Bryant OBM098, Installation Instructions Manual

 12

CAUTION 

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. 

3.3.3 Combustion 

Check 

IMPORTANT

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. 

IMPORTANT

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 a 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

). 

3.3.4 

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. 

3.3.5 

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. Refer to the Technical Specifications in this manual 
for overfire pressure values. 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. 

3.3.6  Vent Temperature Test  

1. 

After having adjusted the burner combustion, insert a 
thermometer into the test hole in the breech pipe; 

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 sooted heat exchanger. 

3.3.7  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 6, 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. 

3.3.8  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. 

3.3.9  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. 

CAUTION 

Do not attempt to start the burner when excess oil has 
accumulated, when the furnace is full of vapour or when 
the combustion chamber is hot.