11
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPDP35/40) • INSTALLATION INSTRUCTIONS
FIREPLACE FRAMING SPECIFICATIONS
Schedule 40
Black Iron Pipe
Inside Diameter (Inches)
Schedule 40 Pipe
Length (feet)
Natural
Gas
Propane
Gas
0-10 1/2 3/8
10-40 1/2 1/2
40-100 1/2 1/2
100-150 3/4 1/2
150-200 3/4 1/2
Table 6
Notes:
• All appliances are factory-equipped with
a flexible gas line connector and 1/2 inch
shutoff valve (see Figure 52 on Page 28).
• See Massachusetts Requirements on Page
4 for additional requirements for installations
in the state of Massachusetts in the USA.
• The gas supply line should Not be connected
to the appliance until Step 7 on Page 28.
• A pipe joint compound rated for gas should be
used on the threaded joints. Ensure propane
resistant compounds are used in propane
applications. Be very careful that the pipe
compound does not get inside the pipe.
• It is recommended to install a sediment trap
in the supply line as close as possible to the
appliance.
• Check with local building official for local
code requirements (i.e. are below grade
penetrations of the gas line allowed?, etc).
IMPORTANT: If propane is used, be aware that
if tank size is too small (i.e. under 100-lbs, if
this is the only gas appliance in the dwelling.
Ref. NPFA 58), there may be loss of pressure,
resulting in insufficient fuel delivery (which
can result in sooting, severe delayed ignition
or other malfunctions). Any damage resulting
from an improper installation, such as this,
is not covered under the limited warranty.
Proper Sizing of Gas Line
Properly size and route the gas supply line
from the supply regulator to the area where the
appliance is to be installed per requirements
outlined in the National Fuel Gas Code, NFPA
54 - latest edition (USA) or CAN/CSA-B149.1
- latest edition (Canada).
Step 2. ROUTING GAS LINE
Route a 1/2" (13 mm) gas line to the left side
of the appliance as shown in Figure 14. Gas
lines must be routed, constructed and made
of materials that are in strict accordance with
local codes and regulations. All appliances
are factory-equipped with a flexible gas line
connector and 1/2-inch shutoff valve (see Step
7 on Page 28).
Never use galvanized or plastic pipe. Refer to
Table 6 for proper sizing of the gas supply line,
if black iron pipe is being used. Gas lines must
be routed, constructed and made of materials
that are in strict accordance with local codes
and regulations. We recommend that a quali-
fied individual such as a plumber or gas fitter
be hired to correctly size and route the gas
supply line to the appliance. Installing a gas
supply line from the fuel supply to the appliance
involves numerous considerations of materials,
protection, sizing, locations, controls, pressure,
sediment, and more. Certainly no one unfamil-
iar and unqualified should attempt sizing or
installing gas piping.
Figure 13: Corner Framing with Horizontal Termination
Also see Figure 12.
Figure 14: Route Gas Line
3"
(76 mm)
Left Side Front
Corner of Fireplace
Framing
6-1/2"
(152 mm)
Pipe Coupling
(Recommended)
Note:
• Rear Vent Applications in Corner Installations: The horizontal vent length
(from
a
to
b
) must not exceed 28 inches (711 mm).
• MPDP35 and MPDP40: Dimensions D through F apply when one 45-degree
elbow is connected directly to the appliance collar.
C
Back wall of chase/enclosure (including any finishing materials)
7"
(178 mm)
D
E
F
A
B
b
a
Top Vent
Rear Vent
Model No. A B C D E F
MPDP35
in. 35-1/8 57-1/2 40-5/8 19-3/16 28-3/4 6-1/8
mm 892 1461 1032 487 730 156
MPDP40
in. 40-1/8 61-3/16 43-11/32 19-3/16 30-11/16 7-7/8
mm 1019 1554 1101 487 779 200
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