F96VTN and G96VTN: Installation, Start-up, Operating and Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
54
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
. The natural gas manifold pressures in
for BOTH altitude and natural gas heating value.
Table 18 – Altitude Derate Multiplier for USA
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
adjust for BOTH altitude and natural gas
heating value.
NOTE:
For Canadian altitudes of 2000 to 4500 ft. (609.6 to 1371.6M),
use USA altitudes of 2001 to 3000 ft. (609.6 to 914.4M).
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. To
do this:
1. Obtain average yearly gas heat value (at installed altitude) from
local gas supplier.
2. Obtain average yearly gas specific gravity from local gas supplier.
3. Find installation altitude in
.
4. Find closest natural gas heat value and specific gravity in
.
Follow heat value and specific gravity lines to point of intersection
to find orifice size and low-and high-heat manifold pressure
settings for proper operation.
5. Check and verify burner orifice size in furnace. NEVER ASSUME
ORIFICE SIZE. ALWAYS CHECK AND VERIFY.
6. Replace orifice with correct size, if required by
. Use only
factory-supplied orifices. See EXAMPLE 1.
EXAMPLE 1
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 high heat, 1.4-in. w.c. for low 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 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.
14. Tighten set screw on inlet pressure tap with 3 /32-in. hex wrench, or
if 1/8-in. NPT plug was removed, apply pipe dope sparingly to end
of plug and re-install in the gas valve.
NOTICE
!
The NATURAL GAS manifold pressure adjustments in
compensate for BOTH altitude AND gas heating value. DO NOT apply
an additional derate factor to the pressures shown in
. 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
. 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.
ALTITUDE
PERCENT
OF
DERATE
DERATE
MULTIPLIER
FACTOR
*
*. Derate multiplier factors are based on midpoint altitude for altitude range.
FT.
M
0–2000
0-610
0
1.00
2001–3000
610-914
4-6
0.95
3001–4000
914-1219
6-8
0.93
4001–5000
1219-1524
8-10
0.91
5001–6000
1524-1829
10-12
0.89
6001–7000
1829-2134
12-14
0.87
7001–8000
2134-2438
14-16
0.85
8001–9000
2438-2743
16-18
0.83
9001–10,000
2743-3048
18-20
0.81
NOTICE
!
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.
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal injury, death,
and/or property damage.
Inlet pressure tap set screw must be tightened and 1/8-in. NPT pipe
plug must be installed to prevent gas leaks.
