Lennox MLDVT-40PM, MLDVT-35NM, MLDVT-30NM, MLDVT-45NE, MLDVT-30PM User Manual

INSTALLATION INSTRUCTIONS

AVERTISSEMENT : Assurez-vous de bien suivre les
instructions données dans cette notice pour réduire au
minimum le risque d’incindie ou d’explosion ou pour
éviter tout dommage matériel, toute blessure ou la mort.

WARNING: If the information in these instructions
is not followed exactly, a fire or explosion may
result, causing property damage, personal injury,
or death.

WARNING /AVERTISSEMENT/AVISO

• HOT GLASS WILL CAUSE
BURNS.

• DO NOT TOUCH GLASS
UNTIL COOLED.

• NEVER ALLOW CHILDREN
TO TOUCH GLASS.

• UNE SURFACE VITRÉE CHAUDE
PEUT CAUSER DES BRÛLURES.

• LAISSER REFROIDIR LA SURFACE
VITRÉE AVANT D'Y TOUCHER.

• NE PERMETTEZ JAMAIS À UN ENFANT
DE TOUCHER LA SURFACE VITRÉE.

• EL VIDRIO CALIENTE
CAUSARÁ QUEMADURAS.

• USTED DEBE NUNCA
TOCAR EL VIDRIO CALIENTE.

• LOS NIÑOS DEBEN NUNCA
TOCAR EL VIDRIO.

- Do not store or use gasoline or other flammable

vapors and liquids in the vicinity of this or any other
appliance.

- WHAT TO DO IF YOU SMELL GAS:

• Do not try to light any appliance.

• Do not touch any electrical switch; do not use any

phone in your building.

• Immediately call your gas supplier from a

neighbor’s phone. Follow the gas supplier’s
instructions.

• If you cannot reach your gas supplier, call the fire

department.

- Installation and service must be performed by a
qualified installer, service agency or the gas supplier.

- Ne pas entreposer ni utilizer d’essence ni d’autres vapeurs
ou liquides inflammables dans le voisinage de cet appareil
ou de tout autre appareil.

- QUE FAIRE SI VOUS SENTEZ UNE ODEUR DE GAZ :

• Ne pas tenter d’allumer d’appareil.

• Ne touchez à aucan interrupteur. Ne pas vous servir des

téléphones se trouvant dans le bâtiment où vous trouvez.

• Appelez immédiatement votre fournisseur de gaz depuis

un voisin. Suivez les instructions du fournisseur.

• Si vous ne pouvez rejoindre le fournisseur de gaz,

appelez le service des incindies.

- L’installation et l’entretien doivent être assurés par un
installateur ou un service d’entretien qualifié ou par le
fournisseur de gaz.

MLDVT Direct-Vent
Gas Fireplaces

P/N 506015-02 Rev. E 06/2011

This manual is one of a set of two supporting this product.
Refer to P/N 506017-01 for Care and Operation Instructions.

Ce manuel est disponible en francais, simplement
en faire la demande. Numéro de la pièce 506223-03.

INSTALLER: Leave this manual with the appliance.
CONSUMER: Retain this manual for future reference.

INSTALLATEUR : Laissez cette notice avec l'appareil.
CONSOMMATEUR : Conservez cette notice pour
consultation ultérieure.

This appliance may be installed in an aftermarket permanently located, manufactured home (USA only) or mobile
home, where not prohibited by local codes. This appliance is only for use with the type of gas indicated on the rating
plate. This appliance is not convertible for use with other gases unless a certified kit is used.

MODELS

MILLIVOLT:

MLDVT-30NM
MLDVT-30PM
MLDVT-35NM
MLDVT-35PM

Report No. 100326540PRT-001

MLDVT-40NM
MLDVT-40PM
MLDVT-45NM
MLDVT-45PM

™

ELECTRONIC:

MLDVT-30NE
MLDVT-35NE
MLDVT-40NE
MLDVT-45NE

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

TABLE OF CONTENTS

Packaging .........................................Page 2

Introduction ......................................Page 2

General Information ..........................Page 2

Requirements for the
Commonwealth of Massachusetts .Page 4

New York City Approval .....................Page 4

Cold Climate Insulation .....................Page 5

Manufactured Home Requirements ..Page 5

Location ............................................Page 5

Vent Termination Clearances ............Page 6

Appliance and Vent Clearances .........Page 8

Pre-Installation Steps ........................Page 9

Typical Installation Sequence ...........Page 9

Detailed Installation Steps .................Page 9

Step 1. Framing ................................. Page 9

Fireplace/Framing Specifications .......Page 10

Step 2. Routing Gas Line ..................Page 11

Step 3. Install the Venting System ....Page 12

Vertical Termination Systems ............Page 13

Vent Section Length Chart ................Page 13

Vertical Vent Tables and Figures ........Page 16

Horizontal Termination System .........Page 17

Horizontal Vent Tables and Figures ...Page 20

Venting Using Flexible Vent Pipe .......Page 23

Step 4. Field Wiring .........................Page 24

Step 5. Optional Blower Kit Wiring ..Page 25

Step 6. Connecting Gas Line ...........Page 26

Step 7. Verifying Appliance Operation Page 27

Step 8. Installing Logs ...................Page 28

Step 9. Installing Glass Door ..........Page 31

Step 10. Burner Adjustments ............Page 31

Step 11. Hood Installation .................Page 33

Finishing Requirements ....................Page 33

Step 12. Attaching Safety-in-

Operation Warnings .......................Page 34

Installation Accessories ....................Page 35

Gas Conversion Kits .........................Page 37

Please read and understand these
instructions before beginning your

installation.

