17
Table 6 - Main Burner Orifi ce Schedule*
PILOT ADJUSTMENT
1. Remove the PILOT ADJUSTMENT CAP.
2. Adjust the pilot screw to provide a properly sized
fl ame.
3. A proper fl ame is a soft, steady fl ame that envelops
3
/
8
to
1
/
2
inch (9.5 to 12.7mm) of the fl ame sensor.
4. Replace the pilot adjustment cap.
MANIFOLD PRESSURE ADJUSTMENT
If the manifold pressure requires adjustment, remove
the cap from the pressure regulator and turn the
adjustment screw clockwise to increase the pressure,
and counterclockwise to decrease the pressure. The
adjusted manifold pressure should not vary more
than 10% from the pressures specifi ed in Table 6.
* This schedule is for units operating at normal altitudes of 2000 ft. (610m) or
less. Special orifi ces are required for installations above 2000 feet (610m).
When installed in Canada, any references to deration at altitudes in excess of
2000 feet (610m) are to be ignored. At altitudes of 2000 to 4500 feet (610 to
1372m), the unit heaters must be orifi ced to 90% of the normal altitude rating,
and be so marked in accordance with the CSA certifi cation.
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
*
INPUT
IN
1000
BTU
NO. OF
BURNER
ORIFICES
3.5" W.C.
(0.9 kPa)
1
0.5" W.C.
(2.6 kPa)
MANIFOLD
PRESSURE
PROPANE
TYPE OF GAS
NATURAL
2500 BTU/Ft
3
(93.1 MJ/m
3
)
1075 BTU/Ft
3
(40.1 MJ/m
3
)
HEATING
VALUE
100
125
150
175
200
225
250
300
350
400
4
5
6
7
8
9
10
12
14
16
96
42
120
42
140
42
163
42
186
42
210
42
233
42
280
42
326
42
372
42
40
54
50
54
60
54
70
54
80
54
90
54
100
54
120
54
140
54
160
54
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
FT
3
/HR
ORIFICE DRILL
GAS INPUT RATE
Never overfi re the duct furnace, as this
may cause unsatisfactory operation, or shorten the
life of the heater.
Check the gas input rate as follows (Refer to General
Safety Information section for metric conversions).
1. Turn off all gas appliances that use gas through the
same meter as the unit heater.
2. Turn the gas on to the unit heater.
3. Clock the time in seconds required to burn 1 cubic
foot of gas by checking the gas meter.
4. Insert the time required to burn one cubic foot of gas
into the following formula and compute the input rate
3600 (Sec. per Hr.) x BTU/Cu./Ft.
= Input Rate
Time (Sec.)
For example, assume the BTU content of one cubic foot
of gas is 1000, and that it takes 18 seconds to burn one
cubic foot of gas.
3600 x 1000
= 200,000
18
NOTICE: If the computation exceeds, or is less than
95% of the gas BTU/hr. input rating (see Table 2),
adjust the gas pressure.
Adjust the gas pressure as follows:
1. NATURAL GAS: Best results are obtained when the
duct furnace is operating at its full rated input with
the manifold pressure of 3.5 inches W.C. (0.9 kPa).
Adjustment of the pressure regulator is not normally
necessary since it is preset at the factory. However,
fi eld adjustment may be made as follows:
a. Attach manometer at the pressure tap
plug below the control outlet.
b. Remove the regulator adjustment screw cap,
located on the combination gas valve.
c. With a small screwdriver, rotate the adjustment
screw clockwise to increase pressure.
d. Replace regulator adjustment screw cap.
2. PROPANE GAS: An exact manifold pressure of 10.0
inches W.C. (2.5 kPa) must be maintained for proper
operation of the duct furnace. If the unit is equipped
with a pressure regulator on the combination gas
valve, follow steps “a” through “d” above. If the unit is
not so equipped, the propane gas supply system
pressure must be regulated to attain this manifold
operating pressure.
