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Table 8—Model 58RAV Orifice Size† and Manifold Pressure for Correct Input
(Tabulated Data Based on 23,000 BTUH Per Burner, Derated 4 Percent per 1000 Ft Above Sea Level)*
AVG GAS
ALTITUDE
HEAT VALUE
RANGE
AT ALTITUDE
(FT)
(BTU/CU FT)
575
600
9001
625
650
to
675
700
10,000
725
750
775
* For size 135-20 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 BOLD are factory installed.
NOTE: This furnace has been approved for a manifold pressure
of 3.2-in. wc to 3.8-in. wc when installed at altitudes up to 2000 ft.
For altitudes above 2000 ft, the manifold pressure can be adjusted
from 2.0-in. wc to 3.8-in. wc.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result in
excess overfire and heat exchanger failures.
NOTE: If orifice hole appears damaged or it is suspected to have
been redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr-free and squarely
aligned orifice hole is essential for proper flame characteristics.
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 exchangers, causing fail-
ures..
(3.) After correct manifold pressure is obtained, replace
gas valve regulator adjustment screw cap and verify
adjusted gas input rate using method outlined in item
c.
0.58
0.60
Orifice
Manifold
Orifice
No.
Pressure
No.
43
3.0
43
43
2.7
43
43
2.5
43
43
2.3
43
43
2.1
43
48
3.8
43
48
3.5
48
49
3.8
48
49
3.6
49
BURNER
ORIFICE
A93059
SPECIFIC GRAVITY OF NATURAL GAS
0.62
Manifold
Orifice
Manifold
Pressure
No.
Pressure
3.1
43
3.2
2.8
43
2.9
2.6
43
2.7
2.4
43
2.5
2.2
43
2.3
2.1
43
2.1
3.6
48
3.7
3.4
48
3.5
3.7
49
3.8
(4.) Burner flame should be clear blue, almost transparent.
(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 7 for derate multiplier factor.
EXAMPLE:
92,000 Btuh input furnace installed at 4300 ft.
Furnace Input
Rate at
Sea Level
92,000
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.
EXAMPLE: (0—2000 ft altitude)
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 = 82 sec
Gas rate = 88 cu ft/hr (from Table 9)
Btu heating input = 88 X 1050 = 92,400 Btuh
In this example, the orifice size and manifold pressure
adjustment is within ±2 percent of the furnace input rate.
2. Set temperature rise.
Furnace must operate within range of temperature rise speci-
fied on the unit rating plate. Determine the air temperature rise
as follows.
18
(Continued)
0.64
Orifice
Manifold
Orifice
No.
Pressure
No.
43
3.3
43
43
3.0
43
43
2.8
43
43
2.6
43
43
2.4
43
43
2.2
43
43
2.1
43
48
3.6
48
48
3.4
48
Derate
Furnace Input Rate
X
Multiplier
=
at Installation
Factor
Altitude
X
0.82
=
75,440
0.66
Manifold
Pressure
3.4
3.1
2.8
2.6
2.4
2.3
2.1
3.7
3.5
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