PACKAGING

The assembled vented gas fireplace heater is
packaged with:

• One log set located in firebox area.

• One envelope containing the literature pack-

age which consists of the care and operations
manual, installation instructions, safety in
operation warning labels and warranty; en­velope is located in the control compartment.

• One vent restrictor to be applied as shown on

Page 12 ; restrictor is taped to the envelope.

• One hood located behind the door assembly.

• One bag of decorative volcanic stone located

in the control compartment.

• One bag of glowing embers located in the

control compartment.

INTRODUCTION

The Millivolt appliances have a millivolt gas
control valve with piezo ignition system. If any
optional accessories that will require electrical
power are to be installed, the electrical power
must be provided at the time of appliance in­stallation.

The Electronic appliances have an electronic
intermittent pilot ignition system. External
electrical power is required to operate these
units. The battery back-up can be used in case
of a power outage.

These vented gas fireplace heaters are sealed
combustion, air-circulating gas fireplaces de­signed for residential applications.

Use Only These Approved Vent Components

These fireplaces are designed, tested and
listed for operation and installation with, the

following (4-1/2" inner and 7-1/2" outer) vent

components only:

• Secure Vent™ Direct-Vent System Compo-

nents manufactured by Security Chimneys
International,

• Secure Flex™ Flexible Vent Components

manufactured by Security Chimneys Inter­national and

• Z-FLEX™ Model GA Venting Systems listed

to UL1777 and ULCS635 manufactured by

Flexmaster Canada Limited.

These approved vent system components are
labeled for identification. DO NOT use any
other manufacturer’s vent components with
these appliances.

GENERAL INFORMATION

WARNING

Young children should be care­fully supervised when they are
in the same room as the appli­ance. Toddlers, young children
and others may be susceptible
to accidental contact burns. A
physical barrier is recommended
if there are at risk individuals in
the house. To restrict access to
a fireplace or stove, install an
adjustable safety gate to keep
toddlers, young children and
other at risk individuals out of
the room and away from hot
surfaces.

AVERTISSEMENT

Les jeunes enfants devraient être
surveillés étroitement lorsqu’ils
se trouvent dans la même pièce
que l’appareil. Les tout petits,
les jeunes enfants ou les adultes
peuvent subir des brûlures s’ils
viennent en contact avec la sur­face chaude. Il est recommandé
d’installer une barrière physique
si des personnes à risques habi­tent la maison. Pour empêcher
l’accès à un foyer ou à un poêle,
installez une barrière de sécu­rité; cette mesure empêchera les
tout petits, les jeunes enfants et
toute autre personne à risque
d’avoir accès à la pièce et aux
surfaces chaudes.

Children and adults should be alerted to the
hazards of high surface temperature and
should stay away to avoid burns or clothing
ignition.

Les enfants et les adultes devraient être
infor-més des dangers que posent les
températures de surface élevées et se
tenir à distance afin d’éviter des brûlures
ou que leurs vêtements ne s’enflamment.

DO NOT ATTEMPT TO ALTER OR MODIFY
THE CONSTRUCTION OF THE APPLIANCE
OR ITS COMPONENTS. ANY MODIFICATION
OR ALTERATION MAY VOID THE WARRANTY,
CERTIFICATION AND LISTINGS OF THIS UNIT.

2

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

WARNING

Improper installation, adjust­ment, alteration, service or
maintenance can cause injury
or property damage. Refer to
this manual. For assistance or
additional information consult
a qualified installer, service
agency or the gas supplier.

WARNING

Failure to comply with these
installation instructions will result
in an improperly installed and
operating appliance, voiding its
warranty. Any change to this appli­ance and/or its operating controls
is dangerous.

WARNING

Clothing or other flammable
material should not be placed
on or near the appliance.

AVERTISSEMENT

On ne devrait pas placer de
vêtements ni d’autres matières
inflammables sur l’appareil ni à
proximité.

WARNING

Any safety screen or guard
removed for servicing the appli­ance must be replaced prior to
operating the appliance.

AVERTISSEMENT

Tout écran ou protecteur retiré
pour permettre l’entretien de
l’appareil doit être remis en
place avant de mettre l’appareil
en marche.

WARNING

Improper installation or use of
this appliance can cause serious
injury or death from fire, burns,
explosion or carbon monoxide
poisoning.

Note: Installation and repair should be done
by a qualified service person. The appliance
should be inspected before use and at least
annually by a professional service person.
More frequent cleaning may be required due
to excessive lint from carpeting, bedding
material, etcetera. It is imperative that control
compartments, burners and circulating air
passageways of the appliance be kept clean.

