10
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
PRE-INSTALLATION STEPS
The appliance is shipped with all gas controls
and components installed and pre-wired.
Before installing the appliance, follow these
steps:
1. Remove the shipping carton.
2. Remove the shipping pad, exposing the front
glass door.
3. Open the two spring latches securing the
glass door (under the fi rebox fl oor). Remove
the door by tilting it outward at the bottom
and lifting it up. Set the door aside, taking
care to protect it from inadvertent damage.
See Removing The Glass Enclosure Panel
on Page 32.
5. Remove the log set from the fi rebox. Handle
logs carefully to prevent breakage.
6. Remove the embers and volcanic stone from
the control compartment.
DETAILED INSTALLATION STEPS
Step 1. FRAMING
Frame the appliance as illustrated in Figures
12 and 13 on Pages 11 and 12 (Figure 13
applies to corner framing installations only).
All framing details must allow for a minimum
clearance to combustible framing members
as shown in Table 5 on Page 8.
If the appliance is to be elevated above fl oor
level, a solid continuous platform must be
constructed below the appliance.
Headers may be in direct contact with the
appliance top standoff spacers when they
are bent up vertically, maintaining the 3 in.
clearance to the fi replace top, but must not
be supported by them or notched to fi t
around them. All construction above the
appliance must be self-supporting. DO NOT
use the appliance for structural support.
Secure the fi replace to the side framing
members using the unit’s nailing fl anges
— one top and bottom on each side of the
fi replace front. See Figure 11. Use 8d nails
or their equivalent.
TYPICAL INSTALLATION SEQUENCE
The typical sequence of installation is
outlined below; however, each installation
is unique and may result in variations to the
steps described. See the pages referenced in
the following steps for detailed procedures.
Step 1. FRAMING (Page 10): Construct the
appliance framing. Position the appliance
within the framing and secure with nailing
brackets.
IMPORTANT! Bend up the appropriate
header spacing standoffs for the drywall/
fi nish material thickness to be used
(see Figure 11).
Bend up the outer pair for 1/2 in. materials
and the inner pair for 5/8 in. materials.
Bend out the appropriate nailing fl anges for
the drywall/fi nish material to be used. Nailing
fl anges are provided for fl ush framing, 1/2 in.
and 5/8 in. framing depths (see Figure 11).
Step 2. ROUTING GAS LINE (Page 12):
Route gas supply line to appliance location.
Step 3. PREPARING APPLIANCE VENT
COLLAR (MPD35/40/45 models with
combined top/rear vent) (Page 13).
Step 4. INSTALLING VENT SYSTEM
(Page 13): Install the vent system and
exterior termination.
Step 5. FIELD WIRING (Page 25).
a. Millivolt Appliances—Install the
operating control switch (not factory
provided). If installing the optional forced
air circulating blower, bring in electrical
service line.
b. Electronic Appliances—Field wire and
install operating control switch.
Step 6. WIRING—OPTIONAL FORCED AIR
BLOWER KIT (Page 26).
Step 7. CONNECTING GAS LINE (Page 26):
Make connection to gas supply.
Step 8. VERIFYING APPLIANCE OPERATION
(Page 27).
Step 9. INSTALL VOLCANIC STONE,
GLOWING EMBERS, AND LOGS (Page 28).
Step 10. INSTALLING GLASS DOOR
ASSEMBLY (Page 32).
Step 11. BURNER ADJUSTMENTS (Page 32):
Adjust burner to ensure proper fl ame
appearance.
Step 12. HOOD INSTALLATION (Page 34).
Step 13. ATTACHING SAFETY-IN-
OPERATION WARNINGS
(Page 35).
IMPORTANT!
Bend up the appropriate header spacing top
standoffs before installing the fi replace.
Figure 11: Unit Secured to Framing by
Nailing Flange
NOTE: The nailing fl anges, combustible
members, and screw heads in areas directly
adjacent to the nailing fl anges are EXEMPT
from the 1/2 in. clearance to combustible
requirements for the fi rebox outer wrapper.
Combustible framing may be in direct contact
with the nailing fl anges and may be located
closer than 1/2 in. from screw heads and the
fi rebox wrapper in areas adjacent to the
nailing fl anges.
Frame the opening to the exact dimensions
specifi ed in the framing details in this manual.
Side
Framing
Unit Nailing Flange
(No clearance to
combustible framing
is required)
Header Spacing Top Standoffs
(two pairs on front edge of firebox top)
Lift up outer pair for
1/2 in. finish materials
Lift up inner pair for
5/8 in. finish materials
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