13
NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.
LENNOX HEARTH PRODUCTS • MERIT PLUS
®
DIRECT VENT GAS FIREPLACES (MPD33/35/40/45) • INSTALLATION INSTRUCTIONS
Use only approved vent components (see
Approved Vent Components on Page 2).
These fi replaces must be vented
directly to the outside.
The vent system may not service multiple
appliances, and must never be connected to
a fl ue serving a separate solid fuel burning
appliance. The vent pipe is tested to be run
inside an enclosed wall (such as a chase).
There is no requirement for inspection
openings in the enclosing wall at any of the
joints in the vent pipe.
Installation of Vent Restrictor
A vent restrictor may be needed with this
appliance, install vent restrictor (provided)
in the appliance top fl ue outlet as shown
in Figure 17 (MPDT33, MPD35, MPD40
and MPD45) or rear fl ue outlet as shown in
Figure 18 (MPD35, MPD40 and MPD45). It
is held in place by friction, only.
Note: The vent restrictor is included in the
fi rebox.
Step 3. PREPARING APPLIANCE VENT
COLLAR (MPD35/-40/-45 models with
combined top/rear vent)
Each of the unit’s two vent collars are sealed
with a cover plate and a seal plate and
gasket. The cover, and seal plate and gasket
must be removed from the vent collar being
used. Refer to Figure 15 for top vent usage
and Figure 16 for rear, and the following
steps to prepare the appropriate collar
for use.
From the vent collar being used, remove the
four screws securing the vent seal plate and
gasket. Remove and discard the seal plate and
gasket.
When the top vent collar is being used,
from inside the fi rebox, loosen the two
screws in the keyhole slots of the cover plate
and remove the remaining two cover plate
securing screws. Remove and discard the
cover plate. Reinstall and securely tighten
all four screws.
When the rear vent collar is being used,
from inside the fi rebox, remove the two
screws securing the lintel to the rear wall of
the fi rebox, then remove the lintel. Remove
the four cover plate securing screws. Remove
and discard the cover plate.
Reinstall and securely tighten all four cover
plate screws. Re-secure the lintel to the rear
wall of the fi rebox.
Figure 17: Vent restrictor installation—
Top vent
Figure 15: Top vent seal and cover plate
removal—MPD35/40/45 series models
(combined top and rear vent units)
Step 4. INSTALLING VENT SYSTEM
These instructions should be used as a
guideline and do not supersede local
codes in any way. Install venting according
to local codes, these instructions,
the current National Fuel Gas Code
(ANSI-Z223.1-2009) in the USA or the
current standards of CAN/CSA-B149.1
in Canada.
Ensure clearances are in accordance
with local installation codes and the
requirements of the gas supplier.
Dégagement conforme aux codes
d'installa tion locaux et aux exigences du
foumisseunde gaz.
Select Venting System—Horizontal or
Vertical
With the appliance secured in framing,
determine vent routing and identify the
exterior termination location. The following
sections describe vertical (roof) and horizontal
(exterior wall) vent applications. Refer to the
section relating to your installation. A list of
approved venting components are shown on
Pages 36 and 37.
A vent restrictor may be needed when
vertically terminating the vent system above
the roof (when using the appliance top vent),
install vent restrictor in the top vent of the
fireplace outlet on MPD35/40/45
and MPDT33 series models.
U-SHAPED VENT
RESTRICTOR
APPLIANCE TOP
VENT OUTLET
If needed, install the restrictor orientated as
shown, either from inside or outside the unit,
in the inner fireplace collar.
INNER
FIREPLACE
COLLAR
U-SHAPED VENT
RESTRICTOR
APPLIANCE REAR
VENT OUTLET
A vent restrictor may be needed when
horzontally terminating the vent system from
the rear of the appliance (when using the
appliance rear vent), install vent restrictor in
the rear vent of the fireplace outlet on
MPD35/40/45 series models, in any
installation that has a vertical vent run in
excess of three feet (0.914 meters).
INNER FIREPLACE
COLLAR
If needed, install the restrictor orientated as
shown, either from inside or outside the unit,
in the inner fireplace collar.
Figure 16: Rear vent seal and cover
plate removal—MPD35/40/45 series
models (combined top and rear vent units)
Figure 18: Vent restrictor installation—
Rear vent
KNOCKOUT
GASKET
FIREBOX TOP
CABINET TOP
VENT
COVER PLATE
TOP VENT
COVER PLATE
SECURING SCREWS
CROSS SECTION
(INSIDE UNIT)
(OUTSIDE UNIT)
KNOCKOUT
CAP AND
GASKET
CROSS SECTION
REAR VENT
COVER PLATE
SECURING SCREWS
CABINET BACK
(INSIDE UNIT)
(OUTSIDE UNIT)
WARNING
Failure to reinstall and securely
tighten cover plate screws could
result in leakage of fl ue products
into the living space. Vent cover
plate and vent seal cap must
remain securely installed on
unused vent collar. Failure to
do so could result in leakage of
fl ue products into living space.
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