Monessen Hearth ACUF32-BD User manual

Installation Manual
Installation and Setup
INSTALLER: Leave this manual with party responsible for use and operation.
OWNER: Retain this manual for future reference.
VENT FREE FIREBOX
Model(s):
NOTICE: DO NOT discard this manual!
• DO NOT store or use gasoline or other
ammable vapors and liquids in the vicinity
of this or any other appliance.
• DO NOT overre. Overring will void your
warranty.
• Comply with all minimum clearances to
combustibles as specied. Failure to com-
ply may cause house re.
WARNING: If the information in these

or explosion may result causing property
damage, personal injury, or death.
Carefully review the instructions supplied
with the decorative type unvented room
heater for the minimum fireplace size
requirement.
DO NOT INSTALL AN APPLIANCE IN THIS
FIREBOX UNLESS THIS FIREBOX MEETS
THE MINIMUM DIMENSIONS REQUIRED
FOR THE INSTALLATION.
ACUF32-BD, ACUF32-GD
ACUF36-BD, ACUF36-GD
ACUF42-BD, ACUF42-GD
HOT SURFACES!
Firebox surfaces are hot during
operation AND cool down.
Hot surfaces will cause burns.
• DO NOT touch rebox until it is cooled
• NEVER allow children to touch rebox
• Keep children away
• CAREFULLY SUPERVISE children in same room as rebox.
• Alert children and adults to hazards of high temperatures.

materials.
• Keep clothing, furniture, draperies and other ammable
materials away.
DANGER
FOR USE ONLY WITH A LISTED GAS-FIRED UNVENTED DECO-
RATIVE ROOM HEATER NOT TO EXCEED 40,000 BTU/H.
DO NOT BUILD A WOOD FIRE.
1
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

Safety Alert Key:
• DANGER! Indicates a hazardous situation which, if not avoided will result in death or serious injury.
• WARNING! Indicates a hazardous situation which, if not avoided could result in death or serious injury.
• CAUTION! Indicates a hazardous situation which, if not avoided, could result in minor or moderate injury.
• NOTICE: Indicates practices which may cause damage to the replace or to property.
Table of Contents
Installation Standard Work Checklist 3
 
A. Firebox Certication 4
B. BTU Specications 4
C. High Altitude Installations 4
D. Non-Combustible Materials Specication 4
E. Combustible Materials Specication 4
F. Electrical Codes 4
2 Getting Started
A. Design and Installation Considerations 5
B. Tools and Supplies Needed 5
C. Inspect Firebox and Components 5
3Firebox Dimensions
A. Firebox Dimensions 6
B. Hearth Dimensions 7
C. Framing Dimensions 8
D. Clearance to Combustibles 9
E. Constructing the Appliance Chase 10
4 Firebox Preparation
A. Securing and Leveling the Firebox 11
B. Installing Optional Outside Air Kit(s) 11
5 Electrical Information
A. Wiring Requirements 12
B. Wiring the Junction Box 12
C. Electrical Service and Repair 12
D. Wiring Diagrams 13
6 Gas Information
A. Fuel Type 17
B. Gas Pressure 17
C. Gas Connection 17
7 Finishing
A. Facing Material 18
B. Mantel and Wall Projections 18
C. Decorative Fronts 19
D. TV Good Faith Guidelines 20
8 Firebox Setup
A. Remove the Shipping Materials 21
B. Clean the Firebox 21
C. Hood Installation 21
D. Adjustable Firebox Supports 21
9 Reference Materials
A. Optional Accessories 23
B. Contact Information 24
2Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

