4
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
B-VENT GAS FIREPLACES (MPB33/35/40/45) • 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/ANSI Z223.1 - latest
edition or, in Canada, the CAN/CGA-B149.1
codes - latest edition.
Fuel #
Low
High
Natural Gas
2.2" WC
(0.55 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 pres-
sures 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
(2.62 kPa)
Propane
11.0" WC
(2.74 kPa)
13.0" WC
(3.24 kPa)
Table 2 - Inlet Gas Supply Pressure
GAS PRESSURE - ALL MODELS
Tables 2 and 3
show the appliances' inlet and
manifold gas pressure requirements:
REqUIREMENTS FOR THE COMMON-
WEALTH 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 Com-
monwealth of Massachusetts.
• The flexible gas line connector used shall
not exceed 36 inches (92 centimeters) in
length.
• The individual manual shut-off must be a
T-handle type valve.
Cold Climate Insulation
For cold climate installations, seal all cracks
around your appliance with noncombustible
material and wherever cold air could enter
the room. It is especially important to insulate
outside chase cavity between studs and under
floor on which appliance rests, if floor is above
ground level. Gas line holes and other openings
should be caulked or stuffed with unfaced
fiberglass insulation.
Install the appliance according to the regulations
of the local authorities having jurisdiction and,
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 MANUFACTUR-
ER’S AUTHORIzED REPRESENTATIVE,
IN ACCORDANCE WITH THE REqUIRE-
MENTS OF THE MANUFACTURER, PRO-
VINCIAL OR TERRITORIAL AUTHORITIES
HAVING JURISDICTION AND IN ACCOR-
DANCE WITH THE REqUIREMENTS OF
THE CAN/CGA-B149.1 OR CAN/CGA-
B149.2 INSTALLATION CODES.
H I
LO
W
HT
PT
HT
PT
PILO
T
PI
LO
T
ON
it
OFF
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)
Burner Orifice Sizes
Elevation 0-4500 feet ( 0-1372 meters)
Model
Nat.Gas
drill size (inches)
Propane
drill size (inches)
MPB33
#47 (0.0785")*
99K74 •
(0.048")*
99K78 •
MPB35
#44 (0.086")*
60J80 •
#55 (0.052")*
19L52 •
MPB40
#38 (0.102")*
99K76 •
(0.062")*
21L01 •
MPB45
#37 (0.104")*
24M10 •
#52 (0.0635")*
37G00 •
Table 4
* Standard size installed at factory
• Part /Cat. Number
