Tempstar F97CMN Installation, Start-Up, Operating And Service And Maintenance Instructions page 52

F97CMN and G97CMN: Installation, Start-up, Operating and Service and Maintenance Instructions
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The NATURAL GAS manifold pressure adjustments in Tables 18 and
19 compensate for BOTH altitude AND gas heating value. DO NOT
apply an additional derate factor to the pressures show in
Table 20. The values in this table are NOT referenced to sea level; they
are AS-MEASURED AT ALTITUDE.
The heating content of natural gas at altitude may already provide for a
reduction in capacity of the furnace. Be sure to obtain the expected
in-season gas heating value of the gas from the gas supplier BEFORE
making any adjustments for capacity or altitude. Refer to
Table 20. No adjustments to the furnace may be necessary at altitude
for certain gas heating values.
Refer to the instructions provided in the factory-specified LP/Propane
conversion kit for instructions for setting gas manifold pressures for
LP/Propane applications.
In the USA, the input rating for altitudes above 2000 ft. (609.6M) must
be reduced by 2 percent for each 1000 ft. (304.8M) above sea level.
Refer to Table 16.
In Canada, the input rating must be reduced by 5 percent for altitudes of
2000 ft. (609.6M) to 4500 ft. (1371.6M) above sea level. The natural gas
manifold pressures in Tables 18 and 19 adjust for BOTH altitude and
natural gas heating value.
Table 16 – Altitude Derate Multiplier for U.S.A.*
ALTITUDE
FT. M
0–2000 0-610
2001–3000 610-914
3001–4000 914-1219
4001–5000 1219-1524
5001–6000 1524-1829
6001–7000 1829-2134
7001–8000 2134-2438
8001–9000 2438-2743
9001–10,000 2743-3048
*Derate multiplier factors are based on midpoint altitude for altitude range.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (610 to 1372 M), use
USA altitudes of 2001 to 2000 ft. (611 to 914 M) in
To adjust manifold pressure to obtain the proper input rate, first,
determine if the furnace has the correct orifice installed. At higher
altitudes or different gas heat contents, it may be necessary to change the
factory orifice to a different orifice. Tables have been provided in the
furnace installation instructions to match the required orifice to the
manifold pressure to the heat content and specific gravity of the gas.
!
THERE ARE TWO MANIFOLD PRESSURE TABLES
Use Table 18 for all models EXCEPT (F/G)97CMN0602120
Use Table 19 for all models (F/G)97CMN0602120 ONLY
To do this:
1. Obtain average yearly gas heat value (at installed altitude) from
local gas supplier.
2. Obtain average yearly specific gravity from local gas supplier.
3. Find installation altitude range for your installation in the manifold
pressure tables. See Table 13
BTUh min-heat per burner or
Max-Heat/8,000 BTUh Min-Heat per burner.
4. Find closest natural gas heat value and specific gravity in
or Table 14 depending on furnace gas input rate.
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
NOTICE
Table 19
Table 19
PERCENT DERATE
OF MULTIPLIER
DERATE FACTOR*
0 1.00
4-6 0.95
6-8 0.93
8-10 0.91
10-12 0.89
12-14 0.87
14-16 0.85
16-18 0.83
18-20 0.81
Table 13.
NOTICE
for 20,000 BTUh Max-Heat/8,000
Table 14 for 20,200 BTUh
5. Follow heat value and specific gravity lines to point of intersection
to find orifice size and maximum and minimum manifold pressure
settings for proper operation.
6. Check and verify burner orifice size in furnace. NEVER ASSUME
ORIFICE SIZE. ALWAYS CHECK AND VERIFY.
or
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
or
essential for proper flame characteristics.
7. Replace original orifice with correct size, if required by
Table 14 depending on furnace gas input rate. Use only
factory-supplied orifices, see EXAMPLE 1.
EXAMPLE 1 - 80,000 BTUH INPUT:
EXAMPLE: 0 - 2000 ft. (0 - 609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
* Furnace is shipped with No. 44 orifices. In this example, all main
burner orifices are the correct size and do not need to be changed to
obtain proper input rate.
Manifold pressure: 3.4-in. w.c. for maximum heat, 0.55-in. w.c. for
minimum heat.
NOTE: To convert gas manifold Table pressures to Pascals, multiply the
in. w.c. value by 249.1 Pa/in. w.c. (1 in. w.c. = 249.1 Pa).
Check Inlet Gas Pressure
The inlet gas pressure must be checked with the furnace operating in
maximum heat. This is necessary to make sure the inlet gas pressure
does not fall below the minimum pressure of 4.5 in. w.c. for natural gas.
The maximum inlet gas pressure is 13.6 in. of water column. If the inlet
pressure is too low, you will not be able to adjust the manifold pressure
to obtain the proper input rate. To check the inlet gas pressure:
1. Make sure the gas supply is turned off to the furnace and at the
electric switch on the gas valve.
2. Loosen set screw on inlet tower pressure tap no more than one full
turn with a 3/32-in. hex wrench or remove the 1/8 in. NPT plug
from the inlet pressure tap on the gas valve.
3. Connect a manometer to the inlet pressure tap on gas valve.
4. Turn on furnace power supply.
5. Turn gas supply manual shutoff valve to ON position.
6. Turn furnace gas valve switch to ON position.
7. Jumper the R to W/W1 and W2 thermostat connections at the
furnace control board.
8. When main burners ignite, confirm inlet gas pressure is Between
4.5 in. w.c. and 13.6 in. w.c.
9. Remove jumper across thermostat connections to terminate call for
heat. Wait until the blower off delay is completed.
10. Turn furnace gas valve electric switch to OFF position.
11. Turn gas supply manual shutoff valve to OFF position.
12. Turn off furnace power supply.
13. Remove manometer from the inlet pressure tap of the gas valve.
Table 13
52
NOTICE
!
Table 13 or