PLB-112
Oil Furnaces
–
Furnace Manual
12
11/13
2.3.3.
Combustion Check
The heat exchanger metal surfaces may have oil
and the baffle insulation also contains binders.
These products will burn or evaporate when the
unit operates for the first time. Because of that, the
smoke reading may be skewed during the first
minutes of operation. Therefore, the unit must
operate during at least 60 minutes before taking
any readings to adjust the combustion quality. Let
the unit cool down before making any adjustments.
The combustion check verification MUST be
performed after the nozzle replacement or the
burner cleaning. After these manipulations, the
combustion parameters are necessarily modified.
Refer also to the burner instruction manual.
1.
Pierce a test hole in the flue pipe, approximately 18 inches from
the furnace breech. Insert the smoke test probe into the hole.
For installation using a sidewall venting, use the orifice
provided on the breech plate;
2.
From a cold start, let the unit operate for about 5 minutes;
3.
Set the burner air setting until you have between 0 and 1 on the
Bacharach Scale (or a ‘’trace’’);
4. Take a CO
2
sample at the same test location where the #1
smoke reading was taken and make note of it. Example: 13.8%
of CO
2
or 2.5% of O
2
;
5.
Adjust the burner air setting to obtain a CO
2
reading 1.5% lower
(or an O
2
reading 2.0% higher) than the reading associated
with the ‘’trace’’ of smoke. Example: 12.3% of CO
2
or 4.5% of
O
2
;
6. This method of adjusting the burner will result in clean
combustion (Bacharach smoke scale between 0 and a ‘’trace’’)
and ensure the proper functioning of the system. The optimum
CO
2
level is around 12% to 13% (or 3.5% to 5.0% of O
2
).
2.3.4.
Draft Regulator adjustment
On chimney installations only, a barometric draft regulator (supplied
with the furnace) must be installed, in order to ensure proper draft
through the furnace. The barometric damper must be mounted with
the hinge pins in a horizontal position and the face of the damper
vertical for proper functioning (see instructions included with the
damper.) After the furnace has been firing for at least five minutes,
the draft regulator should be set to between -0.025" and -0.060"
W.C.
2.3.5.
Overfire pressure test
The overfire draft that is taken through the observation port, located
above the burner, is a measurement necessary to determine if there
is a blockage in the heat exchanger or the flue pipe. The overfire
pressure should be set between -0.035” to +0.025”W.C. for chimney
installation and +0.05” to +0.17”W.C. for direct vent installation. A
high pressure condition may be caused by excessive combustion
air, due to the air band being too wide open, or a lack of flue draft
(chimney effect) or some other blockage, such as soot in the
secondary section of the heat exchanger or the use of an oversize
nozzle input or high pressure pump.
2.3.6.
Vent Temperature Test
1. After having adjusted the burner combustion, insert a
thermometer into the test hole in the breech pipe;
Low flue gas temperatures increase the risk of
condensation. Adjust the total temperature at or
higher then 204°C (400°F) in order for the heat
exchanger warranty to remain in force.
2. The
total vent temperature should be between 204 and 302°C
(400 and 575°F). If not, check for improper air temperature rise,
pump pressure, nozzle size or a badly soothed heat exchanger.
2.3.7.
Supply Air Temperature Rise Test
1.
Operate the burner for at least 10 minutes;
2.
Measure the air temperature in the return air plenum;
3. Measuring the air temperature in the largest trunk coming off
the supply air plenum, just outside the range of radiant heat
from the heat exchanger. 0.3 m (12") from the plenum of the
main take-off is usually sufficient;
4. The temperature rise is calculated by subtracting the return air
temperature from the supply air temperature;
5. If the temperature rise is lower or exceeds the temperature
specified in Table 10, change to the next lower or higher blower
speed tap, until the temperature rise falls to the target. If the
excessive temperature rise cannot be increased or reduced by
changing fan speed, investigate for ductwork obstructions, dirty
or improper air filter, improper firing caused by improper pump
pressure or nozzle sizing.
2.3.8.
Limit Control Check
After operating the furnace for at least 15 minutes, restrict the return
air supply by blocking the filters or the return air register and allow
the furnace to shut off on High Limit. The burner will shut off but the
blower will continue to run.
Remove the obstruction and the burner should restart after a few
minutes. The time required for the restart also depends on the
adjustment of the blower “OFF” delay.
2.3.9.
Restart after Burner Failure
1.
Set the thermostat lower than room temperature;
2.
Press the reset button on the burner primary control (relay);
3.
Set the thermostat higher than room temperature;
4. If the burner motor does not start or ignition fails, turn off the
disconnect switch and CALL A QUALIFIED SERVICE
TECHNICIAN.
Do not attempt to start the burner when excess
oil has accumulated, when the furnace is full of
vapor or when the combustion chamber is hot.