Remarque : L’installation et la réparation
devrait être confiées à un technicien qualifié.
L’appareil devrait faire l’objet d’une inspec­tion par un technicien professionnel avant
d’être utilisé et au moins une fois l’an par la
suite. Des nettoyages plus fréquents peuvent
être nécessaires si les tapis, la literie, et
cetera produisent une quantité importante de
pous-sière. Il est essentiel que les comparti­ments abritant les commandes, les brûleurs et
les conduits de circulation d’air de l’appareil
soient tenus propres.

Do not use these appliances if any part
has been under water. Immediately call a
qualified, professional service technician
to inspect the appliance and to replace
any parts of the control system and any
gas control which have been under water.

Ne pas utiliser cet appareil s’il a été plongé,
même partiellement, dans l’eau. Ap­peler un technicien qualifié pour inspecter
l’appareil et remplacer toute partie du
système de commande et toute commande
qui a été plongée dans l’eau.

Only trim kit(s) supplied by the manufacturer
shall be used in the installation of this ap­pliance.

Seules les trousses de garniture fournies
par le fabricant doivent être utilisées pour
l’installation de cet appareil.

These appliances comply with National Safety
Standards and are tested and listed by ETL/

Intertek (Report No. 100326540PRT-001) to
ANSI Z21.88 (in Canada, CSA-2.33), and CAN/
CGA-2.17-M91 in both USA and Canada, as

vented gas fireplace heaters.

Both millivolt and electronic versions of
these appliances are listed by ETL/Intertek
for installation in bedrooms and Manufac­tured Homes.

Misc. Codes/Standards

The Installation must conform to local codes or,
in the absence of local codes, with the National

Fuel Gas Code, ANSI Z223.1/NFPA 54 - latest
edition (In Canada, the current CAN/CSA-B149.1

installation code).

The appliance, when installed, must be electri­cally grounded and wired in accordance with
local codes or, in the absence of local codes,
with the National Electrical Code, ANSI/NFPA

70 - latest edition, or the Canadian Electrical
Code, CSA C22.1 - latest edition.

Provide adequate clearances around air open­ings and adequate accessibility clearance for
service and proper operation. Never obstruct
the front or back openings of the appliance.

These appliances are designed to operate on
natural or propane gas only. The use of other
fuels or combination of fuels will degrade
the performance of this system and may be
dangerous.

These fireplaces are designed as supplemental
heaters. Therefore, it is advisable to have an
alternate primary heat source when installed
in a dwelling.

These appliances must not be connected to a
chimney or flue serving a separate solid fuel
burning appliance.

Millivolt Models - The millivolt appliances are
manually controlled and feature a spark igniter

(piezo) that allows the appliance's pilot gas to

be lit without the use of matches or batteries.
This system provides continued service in the
event of a power outage.

Millivolt models come standard with a manually-

modulated gas valve; flame appearance and heat
output can be controlled at the gas valve. The BTU
Input for these appliances is shown in Table 1.

Electronic Models - These electronic appli­ances are manually controlled and feature an
electronic intermittent pilot ignition system.
External electrical power is required to operate
these units.

These electronic models come standard with a
manually-modulated gas valve; flame appear­ance and heat output can be controlled at the
gas valve. The BTU Input for these appliances
is shown in Table 1.

Input (BTU/HR) Manually Modulated

Gas Valves (all models)

Models

MLDVT-30

MLDVT-35

MLDVT-40

MLDVT-45

Input Rate (BTU / HR)

Nat. Gas Prop. Gas

13,500 high

10,500 low

16,000 high

12,500 low

20,000 high

15,500 low

23,000 high

17,500 low

12,500 high

9,000 low

15,000 high

11,500 low

20,000 high

15,800 low

22,000 high

17,000 low

Table 1

3

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

Gas Pressure - All Models
Tables 2 and 3 show the appliances' inlet and

manifold gas pressure requirements:

Inlet Gas Supply Pressure

(all models)

Fuel # Minimum Maximum

Natural Gas

Propane

4.5" WC

(1.12 kPa)

11.0" WC

(2.74 kPa)

10.5" WC

(2.61 kPa)

13.0" WC

(3.23 kPa)

Table 2

Manifold Gas Supply Pressure

(all models)

Fuel # Low High

Natural

Gas

Propane

(Lo) 2.2" WC

(0.55 kPa)

(Lo) 6.3" WC

(1.57 kPa)

(Hi) 3.5" WC

(0.87 kPa)

(Hi) 10.0" WC

(2.49 kPa)

Table 3

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"
(10mm) 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.

These appliances must be isolated from the
gas supply piping system (by closing their

individual manual shut-off valve) during any

pressure testing of the gas supply piping
system at test pressures equal to or less

than 1/2 psig (3.5 kPa).

These appliances and their individual shut-off
valves must be disconnected from the gas
supply piping system during any pressure
testing of that system at pressures greater

than 1/2 psig (3.5 kPa).

