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Check Gas Input
Check gas input and manifold pressure after unit start- -up (See
Table 6). If adjustment is required proceed as follows:
S The rated gas inputs shown in Table 6 are for altitudes from sea
level to 2000 ft (610 m) above sea level. These inputs are based
on natural gas with a heating value of 1025 Btu/ft
specific gravity, or propane gas with a heating value of 2500
3
Btu/ft
at 1.5 specific gravity.
IN THE U.S.A.:
The input rating for altitudes above 2,000 ft (610 m) must be
reduced by 4% for each 1,000 ft (305 m) above see level.
For installations below 2,000 ft (610 m), refer to the unit rating
plate.
For installations above 2,000 ft (610 m). multiply the input on the
rating plate by the derate multiplier in Table 3 for correct input rate.
Table 3 – Altitude Derate Multiplier for U.S.A.*
ALTITUDE FT (M)
PERCENT OF DERATE
0--- 2000
0
(0--- 610)
2001--- 3000*
8--- 12
(610--- 914)
3001--- 4000
12--- 16
(915--- 1219)
4001--- 5000
16--- 20
(1220--- 1524)
5001--- 6000
20--- 24
(1524 --- 1829)
6001--- 7000
24--- 28
(1829--- 2134)
7001--- 8000
28--- 32
(2134--- 2438)
8001--- 9000
32--- 36
(2439--- 2743)
9001--- 10,000
36--- 40
(2744--- 3048)
*In Canada see Canadian Altitude Adjustment.
{Derate multiplier factors are based on midpoint altitude for altitude range.
IN CANADA:
The input rating for altitudes from 2,000 (610 m) to 4,500 ft (1372
m) above sea level must be derated 10% by an authorized Gas
Conversion Station or Dealer.
EXAMPLE:
90,000 Btu/hr Input Furnace Installed at 4300 ft.
Furnace Input Rate at
X Derate Multiplier
Sea Level
Factor
90,000
X
When the gas supply being used has a different heating value or
specific gravity, refer to national and local codes, or contact your
distributor to determine the required orifice size.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in reduced unit
and/or component life.
Do Not redrill an orifice. Improper drilling (burrs,
out- -of- -round holes, etc.) can cause excessive burner noise
and misdirection of burner flame. If orifice hole appears
damaged or it is suspected to have been redrilled, check
orifice hole with a numbered drill bit of correct size.
Adjust Gas Input
The gas input to the unit is determined by measuring the gas flow
at the meter or by measuring the manifold pressure. Measuring the
3
at 0.60
DERATE MULTIPLIER
FACTOR{
1.00
0.90
0.86
0.82
0.78
0.74
0.70
0.66
0.62
= Furnace Input Rate at
Installation Altitude
0.90
=
81,000
gas flow at the meter is recommended for natural gas units. The
manifold pressure must be measured to determine the input of
propane gas units.
Measure Gas Flow (Natural Gas Units)
Minor adjustment to the gas flow can be made by changing the
manifold pressure. The manifold pressure must be maintained
between 3.2 and 3.8 IN. W.C.
ON/OFF SWITCH
INLET
PRESSURE TAP
Fig. 13 - - Single- -Stage Gas Valve
If larger adjustments are required, change main burner orifices
following the recommendations of national and local codes.
NOTE:
All other appliances that use the same meter must be
turned off when gas flow is measured at the meter.
Proceed as follows:
1. Turn off gas supply to unit.
2. Remove pipe plug on manifold (See Fig. 11) and connect
manometer. Turn on gas supply to unit.
3. Record number of seconds for gas meter test dial to make
one revolution.
4. Divide number of seconds in Step 3 into 3600 (number of
seconds in one hr).
5. Multiply result of Step 4 by the number of cubic feet (cu ft)
shown for one revolution of test dial to obtain cubic feet (cu
ft) of gas flow per hour.
6. Multiply result of Step 5 by Btu heating value of gas to
obtain total measured input in Btuh. Compare this value
with heating input shown in Table 6 (Consult the local gas
supplier if the heating value of gas is not known).
EXAMPLE: Assume that the size of test dial is 1 cu ft, one
revolution takes 32 sec, and the heating value of the gas is 1050
3
Btu/ft
. Proceed as follows:
1. 32 sec. to complete one revolution.
2. 3600 32 = 112.5.
3
3. 112.5 x 1 =112.5 ft
of gas flow/hr.
4. 112.5 x 1050 = 118,125 Btuh input.
If the desired gas input is 115,000 Btuh, only a minor change in the
manifold pressure is required.
Observe manifold pressure and proceed as follows to adjust gas
input:
1. Remove regulator cover screw over plastic adjustment
screw on gas valve (See Fig. 13).
2. Turn plastic adjustment screw clockwise to increase gas
input, or turn plastic adjustment screw counterclockwise to
decrease input (See Fig. 13). Manifold pressure must be
between 3.2 and 3.8 IN. WC.
14
REGULATOR
COVER SCREW
PLASTIC
ADJUSTMENT
SCREW
REGULATOR SPRING
(PROPANE - WHITE)
(
NATURAL - SILVER)
GAS PRESSURE
REGULATOR
ADJUSTMENT
MANIFOLD
PRESSURE TAP
A07751
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