22
Gas input rates on rating plate are for installations at altitudes up to
2000 ft. Input rate must be within
±
2% of rating plate input.
1. Determine the correct gas input rate.
a. The rated gas inputs shown in Table 4 are for altitudes
from sea level to 2000 ft above sea level. These inputs are
based on natural gas with a heating value of 1050 Btu/ft3
at .65 specific gravity.
IN THE U.S.A.:
The input rating for altitudes above 2,000 ft. must be reduced by 4
percent for each 1,000 ft. above sea level.
For installations below 2,000 ft., refer to the unit rating plate.
For installations above 2,000 ft., multiply the input by on the rating
plate by the derate multiplier in Table 6 for the correct input rate.
Table 6—
Altitude Derate Multiplier for U.S.A.
Altitude (Ft)
Percent of Derate
Derate Multiplier
Factor*
0--2000
0
1.00
2001--3000
8--12
0.90
3001--4000
12--16
0.86
4001--5000
16--20
0.82
5001--6000
20--24
0.78
6001--7000
24--28
0.74
7001--8000
28--32
0.70
8001--9000
32--36
0.66
9001--10,000
36--40
0.62
*Derate multiplier factors are based on midpoint altitude for altitude range.
IN CANADA:
The input rating for altitudes from 2,000 to 4,500 ft above sea level
must be derated 10 percent by an authorized Gas Conversion Station
or Dealer.
EXAMPLE:
90,000 Bhuh Input Furnace Installed at 4300 Ft.
Furnace Input Rate
Derate Multiplier
Furnace Input Rate
at Sea Level
X
Factor
=
at Installation Altitude
90,000
X
0.90
=
81,000
b. 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.
2. Adjust manifold pressure to obtain low stage input rate (See
Fig. 18).
a. Turn off gas supply to unit.
b. Remove pipe plug on manifold (See Fig. 19) and connect
manometer. Turn on gas supply to unit.
c. Turn gas valve switch to ON.
d. Set unit to run for 20 minutes in low--stage gas heat
operation using the ”INSTALLER CHECKOUT” menu
on the User Interface.
e. Remove regulator adjustment cap from low stage gas
valve pressure regulator (See Fig. 18) and turn low--stage
adjusting screw (3/16 or smaller flat--tipped screwdriver)
counterclockwise (out) to decrease rate and clockwise
(in) to increase input rate.
REGULATOR COVER SCREW
PLASTIC ADJUST SCREW
LOW STAGE
GAS PRESSURE
REGULATOR ADJUSTMENT
MANIFOLD
PRESSURE TAP
INLET
PRESSURE TAP
ON/OFF SWITCH
REGULATOR SPRING
HIGH STAGE GAS
PRESSURE REGULATOR
ADJUSTMENT
A04167
Fig. 18 -- Redundant Automatic Gas Control Valve
NOTE
: DO NOT set low stage manifold pressure less than 1.4 in
wc or more than 2.0 in wc for natural gas. If manifold pressure is
outside this range, change main burner orifices.
f. Re--install low stage regulator adjustment cap.
g. Leave manometer connected.
NOTE
: If orifice hole appears damaged or it is suspected to have
been re--drilled, check orifice hole with a numbered drill bit of the
correct size. Never re--drill an orifice. A burr--free and squarely
aligned orifice hole is essential for proper flame characteristics.
3. Verify natural gas low stage input rate.
a. Turn off all other gas appliances and pilots served by the
gas meter.
b. If unit is not running, set unit to run for 20 minutes in
low--stage gas heat operation using the ”INSTALLER
CHECKOUT” menu on the UI.
c. Record number of seconds for gas meter to complete one
revolution.
d. Divide number of seconds in step c. into 3600 (number
of seconds in 1 hour).
e. Multiply result of step d. by the number of cubic feet
shown for one revolution of test dial to obtain cubic feet
of gas flow per hour.
f. Multiply result of step f. by Btu heating value of the gas
to obtain total measured input shown in Table 4. (Consult
the local gas supplier if the heating value of gas is not
known).
EXAMPLE: Assume a 90,000 high stage input unit is being
installed. Assume that the size of the dial is 2 cubic ft., one
revolution takes 129 sec., and the heating value of the gas is 1050
Btu/ft3. Proceed as follows:
a. 129 sec. to complete one revolution
b. 3600/129 = 27.9
c. 27.9 x 2 = 55.8 ft3 of gas flow/hr.
d. 55.8 x 1050 = 58,590 Btuh input.
In this example, the nominal input rate for low stage is 58,500
Btu/hr, so the low stage manifold pressure is correctly set.
If the measured low stage rate is too low, increase the manifold
pressure to increase rate. If the measured low stage rate is too high,
decrease the manifold pressure to decrease rate.
NOTE
: Double--check that UI is running on low stage gas heat
while clocking the low stage firing rate.
4. Verify proper low stage gas heat temperature rise.
48D
U
