4
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
Test gauge connections are provided on the
front of the millivolt and electronic gas control
valve (identified IN for the inlet and OUT for
the manifold side). The control valves have a
3/8" (10 mm) NPT thread inlet and outlet side
of the valve (refer to
Figures 1 and 2
)
.
Propane tanks are at pressures that will cause
damage to valve components. Verify that the
tanks have step down regulators to reduce the
pressure to safe levels.
Orifice Sizes - Sea Level to High Altitude
(All Models)
These appliances are tested and approved for
installation at elevations of 0-4500 ft (0-1372
m) above sea level using the standard burner
orifice sizes (marked with an "*" in
Table 4
)
.
For elevations above 4500 ft, contact your gas
supplier or qualified service technician.
deration -
At higher elevations, the amount
of BTU fuel value delivered must be reduced
by either:
• Using gas that has been derated by the gas
company.
• Changing the burner orifice to a smaller size
as regulated by the local authorities having
jurisdiction and by the (USA) National Fuel
Gas Code NFPA 54 - latest edition / ANSI
Z223.1 or, in Canada, the CAN/CGA-B149.1
codes - latest edition.
Install the appliance according to the regulations
of the local authorities having jurisdiction and,
Fuel #
Low
High
Natural
Gas
1.6" WC
(0.40 kPa)
3.5" WC
(0.87 kPa)
Propane
6.3" WC
(1.57 kPa)
10.0" WC
(2.49 kPa)
Table 3: Manifold Gas Supply Pressure
The appliance and its appliance main gas
valve must be disconnected from the gas
supply piping system during any pressure
testing of that system at test pressures
in
excess of
1/2 psi (3.5 kPa).
The appliance must be isolated from the
gas supply piping system by closing its
equipment shutoff valve during any pressure
testing of the gas supply piping system at
test pressures
equal to or less than
1/2 psi
(3.5 kPa).
Fuel #
Minimum
Maximum
Natural
Gas
4.5" WC
(1.12 kPa)
10.5" WC
(2.61 kPa)
Propane
11.0" WC
(2.74 kPa)
13.0" WC
(3.23 kPa)
Table 2: Inlet Gas Supply Pressure
Gas Pressure - All Models
Tables 2 and 3
show the appliances' inlet and
manifold gas pressure requirements:
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 4
* Standard size installed at factory
• Part /Cat. Number
REQUIREMENTS FOR THE
COMMONWEALTH OF MASSACHUSETTS
These fireplaces are approved for installation in
the US state of Massachusetts if the following
additional requirements are met:
• Install this appliance in accordance with
Massachusetts Rules and Regulations 248
C.M.R.
• Installation and repair must be done by
a plumber or gas fitter licensed in the
Commonwealth of Massachusetts.
• The flexible gas line connector used shall
not exceed 36 (92 cm) in length.
• The individual manual shut-off must be a
T-handle type valve.
Massachusetts Horizontal Vent Requirements
in the Commonwealth of Massachusetts,
horizontal terminations installed less than
seven (7) feet above the finished grade
must comply with the following additional
requirements:
• A hard wired carbon monoxide detector
with an alarm and battery back-up must be
installed on the floor level where the gas
fireplace is installed. The carbon monoxide
detector must comply with NFPA 720, be
ANSI/UL 2034 listed and be ISA certified.
• A metal or plastic identification plate must be
permanently mounted to the exterior of the
building at a minimum height of eight (8) feet
above grade and be directly in line with the
horizontal termination. The sign must read,
in print size no less than one-half (1/2) inch
in size, GAS VENT DIRECTLY BELOW. KEEP
CLEAR OF ALL OBSTRUCTIONS.
in the USA, the National Fuel Gas Code NFPA
54 - latest edition / ANSI Z223.1 or, in Canada,
the CAN/CGA-B149.1
-
latest edition.
Flame breadth, height and width will diminish
4% for every 1,000 feet of altitude.
Gas Valve
diagrams
.
See
Figure 1
for Millivolt models
and
Figure 2
For Electronic Models.
In Canada - CAN/CGA-2.17-M91 (R2009)
(high altitude): THE CONVERSION SHALL
BE CARRIEd OUT BY A MANUFACTURER’S
AUTHORIZEd REPRESENTATIVE,IN
ACCORdANCE WITH THE REQUIREMENTS
OF THE MANUFACTURER, PROVINCIAL
OR TERRITORIAL AUTHORITIES HAVING
JURISdICTION ANd IN ACCORdANCE WITH
THE REQUIREMENTS OF THE CAN/CGA-B149.1
OR CAN/CGA-B149.2 INSTALLATION COdES.
H I
L O W
H T
P T
H T
P T
P I L O
T
P I
L O
T
O N
it
O F F
IN OUT
HI/LO Variable
Flame Height
Adjustment
Figure 1 - SIT Millivolt
Gas Valve
Manifold Pressure Tap
Inlet Pressure Tap
Pilot Adjustment
Screw
Main Gas Control Knob
OFF/PILOT/ON
Orange Wire
(from dFC Wire
Harness)
Main Gas Inlet
3/8" NPT
Green Wire
(from dFC Wire Harness)
Inlet (IN) Test Port
Manifold (OUT) Test Port
Figure 2 - SIT Electronic Gas Valve
Hi/Lo Flame
Control Knob
Yellow Ground Wire
(from dFC Wire Harness)
