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LAARS HEATING SYSTEMS
By setting the gas offset pressure and gas orifice
differential pressure according to Table 11, the correct
input rate and gas to air ratio is achieved.
GAS
GAS ORIFICE
UNFIRED
ELEVATION,
OFFSET
DIFFERENTIAL
VENTURI
FT
PRESSURE
PRESSURE
DIFFERENTIAL
inch W.C.
inch W.C.
inch W.C.
SEA LEVEL
+0.4
+4.0
+5.8
2000
+0.4
+3.7
+5.3
4000
+0.4
+3.4
+4.9
6000
+0.4
+3.2
+4.6
8000
+0.4
+2.9
+4.2
10000
+0.4
+2.7
+3.9
Table 11. Venturi Pressure Settings.
3F-3. Venturi Setup Procedure
1.
Loosen the nut on the blower shutter to allow for
adjustment. Turn the heater on so that the blower
is running and the heater is not firing. Measure
the unfired venturi differential pressure. In this
unfired condition, adjust the shutter until the
unfired venturi differential pressure is according
to Table 1, “Unfired Venturi Differential” (5.8 ±
.3 inches wc at sea level). If this pressure range
can not be achieved, check for blockage in the
combustion air inlet, boiler and venting system.
If there is no obvious cause contact a qualified
Laars service technician.
2.
Approximately 40 seconds after the blower starts
the gas valves will open. The heater is now
firing. If the heater is not running, check all
manual gas valves and heater safety devices.
Ensure proper gas supply pressures according to
Table 4 in Section 2.
3.
Measure the gas offset pressure. Using the
regulator only, adjust the gas offset pressure
according to the installation’s altitude in Table
11 (+0.4 inches wc. at sea level). REPLACE
THE REGULATOR CAP BEFORE TAKING
GAS PRESSURE READINGS. Turn the
regulator screw clockwise to decrease the gas
offset pressure, turn the regulator screw
counterclockwise to increase the offset.
4.
Using the toggle switch, turn the heater off. Turn
the heater back on and check the gas offset
pressure while the heater is firing. If the gas
offset pressure is not according to Table 11,
adjust the regulator as needed.
5.
Measure the gas orifice differential pressure.
This pressure must be adjusted according to
Table 1 (4.0 ± .2 inches wc at sea level). Use the
blower shutter to adjust the gas orifice
differential.
6.
By adjusting the gas orifice differential, the gas
offset pressure will change. Therefore you must
repeat steps 3-5 until the gas offset and gas
orifice differential pressures are according to
Table 11.
7.
After setting all pressures, turn the heater off and
replace each shutoff valve with the factory
installed threaded plugs. The venturi has now
been adjusted for proper operation.
SECTION 4.
Maintenance
4A. General Instructions
1.
Oil the water circulating pump in accordance
with the manufacturer's instructions.
2.
Oil the blower motor bearings every 6 months.
3.
If a strainer is used in a pressure reducing valve
or in the piping, clean it every 6 months in
accordance with the manufacturer's instructions.
4.
At startup and every 6 months after, look at the
main burner flame for proper performance. The
burner should not require maintenance in normal
operation. If any malfunction indicates that the
burner needs service (e.g., a flame that is yellow,
or entire burner surface glowing red), call a
professional service technician. Flame
characteristics may be inspected during the first
30 seconds after ignition. Characteristics of a
good flame are:
a.
Blue flame color.
b.
Dark-colored burner surface with
occasional glowing fibers on surface.
NOTE: After 30 seconds of operation the
combustion chamber will heat up and prevent reliable
flame observation.
5.
Inspect the venting system for blockage, leakage,
and corrosion at least once a year.
6.
Keep the heater area clear of combustible
material, gasoline, and other flammable liquids
and vapors.
7.
Be sure all combustion air and ventilation
openings are not blocked.
8.
After installation and first startup, check the heat
exchanger for black carbon soot buildup after the
following periods of operation: 24 hours, 7 days,
30 days, 90 days, and once every 6 months
thereafter.
4B. Heat Exchanger
Black carbon soot buildup on the external
surfaces of the heat exchanger is caused by one or
more of the following: incomplete combustion,
combustion air problems, venting problems and heater
short cycling. As soon as any buildup is seen, correct
the cause of the buildup. Scale can build up on the
