38
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
Burner Orifice Sizes
Elevation 0-4500 feet ( 0-1372 meters)
Model
Series
Nat.Gas
drill size (inches)
Propane
drill size (inches)
MPd33
#47 (0.0785")*
99K74 •
0.048"
99K78 •
MPd35
#44 (0.086")*
60J80 •
#55 (0.052")*
19L52 •
MPd40
#38 (0.102") *
99K76 •
0.062"
21L01 •
MPd45
#37 (0.104")*
24M10 •
#52 (0.0635")*
37G00 •
Table 10
* Standard size installed at factory
• Part /Cat. Number
Step 4.
Carefully remove the logs.
Exercise
care so as not to break the logs
.
Step 5.
Refer to
Figure 53, 54, or 55
.
A.
Remove the grate and sub floor.
B.
Remove the two (2) screws securing the
burner assembly.
C.
Remove the burner assembly with attached
venturi tube.
Millivolt and Electronic Ignition System
Appliances
Step 6.
SIT Systems
- Refer to
Figure 63
and the instructions provided with the SIT
Regulator Conversion Kit. Using a Torx T20
driver (with 1/4" shank and center hole) or
slotted screwdriver, remove and discard the
pressure regulator mounting screws (two
screws for electronic models, three screws
for millivolt models), pressure regulator tower,
the diaphragm assembly (if applicable) and
the spring. Discard all removed components.
Step 7.
Install the new pressure regulator as-
sembly using the supplied screws as shown
in
Figure 63
. Tighten the screws to 25 in-lb.
Figure 65: Orifice
Figure 63: Regulator Conversion
Pressure
Regulator
Remove
These
Components
Electronic Valve
Millivolt Valve
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 11.
Retrieve the burner and hold the
venturi tube above the orifice. Place the shutter
adjusting rod in the slot of the shutter arm (see
Figure 60
on
Page 34
). Set the burner assem-
bly into its position and secure the trapezoidal
plate with the two screws previously removed.
Step 12.
Reinstall the baffle with the two baffle
securing screws.
Step 13.
Reassemble the remaining compo-
nents by reversing the procedures outlined in
the
Steps 1-5
.
Step 14
. Attach the conversion label provided
in the conversion kit next to the rating plate on
the appliance.
Step 15
. Turn on gas supply and test for gas
leaks (refer to
Page 27
).
Step 16
. Relight the main burner. The lighting
instructions can be found on the lighting label
in the control compartment or in the Care and
Operation Manual provided with the appliance.
Verify proper burner ignition and operation. See
Burner Adjustments and Burner Flame Appear-
ance on
Page 33
.
Step 17.
Inspect the pilot system for proper
flame. The pilot flame should engulf the flame
sensor as shown in
Figures 49 and 50
on
Page 27
.
Step 18
. Using a manometer, test the inlet and
manifold gas pressures. See
Tables 2 and 3
on
Page 4
.
ALWAYS TEST PRESSURES WITH THE VALVE
REGULATOR CONTROL AT THE HIGHEST
SETTING.
Step 10.
Remove the orifice from the manifold
and replace it with the one provided in the kit.
See
Table 10
for orifice sizes for natural and
propane models.
Figure 65
illustrates the orifice.
Pilot
Orifice
Figure 64: Millivolt Pilot
(electronic pilot is similar)
Step 8.
Install the enclosed identification label
to the valve body where it can be easily seen.
Step 9.
Refer to
Figure 64
. Remove the pilot
hood assembly to access the hexed pilot orifice.
Remove and replace the orifice with the one
provided with the kit. Exercise extreme care to
prevent damage to or breakage of the igniter
assembly.
Printed in U.S.A. © 2012 Lennox Hearth Products LLC
P/N 506015-07 Rev. B 06/2013
Lennox Hearth Products reserves the right to make changes at any time, without notice, in
design, materials, specifications, and prices, and also to discontinue colors, styles, and products.
Consult your local distributor for fireplace code information.
LENNOX
®
, the LENNOX design, DAVE LENNOX, the image of DAVE LENNOX and other related
LENNOX marks are registered or common law trademarks of Lennox Industries Inc. and are
used with permission.
1508 Elm Hill Pike, Suite 108 • Nashville, TN 37210
