16
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
B-VENT GAS FIREPLACES (MPB33/35/40/45) • CARE AND OPERATION INSTRUCTIONS
BURNER ADJUSTMENTS
(QUALIFIED TECHNICIANS ONLY)
FLAME APPEARANCE AND SOOTING
Proper fl ame appearance is a fl ame which
is blue at the base and becomes yellowish-
orange in the body of the fl ame.
When the appliance is fi rst lit, the entire
fl ame may be blue and will gradually turn
yellowish-orange during the fi rst 15 minutes
of operation. If the fl ame remains blue, or if
the fl ame is orange with evidence of sooting
(black tip), the air shutter opening may need
to be adjusted.
If the air shutter opening is closed too far,
sooting may develop. Sooting is indicated
by black puffs developing at the tips of very
long orange fl ames. Sooting results in black
deposits forming on the logs, appliance
inside surfaces and on exterior surfaces
adjacent to the vent termination.
Sooting is caused by incomplete combustion
in the fl ames and lack of combustion air
entering the air shutter opening. To achieve
a warm yellowish-orange fl ame with an
orange body that does not soot, the shutter
opening must be adjusted between these two
extremes.
AIR SHUTTER ADJUSTMENT GUIDELINES
• If there is smoke or soot present, fi rst
check the log set positioning to ensure
that the fl ames are not impinging on
any of the logs. If the log set is properly
positioned and a sooting condition still
exists, then the air shutter opening should
be increased.
• The more offsets in the vent system, the
larger the air shutter opening is needed.
• An appliance operated with the air shutter
opened too far, may have fl ames that
appear blue and transparent. These weak,
blue, transparent fl ames are termed anemic.
• Propane models may exhibit fl ames
which candle or appear stringy. If this is
present and persists, adjust the air shutter
to a more closed position, then operate
the appliance for a few more minutes to
ensure that the fl ame normalizes and the
fl ames do not appear sooty.
The following chart is provided to aid you in
achieving the correct air shutter adjustment
for your installation.
Amount of
Primary Air
Flame
Color
Air Shutter
Adjustment
If air shutter is
closed too far
Flame will
be orange
Air shutter
gap should be
increased
If air shutter is
open too far
Flame will
be blue
Air shutter
gap should be
decreased
Table 6: Air Shutter Adjustment
Guidelines:
Figure 11: MPB33
Figure 12: MPB35
Figure 13: MPB40 and MPB45