Customer:
Lot/Address
Model (circle one):
ACUF32-BD, ACUF32-GD
ACUF36-BD, ACUF36-GD
ACUF42-BD, ACUF42-GD
YES IF NO, WHY?
ATTENTION INSTALLER:
Follow this Standard Work Checklist
This standard work checklist is to be used by the installer in conjuction with, not instead of, the instructions contained in this installation
manual.
Date Installed:
Location of Firebox:
Installer:
Dealer/Distributor Phone #
Serial #:
WARNING! Risk of Fire or Explosion! Failure to install firebox acording to these instructions can lead to a fire or
explosion.
Comments communicated to party responsible
4136-982 • Rev A• 2/20
• Photographing the installation and copying this checklist for your file.
(Builder/Gen. Contractor) (Installer) (Date)
Comments: Further description of the issues, who is responsible (Installer/Builder/Other Trades, etc.) and corrective action needed:
• That this checklist remain visible at all times on the fireplace until the installation is complete.
__________________________ by ______________________on _________
Firebox Install Section(s) 3 & 4
Verified clearances to combustibles.
Firebox is leveled and secured.
Outside Air Kit Installed (Optional)
Electrical Section 5
Unswitched power (110-120 VAC) provided to the firebox.
Gas Section 6
Proper fuel type
Leak check performed and inlet pressure verified.
Finishing Section 7
Combustible materials not installed in non-combustible areas.
Verified all clearances meet installation manual requirements.
Mantels and wall projections comply with installation manual requirements.
Hearth extension installed per manual requirements.
Firebox Setup Section 8
All packaging and protective materials removed.
Refractory installed correctly.
Firescreen installed properly.
Manual bag and all of its contents are removed from the firebox and given to
the party responsible for use and operation.
Blower kit installed properly. (Optional)
Light kit installed properly. (Optional)
Hearth & Home Technologies recommends the following:
3
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

 
NOT INTENDED FOR USE AS A PRIMARY HEAT SOURCE.
This appliance is tested and approved as either supplemen-
tal room heat or as a decorative appliance. It should not be
factored as primary heat in residential heating calculations.
NOTICE: This installation must conform with local codes.
In the absence of local codes you must comply with the
National Fuel Gas Code, ANSI Z223.1/NFPA 54.
This product is listed to ANSI standards for “Ventless Gas
Firebox Enclosures for Gas-Fired Unvented Gas Log
Type Room Heaters".
MODELS: ACUF32-BD, ACUF32-GD
ACUF36-BD, ACUF36-GD
ACUF42-BD, ACUF42-GD
LABORATORY: Underwriters Laboratories, Inc. (UL)
TYPE: Ventless Firebox Enclosures for Gas-Fired
Unvented Gas Log Type Room Heaters
STANDARD: CSA/ANSI-Z21.91:20
 
WARNING: This product and the
fuels used to operate this product (liquid
propane or natural gas), and the products
of combustion of such fuels, can expose
you to chemicals including benzene, which
is known to the State of California to cause
cancer and reproductive harm. For more
information go to: www.P65Warnings.
ca.gov.
This product is for use ONLY with a listed decorative
"Gas-Fired Unvented Room Heaters".
1  
Model(s) Altitude Maximum
Allowable
BTU/hr
ACUF32-BD/GD (0-2000 FT) 30,000
ACUF36-BD/GD (0-2000 FT) 40,000
ACUF42-BD/GD (0-2000 FT) 40,000
 
Material which will not ignite and burn. Such materials are
those consisting entirely of steel, iron, brick, tile, concrete,
slate, glass or plasters, or any combination thereof.
Materials that are reported as passing ASTM E 136,
Standard Test Method for Behavior of Materials in
a Vertical Tube Furnace at 750 ºC shall be considered
non-combustible materials.
 