Orifice Sizes - Sea Level to High Altitude
(All Models)

These appliances are tested and approved for

installation at elevations of 0-4500 feet (0-1372
meters) above sea level using the standard
burner orice sizes (marked with an "*" in Table

4). For elevations above 4500 feet, 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 orice 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/CSA-B149.1

codes - latest edition.

Install the appliance according to the regulations
of the local authorities having jurisdiction and,
in the USA, the National Fuel Gas Code NFPA

54 / ANSI Z223.1 - latest edition or, in Canada,
the CAN/CSA-B149.1 - latest edition.

NOTE: Flame appearance will diminish 4% per
thousand feet.

Burner Orifice Sizes

Elevation 0-4500 feet ( 0-1372 meters)

Model

Series

MLDVT-30

MLDVT-35

MLDVT-40

MLDVT-45

Nat.Gas

drill size (inches)

#50 (0.070")*

•

H4873

(0.0748")*

•

H1355

#44 (0.086")*

•

60J80

(0.090")*

•

37L70

Propane

drill size (inches)

#59 (0.041")*

•

H7838

(0.045")*

•

75L10

#55 (0.052")*

•

19L52

#54 (0.055")*

•

99K79

*Standard size installed at factory.
Table 4

Gas Valve Diagrams

See Figure 1 for Millivolt models and Figure 2
For Electronic Models.

Main Gas Control Knob

•

Part /Cat. Number.

OFF/PILOT/ON

N

O

T

O

t
i

L

I

P

O

F

F

Pilot Adjustment

W

O

L

H

I

Screw

T

O

L

I

P

H T P T H T P T

Supply
Gas
Inlet

Pressure-Tap
(Manifold)

IN

PILOT

Pilot Gas
Outlet

Regulator
Mounting Screw

Pressure-Tap
(Inlet)

Burner Stage

Terminal

VENT

OUT

IN

HI

Ground
(TP)

LO

TH

TH

TP

Pilot Stage
Terminal

TP

Figure 2 - Dexen Electronic Gas Valve

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 Com-

monwealth of Massachusetts.

• The exible 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.

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 certied.

• A metal or plastic identication 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.

NEW YORK CITY, NEW YORK (MEA)

Installation of these fireplaces are approved
for installation in New York City in the US state
of New York.

OUT

IN

Manifold Pressure Tap

Inlet Pressure Tap

HI/LO Variable
Flame Height
Adjustment

Figure 1 - SIT Millivolt Gas Valve

4

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

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.

If the fireplace is being installed on a cement
slab in cold climates, a sheet of plywood or
other raised platform can be placed underneath
to prevent cold transfer to the fireplace and into
the room. It also helps to sheetrock inside
surfaces and tape for maximum air tightness
and caulk firestops.

MANUFACTURED HOME
REQUIREMENTS

This appliance may be installed in an aftermarket
permanently located, manufactured home and
must be installed in accordance with the manu-

facturer's instructions and the Manufactured

Home Construction and Safety Standard, Title

24 CFR, Part 3280, in the United States, or the
Standard for Installation in Mobile Homes, CAN/
CSA Z240 MH Series, in Canada.

Cet appareil peut être installé cómme

du matéri-el d'origine dans une maison
préfabriquée (É.U. seulement) ou mobile

et doit être installé selon les instructions
du fabricant et conformément à la norme

Manufactured Home Constructions and
Safety, Title 24 CFR, Part 3200 aux Unis
ou à la norme Can/CSA-Z240 Série MM,
Maisons mobiles au Canada.

This appliance is only for use with the type of gas
indicated on the rating plate. This appliance is
not convertible for use with other gases, unless
a certified kit is used.

Cet appareil doit être utilisé uniquement
avec le type de gaz indiqué sur la plaque
signalétique. Cet appareil ne peut être

converti à d'autres gaz, sauf si une trousse

de conversion est utilisée.

CAUTION: Ensure that the cross mem­bers are not cut or weakened during
installation. The structural integrity of
the manufactured home floor, wall, and
ceiling / roof must be maintained.

CAUTION: This appliance must be ground­ed to the chassis of the manufactured
home in accordance with local codes or
in the absence of local codes, with the
National Electrical Code ANSI / NFPA 70

- latest edition or the Canadian Electrical
Code CSA C22.1 - latest edition.

TNEVPOT

NOITACILPPA

NOITACILPPA

TNEVPOT

NOITACILPPA

TNEVPOT

APPLICATION

TOP VENT

RECESSED

INSTALLATION

HORIZONTAL VENT

(Top Vent Application)

NOITACILPPA

TNEVPOT

TOP VENT

APPLICATION

VERTICAL VENT

(Top Vent Application)

Figure 3 - Typical Locations

LOCATION

In selecting the location, the aesthetic and
functional use of the appliance are primary
concerns. However, vent system routing to
the exterior and access to the fuel supply are
also important.

Due to high temperatures, the appliance
should be located out of traffic and away from
furniture and draperies (Figure 3).

