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NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT
®
PLUS DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
Retaining
Clip
Ignitor
Assembly
Pilot
Assembly
Pilot
Orifice
Flare Nut
See Figure 71 and replace the pilot orifice as
follows: Remove the ignitor assembly retainer
clip, and carefully remove the ignitor assembly.
Exercise extreme care to prevent damage to
or breakage of the ignitor assembly. Remove
the screw securing the pilot assembly to its
mounting bracket. Back off the flare nut at
the end of the pilot gas line to free the pilot
assembly from the gas line. Remove the pilot
orifice and replace it with the one provided with
the conversion kit. Reinstall the pilot assembly
by reversing the steps detailed here.
When reinstalling the ignitor assembly, use
extreme care to prevent damage and break-
age. Do not apply any leverage to the ignitor
assembly while restoring the retainer clip to
its original position.
Figure 71
Step 9. Reassemble the remaining components
by reversing the procedures outlined in the
preceding steps.
Step 10. Attach the conversion label provided
in the conversion kit next to the rating plate on
the appliance.
Step 11. Turn on gas supply and test for gas
leaks (refer to page 27).
All Models
Use pipe joint compound or Teflon tape on all
pipe fittings before installing (ensure propane
resistant compounds are used in propane ap-
plications, do not use pipe joint compounds
on flare fittings).
Step 8. (Refer to Figure 67 on page 39 )
A. Remove the orifice from the manifold and
replace it with the one provided in the kit. See
the following table for orifice sizes for natural
and propane models. Figure 72 illustrates
the orifice.
B. Retrieve the burner and hold the venturi tube
above the orifice . Place the shutter adjusting
rod in the propane slot of the shutter arm (see
Figure 64 on page 34 ). Set the burner assem-
bly into its position and secure the trapezoidal
plate with the two screws previously removed.
C. Reinstall the baffle with the two baffle
securing screws.
Figure 72
Note: If the ignitor is damaged, a replacement
kit is available, order Catalog Number 87L54.
Burner Orifice Sizes
Elevation 0-4500 feet ( 0-1372 meters)
Model
Series
Nat.Gas
drill size (inches)
Propane
drill size (inches)
MPDT-3328
MPDR-3328
#45 (0.0820")*
39L66•
0.048 inch
99K78•
MPD-3530
#44 (0.0860")*
60J80•
#55 (0.0520")*
19L52•
MPD-4035
#37 (0.1040")*
24M10•
0.063 inch
21L01•
MPD-4540
#36 (0.1065")*
18L40•
#52 (0.0635")*
37G00•
Table 9
* Standard size installed at factory
• Part /Cat. Number