let operate for 3 minutes.
c. Measure time (in sec) for gas meter test dial to complete
1 revolution.
d. Refer to Table 9 for cu ft of gas per hr.
e. Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft)
using natural gas heating value from local gas
utility/supplier.
TABLE 7—MODEL 376CAV ORIFICE SIZE† AND MANIFOLD PRESSURE FOR CORRECT INPUT (CONTINUED)
(TABULATED DATA BASED ON 23,000 BTUH PER BURNER, DERATED 4 PERCENT FOR EACH 1000 FT ABOVE SEA
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
9001
to
10,000
575
43
3.0
43
3.1
43
3.2
43
3.3
43
3.4
600
43
2.7
43
2.8
43
2.9
43
3.0
43
3.1
625
43
2.5
43
2.6
43
2.7
43
2.8
43
2.8
650
43
2.3
43
2.4
43
2.5
43
2.6
43
2.6
675
43
2.1
43
2.2
43
2.3
43
2.4
43
2.4
700
48
3.8
43
2.1
43
2.1
43
2.2
43
2.3
725
48
3.5
48
3.6
48
3.7
43
2.1
43
2.1
750
49
3.8
48
3.4
48
3.5
48
3.6
48
3.7
775
49
3.6
49
3.7
49
3.8
48
3.4
48
3.5
* For size 060135 only, input is 22,500 Btuh per burner. Deduct 0.1-in. wc from manifold pressure shown in table. Change orifice size if manifold pressure falls below 3.2-in.
wc on altitudes up to 2000 ft, otherwise change orifice size if manifold pressure falls below 2.0-in. wc.
†Orifice sizes shown in SHADING are factory installed.
Fig. 17—Redundant Automatic Gas Control Valve
A00238
Fig. 18—Burner Flame
A89020
;;
;;
BURNER FLAME
BURNER
MANIFOLD
TABLE 8—ALTITUDE DERATE MULTIPLIER FOR U.S.A.
ALTITUDE
(FT)
PERCENT 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
28—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.
EXAMPLE:
92,000 BTUH INPUT FURNACE INSTALLED AT 4300 FT.
Furnace Input
Rate at
Sea Level
Derate
Multiplier
Factor
Furnace Input Rate
at Installation
Altitude
X
=
92,000
0.82
75,440
—18—
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