En raison des températures élevées,
l’appareil devrait être installé dans un
endroit où il y a peu de circulation et loin
du mobilier et des tentures (Figure 3).

The location should also be free of electrical,
plumbing or other heating/air conditioning
ducting.

These direct-vent appliances are uniquely
suited for installations requiring a utility shelf
positioned directly above the fireplace. Util­ity shelves like these are commonly used for
locat-ing television sets and decorative plants.

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

Note: When the unit is installed with one
side flush with a wall, the wall on the other
side of the unit must not extend beyond the
front edge of the unit.

Be aware that this is a heat producing
appliance. Objects placed above the unit are
exposed to elevated temperatures.

Do not insulate the space between the
appliance and the area above it (see Figure
8 on Page 8).

The minimum height from the base of the appli­ance to the underside of combustible materials
used to construct a utility shelf in this fashion
is shown in Figure 8 on Page 8.

The appliance should be mounted on a fully
supported base extending the full width and
depth of the unit. The appliance may be located
on or near conventional construction materials.
However, if installed on combustible materials,
such as carpeting, vinyl tile, etc., a metal or
wood barrier covering the entire bottom surface
must be used.

5

12

X

Roof Pitch is X/12

2 FT
MIN.

2 FT MIN.

Lowest

Discharge

Opening

H*

*H = MINIMUM HEIGHT FROM ROOF TO

LOWEST DISCHARGE OPENING OF VENT

TERMINATION HEIGHTS FOR VENTS ABOVE

FLAT OR SLOPED ROOFS

Horizontal Overhang

Vertical
Wall

Vent

Termination

Storm Collar

Concentric

Vent Pipe

Flashing

1 inch (25.4 mm) Minimum
Clearance to Combustibles

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

VENT TERMINATION CLEARANCES

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) in the USA or
the current standards of CAN/CSA-B149.1
in Canada.

Vertical Vent Termination Clearances

Terminate multiple vent terminations according
to the installation codes listed above. Also see
Figure 4.

Terminate single vent caps relative to building
components according to Figure 5.

12”

(305mm)

Minimum

Vertical Vent Termination Clearances

Termination Heights For Vents

Above Flat Or Sloped Roofs
Ref. NFPA 54 / ANSI Z223.1

Roof Pitch * Feet * Meters

Flat to 6/12 1.0 0.3
6/12 to 7/12 1.25 0.38
7/12 to 8/12 1.5 0.46

8/12 to 9/12 2.0 0.61

9/12 to 10/12 2.5 0.76

10/12 to 11/12 3.25 0.99
11/12 to 12/12 4.0 1.22

12/12 to 14/12 5.0 1.52
14/12 to 16/12 6.0 1.83

The vent / air intake termination clearances
above the high side of an angled roof is as
shown in the following chart:

16/12 to 18/12 7.0 2.13

18/12 to 20/12 7.5 2.29
20/12 to 21/12 8.0 2.44

Figure 5

Horizontal Vent Termination Clearances

The horizontal vent termination must have a minimum of 6" (152 mm) clearance to any overhead
combustible projection of 2-1/2" (64 mm) or less (see Figure 6). For projections exceeding 2-1/2"
(64 mm), see Figure 6. For additional vent location restrictions refer to Figure 7 on Page 7.

Figure 4 - Multiple Terminations

6

Horizontal Vent Termination Clearances

Combustible Projection

inches or less in length

2-1/2

Combustible Projection greater

than 2-1/2 inches in length

Ventilated

Soffit

Unventilated

Soffit

6"

18"

(457 mm)

12"

(305 mm)

(152 mm)

Side Elevation View

Termination Kit

Figure 6

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

All horizontal terminations
may be located as close as
6” (152mm) to any
(non-combustible and
combustible) exterior
sidewall. This distance
may be decreased to 2”
(51mm) for non-­combustible exterior
sidewalls only, if the
SV4.5HT-2 termination
is used.

Termination Kit

Note - See Figure 30 on Page 19 for the exterior wall recess
allowances of the square horizontal termination.

NOTE: Local Codes Or Regulations

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LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

EXTERIOR HORIZONTAL VENT TERMINATION CLEARANCE REQUIREMENTS

* See Item D in the Text Below.

Exterior Wall

*18”

Horizontal
Termination

Inside Corner

B

V

L

V

6”

Detail D

F

V

A

Ventilated Soffit

V

Fixed

Closed

Window

V

C

X

= Air Supply Inlet

C

C

C

V

Inside

Corner Detail

V

A

B

Operable

V

Window

B

B

= Vent Termination

G

B

= Area where Termination is not Permitted

May Require Different Clearances.

NOTE: Location Of The Vent Termination
Must Not Interfere With Access To The
Electrical Service.

= 9” in U.S.



A

= 12” in Canada

3 ft.

X



A

3 ft.

