Control Operating Sequence
Unit heaters are supplied with standing pilot control systems as
standard or intermittent pilot systems with continuous retry as an
option. On standing pilot and mechanical modulation systems the
main burner is turned off 100% when the thermostat is satisfied,
but the pilot remains lit. For intermittent pilot systems, except
mechanical modulation both the main burner and pilot burner are
turned off 100% when the thermostat is satisfied. Standing pilot
systems, for both natural and propane gas, have a manually lit
pilot which stays lit until the gas valve is manually turned to the off
position. On a call for heat, the gas valve opens, sending gas to
the burner allowing the unit to fire. Intermittent pilot systems, for
both natural and propane gas, the ignition controller is 100% shut-
off with continuous retry. On a call for heat, the system will attempt
to light the pilot for 70 seconds. If the pilot is not sensed for any
reason, the ignition control will wait for approximately six minutes
with the combination gas control closed and no spark. After six
minutes, the cycle will begin again. After three cycles, some
ignition controllers lockout for approximately one hour before the
cycle begins again. This will continue indefinitely until the pilot
flame is sensed or power is interrupted to the system. Refer to
table 14.1 for control code descriptions.
NOTE: Gas Control Options could change the listed sequence
of operation based on their function. The descriptions
given are for the basic unit heater.
Single-Stage Gas Controls (standing pilot)
Utilizes a single-stage combination gas control with a standing
pilot operator and a single-stage low voltage thermostat.
1. Pilot is lit continuously.
2. The thermostat calls for heat.
3. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes.
4. The main gas valve is opened and the main burner is lit to
100% full fire.
5. The air mover starts after 30 to 90 seconds.
6. The unit continues to operate until the thermostat is
satisfied, at which time the main valve closes 100%.
7. The air mover stops after 30 to 90 seconds.
Single-Stage Gas Controls (intermittent pilot)
Utilizes a single-stage combination gas, an ignition control, and
a single-stage low voltage thermostat.
1. The thermostat calls for heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot.
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. The air mover starts after 30 to 90 seconds.
7. The unit continues to operate until the thermostat is satisfied, at
which time both the main and pilot valves close 100%.
8. The air mover starts after 30 to 90 seconds.
13
Table 13.1
Manifold Pressure & Gas Consumption ➀
Natural Propane
BTU/Cu. Ft. 1050 2500 No. of
Model Specific Gravity 0.60 1.53 Orifices
Manifold Pressure In. W.C. 3.5 10.0
CFH 28.6 12.0
PDP 30 Gal/Hr. Propane – .33 1
Orifice Drill Size 38 52
CFH 47.6 20.0
Gal/Hr. Propane – .55 1
Orifice Drill Size 30 45
CFH 71.4 30.0
Gal/Hr. Propane – .82 1
Orifice Drill Size 21 39
CFH 95.2 40.0
Gal/Hr. Propane – 1.15 2
Orifice Drill Size 30 45
CFH 119.0 50.0
Gal/Hr. Propane – 1.43 2
Orifice Drill Size 26 43
CFH 138.1 58.0
Gal/Hr. Propane – 1.64 2
Orifice Drill Size 21 39
CFH 166.7 70.0
Gal/Hr. Propane – 1.86 3
Orifice Drill Size 28 43
CFH 190.5 80.0
Gal/Hr. Propane – 2.19 3
Orifice Drill Size 25 42
CFH 238.1 100.0
Gal/Hr. Propane – 2.74 3
Orifice Drill Size 18 36
CFH 285.7 120.0
Gal/Hr. Propane – 3.29 4
Orifice Drill Size 21 39
CFH 333.3 140.0
Gal/Hr. Propane – 3.84 5
Orifice Drill Size 23 41
CFH 381.0 160.0
PDP 400 Gal/Hr. Propane – 4.38 6
Orifice Drill Size 25 42
➀ Above gases based on average standards. Units can be
furnished for gases of different values and specific gravities.
(Gal./Hr. based on 60°F. 30" Hg., 91,500 BTU/Gal.) In Canada,
refer to rating plate on side of unit for orifices at high altitude.
START-UP PROCEDURE
Figure 13.1
Manifold Adjustment, Natural Gas
MANIFOLD
MIXER
TUBES
BURNER
RETAINING PIN
MAIN
BURNER
ORIFICES
MANIFOLD MOUNTING
SCREW AND PIN
Figure 13.2 - Air Shutter Adjustment, Propane Gas
MANIFOLD
MIXER
TUBES
MAIN
BURNER
ORIFICES
AIR
SHUTTER
PDP 50
BDP 50
PDP 75
BDP 75
PDP 100
BDP 100
PDP 125
BDP 125
PDP 150
BDP 150
PDP 175
BDP 175
PDP 200
BDP 200
PDP 250
BDP 250
PDP 300
BDP 300
PDP 350
BDP 350
