Start-Up
28
GMND-SVX01B-EN
Gas Input Rate
Check the gas input rate as follows:
1.
Turn off all gas appliances that utilize gas through the
same gas meter as the unit heater.
2. Turn gas on to the unit heater.
3. Using the gas meter, clock the time that it takes to burn
one cubic foot of gas (Heating Value).
4. Insert the time, in seconds, into the formula below:
Example: If the heating value = 1000 BTU/ft
3
and the time/
ft
3
= 18 s/ft
3
then
Input Rate = 200,000 BTU/hr
(Refer to
“General Safety Information,” p. 7
for metric
conversions.)
Note:
If the computation exceeds, or is less than 95
percent of the gas Btu/h input rating (see
“Unit
Dimensions and Weights,” p. 10
), adjust the gas
pressure:.
Gas Pressure Adjustments
Adjust the gas pressure as follows:
1.
NATURAL GAS: Best results are obtained when the
duct furnace is operating at its full input rating with the
manifold pressure of 3.5 inches wc (0.9 kPa).
Adjustment of the pressure regulator is not normally
necessary since it is preset at the factory.
However, field adjustment may be made as follows:
a. Attach manometer at 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 wc (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
Step a
through
Step d
(above). If the unit
is not so equipped, the propane gas supply system
pressure must be regulated to attain this manifold
operating pressure.
Primary Air Shutter Adjustment
After the unit has been operating for at least 15 minutes,
adjust the primary air flow to the burners. Turn the friction-
locked, manually-rotated air shutters clockwise to close, or
counterclockwise to open.
For correct air adjustment, close the air shutter until yellow
tips in the flame appear. Then open the air shutter to the
point just beyond the position where yellow tipping
disappears. Refer to
Figure 19
.
Note:
There may be momentary and spasmodic orange
flashes in the flame. This is caused by the burning
of airborne dust particles, and should not be
confused with the yellow tipping, which is a stable
or permanent situation when there is insufficient
primary air.
NOTICE:
Overfiring!
Never overfire the duct furnace, as this could cause
unsatisfactory operation, or shorten the life of the
heater.
Input Rate =
Heating Value (Btu/ft
3
) (3600 s/hr)
Time (s/ft
3
)
Input Rate =
(1000 BTU/ft
3
) (3600 s/hr)
18 s/ft
3
Table 7.
Main burner orifice schedule
(a)
(a) This schedule is for units operating at normal altitudes of 2000 feet
(610 m) or less. SPECIAL ORIFICES ARE REQUIRED FOR INSTALLA-
TIONS ABOVE 2,000 FEET (610 m).
Input in
1000
BTU
(a)
Type of Gas Natural
Propane
No. of
Burner
Orifices
Heating
Value
1075 BTU/ft
3
(40.1 MJ/m
3
)
2500 BTU/ft
3
(93.1 MJ/m
3
)
Manifold
Pressure
3.5” wc (0.9 kPA) 10.5” wc (2.6 kPA)
100
ft
3
/hr
96
40
4
Orifice Drill
42
54
125
ft
3
/hr
120
50
5
Orifice Drill
42
54
150
ft
3
/hr
140
60
6
Orifice Drill
42
54
175
ft
3
/hr
163
70
7
Orifice Drill
42
54
200
ft
3
/hr
186
80
8
Orifice Drill
42
54
225
ft
3
/hr
210
90
9
Orifice Drill
42
54
250
ft
3
/hr
233
100
10
Orifice Drill
42
54
300
ft
3
/hr
280
120
12
Orifice Drill
42
54
350
ft
3
/hr
326
140
14
Orifice Drill
42
54
400
ft
3
/hr
372
160
16
Orifice Drill
42
54
Note:
When installed in Canada, any references to deration at altitudes in
excess of 2000 feet (610 m) are to be ignored. At altitudes of 2000
to 4500 feet (610 to 1372 m), the unit heaters must be orificed to
90 percent of the normal altitude rating, and be so marked in
accordance with the CSA certification.