J

Figure 7

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

P

N

Q

H



A

M

V

I

N

O

V

D

E

V

X

K

7

5 (127)

8-1/4

(209)

14

(356)

12 (305)

19

(483)

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

MINIMUM CLEARANCES TO COMBUSTIBLES

Appliance And Vent Clearances

The appliance is approved with zero clearance to combustible materials
on all sides (as detailed in Table 5), with the following exception: When

the unit is installed with one side flush with a wall, the wall on the
other side of the unit must not extend beyond the front edge of the
unit. In addition, when the unit is recessed, the side walls surrounding

the unit must not extend beyond the front edge of the unit (see Figure 3).

MINIMUM CLEARANCES* Inches (millimeters)

Back 0 (0) Spacers Or Dimples

Sides 0 (0) Spacers Or Dimples **

Top Spacers 0 (0) Spacers Or Dimples

Floor 0 (0)

From Bottom of Unit To Ceiling 64 (1626)

Vent 3 (76)

Top* / 1 (25.4) Sides & Bottom

SERVICE CLEARANCES Feet (meters)

Front 3 feet (0.9 meters)

Table 5

*Note: 3 in. (75 mm) above any horizontal/inclined vent component.

Model No.

MLDVT-30/35 *46-1/2 (1181) *48-1/4 (1226)
MLDVT-40/45 *51-1/2 (1308) *53-1/4 (1349)

Do not insulate the
space between the

appliance and the

area above it.

*Shelf Height

see table)

(

Figure 8 -

Shelf Height Minimum Clearances With Top Venting

Top Vent - with One 90 Degree Elbow

Secure Vent Secure Flex (flex elbow)

* Includes 3" clearance to
combustibles (required above
vent components)

Mantel Depth

Combustible Shelf Height - Inches (millimeters)

18 (457)

inches (millimeters)

16 (406)

**Note: See Step 1 on Page 9 for clearance requirements to the nail­ing flanges on each side of the unit and any adjacent screw heads.

Hearth Extension - A hearth extension is not required with this appliance.

If a hearth extension is used, do not block the lower control compartment
door. Any hearth extension used is for appearance only and does not
have to conform to standard hearth extension installation requirements.

Shelf Height - To provide for the lowest possible shelf surface, the venting

attached to the top vent should be routed in a way to minimize obstructions
to the space above the appliance. Do not insulate the space between the
appliance and the area above it (see Figure 8). The minimum height from
the base of the appliance to the underside of combustible materials used
to construct a utility shelf in this fashion is shown in Figure 8.

Wall Finishes / Surrounds / Mantels

Note: Combustible wall finish materials and/or surround materials must
not be allowed to encroach the area defined by the appliance front face
(black sheet metal). Never allow combustible materials to be positioned

in front of or overlapping the appliance face (see Figure 53 on Page 33).

Non-combustible materials, such as surrounds and other appliance trim,
may be installed on the appliance face with these exceptions: they must
not cover any portion of the removable glass panel.

Vertical installation clearances to combustible mantels vary according
to the depth of the mantel. See Figure 9. Mantels constructed of non-
combustible materials may be installed at any height above the appliance
opening; however, do not allow anything to hang below the fireplace hood.

NOTE: Use high-temperature paint (rated 175° F or higher) on the underside of
the mantel.

8

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

14 (356)

12 (305)

Header

Top of

10 (254)

8 (203)

Appliance

Note - Hood shown

12

(305)

10

(254)

(203)

6

8

(152)

(102)

2

4

(51)

as positioned.

Figure 9 - Minimum Mantel Clearances

At 14" minimum
side wall clearance,
a combustible wall
can project to any
length.

At 8-1/4" side
wall clearance, a
combustible wall
can project 12"

o

45

Protected wall shown in white

Top View of

Fireplace

Combustible Materials
Allowed In Shaded Area
“Safe Zone”

Combustible Walls
shown in dark gray

Combustible materials may
project beyond one side
of the fireplace opening
as long as they are kept
within the shaded areas
illustrated here.

Inches (millimeters)

Figure 10 - Minimum Distance to Unprotected Side Wall

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

WARNING

Failure to position the parts in
accordance with these diagrams
or failure to use only parts specifi­cally approved with this appliance
may result in property damage or
personal injury.

AVERTISSEMENT

Risque de dommages ou de
blessures si les pièces ne sont
pas installées conformément à
ces schémas et ou si des pièces
autres que celles spécifiquement
approuvées avec cet appareil sont
utilisées.

PRE-INSTALLATION STEPS

The appliance is shipped with all gas controls
and components installed and pre-wired.

1. Remove the shipping carton. Remove the
shipping pad, exposing the front glass door.

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 page numbers references in the follow­ing steps for detailed procedures.

Step 1. (Page 9) Construct the appliance

framing. Position the appliance within
the framing and secure with nailing
brackets.

Bend up the appropriate header spac-

ing guides for the drywall/finish mate­rial thickness to be used (see Figure

49). Bend up the outer pair for 1/2"
materials and the inner pair for 5/8"

materials.

Bend out the appropriate nailing

flanges for the drywall/finish material
to be used. Nailing flanges are provided
for flush framing, 1/2-inch, and 5/8­inch framing depths (see Figure 12).

Step 2. (Page 11) Route gas supply line to

appliance location.

