440 01 4801 00
59
Specifications subject to change without notice.
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
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.
!
WARNING
BURNER
ORIFICE
A93059
Fig. 63 -- Orifice Hole
For proper operation and long term reliability, the Furnace input
rate must be /--2 percent of input rate on furnace rating
plate, or as adjusted for altitude.
The gas input rate on rating plate is for installations at altitudes up
to 2000 ft. (609.6M).
The NATURAL GAS manifold pressure adjustments in Table
20 compensate for BOTH altitude AND gas heating value.
DO NOT apply an additional derate factor to the pressures
shown 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.
NOTICE
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 18. The natural gas manifold pressures in
Table 20 adjust for BOTH altitude and natural gas heating value.
Table 18 – Altitude Derate Multiplier for USA
ALTITUDE
PERCENT
OF
DERATE
DERATE
MULTIPLIER
FACTOR*
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
*Derate multiplier factors are based on midpoint altitude for altitude range.
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 Table 20 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 Table 20.
4. Find closest natural gas heat value and specific gravity in
Table 20. 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.
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.
NOTICE
6. Replace orifice with correct size, if required by
Table
20.
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.