Step 3. (Page 12) Install the vent system and

exterior termination.

DETAILED INSTALLATION STEPS
Step 1. FRAMING

Frame these appliances as illustrated in Figures
13 and 14 on Pages 10 and 11. (Figure 14

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 floor level,
a solid continuous platform must be constructed
below the appliance.

Headers may be in direct contact with the appli­ance top spacers when they are bent up vertically

maintaining the 3" clearance to the replace top,

but must not be supported by them or notched
to fit around them. All construction above the
appliance must be self-supporting. DO NOT use
the appliance for structural support.

The fireplace should be secured to the side
framing members using the unit’s nailing
flanges — one top and bottom on each side
of the fireplace front (see Figure 12). Use 8d
nails or their equivalent.

Unit
Nailing Flange

2. Open the two latches (located under the
rebox oor) securing the glass door. Re­move the door by tilting it outward at the
bottom and lifting it up. Set the door aside
protecting it from inadvertent damage. See
Removing Glass Panels on Page 31.

Step 4. (Page 24) Field Wiring
a. Millivolt Appliances – Install the

operating control switch (not fac-

tory provided) and bring in electrical

service line for forced air-circulating

blower (optional equipment).

b. Electronic Appliances – Field wire

and install operating control switch.

Step 5. (Page 25) Install blower kit (optional

equipment).

Step 6. (Page 26) Make connection to gas

supply.

Step 7. (Page 27) Verify appliance operation.
Step 8. (Page 28) Install the logs, decorative

volcanic stone and glowing embers.

Step 9. (Page 31) Install glass door assembly.
Step 10. (Page 31) Adjust burner primary air

shutter to achieve proper flame ap­pearance.

Step 11. (Page 33) Install the hood.
Step 12. (Page 34) Attach Safety-in-Operation

Warnings.

Side

Framing

Unit Being Secured by its Nailing

Flanges to the Framing

Left Side Front Corner of Fireplace Shown

(Right side requirements are the same.)

NOTE: The nailing flanges, combustible mem­bers and screw heads located in areas directly
adjacent to the nailing flanges, are EXEMPT from
the 1/2” clearance to combustible requirements
for the firebox outer wrapper.

Combustible framing may be in direct contact
with the nailing flanges and may be located
closer than 1/2” from screw heads and the
firebox wrapper in areas adjacent to the nailing
flanges.

Frame the opening to the exact dimensions
specified in the framing details of this manual.

Nailing Flanges Are
Provided At All Four
Corners At 5/8”, 1/2”
And Flush Settings

Figure 12 - Nailing Flanges

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

9

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

FIREPLACE AND FRAMING SPECIFICATIONS

Framing

Framing Dimensions

Model No. A B C D

MLDVT-30

MLDVT-35

MLDVT-40

MLDVT-45

MLDVT-30 57 55.6 58 56.1
MLDVT-35 57.5 55.6 59.0 58.1
MLDVT-40 62 61 62.3 59.5
MLDVT-45 63 60 64 62

Coaxial DV

Vent Size

Diagrams, illustrations and photo­graphs are not to scale – consult
install ation instructions. Product
design s, mat erials, dim ension s,
specifications, colors and prices are
subject to change or discontinuance
without notice.

in. 30-1/4 35-1/4 39-1/4 16

mm 768 895 997 406

in. 35-1/4 35-1/4 39-1/4 16

mm 895 895 997 406

in. 40-1/4 40-1/4 44-1/4 16

mm 1022 1022 1124 406

in. 45-1/4 40-1/4 44-1/4 16

mm 1149 1022 1124 406

Efficiencies (%)

Model

Natural Gas Propane

AFUE EnerGuide (P4) AFUE EnerGuide (P4)

Vent Size

4-1/2" Inner

7-1/2" Outer

Notes

Input (BTU/HR) - MV & Electronic

Natural & Propane Gas

Models Input Rate (BTU / HR)

MLDVT-30N 13,500
MLDVT-30P 12,500
MLDVT-35N 16,000
MLDVT-35P 15,000
MLDVT-40N 20,000
MLDVT-40P 20,000
MLDVT-45N 23,000
MLDVT-45P 22,000

K

1/2
(13)

L

*CONCENTRIC FLUE

FLUE - 4-1/2 (114)
COMBUSTION AIR

- 7-1/2 (190)

9-1/4 (235)

Top View

Framing should be

Vent Framing - Top Vent
With One 90° Elbow

B

10-1/2

(

5-1/8
(130)

C

constructed of 2x4 or
larger lumber.

)

267

7

(178)

12-1/8

(308)

D

1/2

A

A

Inches (millimeters)

Dimension D is the required framing depth when the
finish material (drywall) thickness is 1/2 in. (13mm)

Vertical Venting Through the Ceiling:
Frame ceiling opening - Use a plumb line from the ceiling above the appliance to

locate center of the vertical run. Cut and/or frame an opening, 10-1/2" x 10-1/2" (267
mm x 267 mm) inside dimensions, about this center mark (see Figure 18).

NOTE: It is recommended that the gas be stubbed in from the left
side only.

ELECTRICAL INLET
KNOCKOUT - 2-3/4 X 2

J

E

G

H

(70 X 51) COVER PLATE
(With KNOCKOUT ­Right Side Only)

GAS INLET

KNOCKOUT

(Other Side)

F

INLET KNOCKOUT,

REQUIRING A FIELD

JUNCTION BOX

OPTIONAL

ELECTRICAL

PROVIDED

(Either Side)

M

Front View

3 (76)

NOTE - Eyebrow
hood shown.

16 (406)

5-7/8
(149)

Right Side View

9-1/2
(241)

1-5/8

(42)

3 (76)

10

Figure 13

MLDVT-30

MLDVT-35

MLDVT-40

MLDVT-45

.oNledoM E F G H

32-1/4

28-1/8

.ni

819

mm

32-1/4

.ni

819

mm

37-1/4

.ni

946

mm

37-1/4

.ni

946

mm

23-1/4

715

587

686

28-1/8

23-1/4

58732813

715

28-1/4

33-1/8

71437940

841

33-1/8

28-1/4

841

714421067

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

27

J

30-1/4

76820508

35-1/4

89225635

40-1/4

101930762

45-1/4

114935889

K

L M

10

354

12-1/2

31733838

15

38138965

17-1/2

445

28

711

43

1092

Viewable Glass Size

30" Model

35" Model

40" Model

45" Model

24-1/4" Wide
20-1/4" High

29-1/4" Wide
20-1/4" High

34-1/4" Wide
25-1/4" High

39-1/4" Wide
25-1/4" High

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

FIREPLACE FRAMING SPECIFICATIONS

C

37 29/32

963

40 5/8

1032

43 11/32

1101

46 1/16

1170

26 13/16

28 3/4

30 11/16

32 5/8

MLDVT-30

MLDVT-35

MLDVT-40

MLDVT-45

.oNledoM A B D E

30 1/4

in.

mm

in.

mm

in.

mm

in.

mm

35 1/4

40 1/4

768

895

1022

45 1/4

1149

53 3/16

1350

57 1/2

1461

61 13/16

1554

66 1/8

1680

Figure 14 - Corner Framing with Horizontal Termination

Step 2. ROUTING GAS LINE

Never use galvanized or plastic pipe. Refer
to Table 6 for proper sizing of the gas sup-

Route a 1/2" (13 mm) gas line to the left side

of the appliance as shown in Figure 15. 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
6 on Page 26).

ply 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 qualified 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,

3"

(76 mm)

Left Side Front

Corner of Fireplace

Framing

Pipe Coupling

(Recommended)

6-1/2"

(152 mm)

pressure, sediment, and more. Certainly no one
unfamiliar and unqualified should attempt sizing
or installing gas piping.

Schedule 40 Pipe

Also see Figure 13.

Figure 15 - Route Gas Line

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).

Table 6

12 1/4

681

311

13 3/4

730

349

15 1/8

779

384

16 1/2

829

419

Back wall of chase/enclosure

(including any finishing materials)

Schedule 40

Black Iron Pipe

Inside Diameter (Inches)

Natural

Length (feet)

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

C

Propane

Gas

E

7 (178)

D

A

B

Inches

(millimeters)

Notes:

• All appliances are factory-equipped with a

flexible gas line connector and 1/2 inch shutoff
valve (see Figure 40 on Page 26).

• 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 6 (Page 26).

• 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. Appliances using propane should
have a sediment trap at the base of the tank.

• Check with local building ofcial 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.

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.

11

LENNOX HEARTH PRODUCTS • MERIT® SERIES DIRECT-VENT GAS FIREPLACES • MODELS MLDVT-30/35/40/45 • INSTALLATION INSTRUCTIONS

Step 3. INSTALL THE VENT SYSTEM

General Information

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) 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.

Dé gagement conforme a ux codes
d'installation locaux et aux exigences du
foumisseunde gaz.

Use only approved venting components.
See Approved Vent Components on

Page 2.

These fireplaces must be vented directly
to the outside.

The vent system may not service multiple
appliances, and must never be connected to a
flue serving a 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. The restrictor is installed in the
appliance top flue outlet as shown in Figure
16, either before adding vent, from above, or
after installation of vent from below, within the
firebox. The restrictor is self securing through
a positive friction fit.

Determine the venting for the appliance. If the

vent run will include at least 8 feet of vertical
rise, then install the restrictor in the appliance
collar before connecting any vent (Refer to

Figure 16). Place the restrictor inside the ap-
pliance vent collar and press in place.

Note: The restrictor is included within the
firebox.

Vent Restrictor Installation

(Top Vent)

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 all MLDVT series models. If needed,

install the restrictor orientated as shown,

either from inside or outside the unit,in the

Restrictor

Inner
Fireplace
Collar

inner fireplace collar.

Appliance Top

Vent Outlet

Figure 16

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 35 and 36.

12

NOTE: DIAGRAMS & ILLUSTRATIONS ARE NOT TO SCALE.