Materials made of or surfaced with wood, compressed pa-
per, plant bers, plastics, or other material that can ignite
and burn, whether ame proofed or not, or plastered or
unplastered shall be considered combustible materials.
F. Electrical Codes
NOTICE: This appliance must be electrically wired
and grounded in accordance with local codes or, in the
absence of local codes, with National Electric Code
ANSI/NFPA 70-latest edition.
C. High Altitude Installations
NOTICE: If the heating value of the gas has been reduced,
these rules do not apply. Check with your local gas utility
or authorities having jurisdiction.
When installing above 2000 feet elevation:
• In the USA: Reduce input rate 4% for each 1000 feet
above 2000 feet.
Check with your local gas utility to determine proper
orice size.
Note: Smoke, carbon monoxide or combination alarms
Alarm manufacturers recommend that alarms be kept at
least 15 ft. to 20 ft. laterally away from fuel-burning sources.
Installing the alarm closer than 15 ft. will not harm the
alarm, but may increase the frequency of nuisance alarms.
Mounting alarms on the wall versus the ceiling will further
reduce nuisance alarms.
4Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

A. Design and Installation Considerations
Installation MUST comply with local, regional, state and
national codes and regulations. Consult insurance carrier,
local building inspector, re o󰀩cials or authorities having
jurisdiction over restrictions, installation inspection and
permits.
Before installing, determine the following:
• Where the rebox is to be installed.
• Gas supply piping requirements.
• Electrical wiring requirements.
• Framing and nishing details.
• Whether optional accessories - are desired.
C. Inspect Firebox and Components
• Carefully remove the rebox and components from the
packaging.
• Report to your dealer any parts damaged in shipment.
•Read all of the instructions before starting the instal-
lation. Follow these instructions carefully during the

WARNING! Risk of Fire or Explosion! Damaged parts
could impair safe operation. DO NOT install damaged,
incomplete or substitute components. Keep rebox dry.
B. Tools and Supplies Needed
Before beginning the installation be sure that the following
tools and building supplies are available.
Tape measure Framing material
Pliers Hammer
Phillips screwdriver Level
Gloves Framing square
Electric drill and bits
Safety glasses
Reciprocating saw
Caulking material (300ºF minimum continuous exposure
rating)
Note: Refer to the installation instructions provided with
the log set for items required for log set installation.
Hearth & Home Technologies disclaims any responsibility
for, and the warranty will be voided by, the following actions:
• Installation and use of any damaged rebox or system
component.
• Modication of the rebox.
• Installation other than as instructed by Hearth & Home
Technologies.
• Improper positioning of the gas logs.
• Installation and/or use of any component part not approved
by Hearth & Home Technologies.

WARNING! Risk of Fire, Explosion or Electric Shock!
DO NOT use this rebox if any part has been under water.
Call a qualied service technician to inspect the rebox
and to replace any part of the control system and/or gas
control which has been under water.
Improper installation, adjustment, alteration, service or
maintenance can cause injury or property damage. For
assistance or additional information, consult a qualied
service technician, service agency or your dealer.
Installation and service of this appliance should be performed by
qualied personnel. Hearth & Home Technologies recommends
HHT Factory Trained or NFI certied professionals.
2 Getting Started
5
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

3 Firebox, Hearth, Framing Dimensions and Clearances
A. Firebox Dimensions
Dimensions are actual rebox dimensions. Use for reference only. For framing dimensions and clearances refer to page 8.
Figure 3.1 Firebox Dimensions
B
4 in
(102 mm)
27 in
(686 mm)
3 in
(76 mm)
34 in
(864 mm)
A
20 in
(508 mm)
15-7/8 in
(403 mm)
5-3/4 in
(146 mm)
5-3/4 in
(146 mm)
15-7/8 in
(403 mm)
2 in
(51 mm)
7-3/4 in
(197 mm)
2 in
(50 mm) 9-3/8 in
(238 mm)
32" 36" 42"
A 32 in (813 mm) 36 in (914 mm) 42 in (1067 mm)
B 38 in (965 mm) 42 in (1067 mm) 48 in (1219 mm)
Gas Access
Above Hearth
Outside Air
Electrical Access
Wall Switch
Strain Relief
Outside
Air Gas Access
Above Hearth
Gas Access
Below Hearth
6Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

A
B
C
DE
FP2901
hearth dims
Figure 3.2 Minimum Hearth Dimensions
Model A B C D E
ACUF32 28-7/8 in. 15 in. 20-3/8 in 25-1/2 in. 22-5/8 in.
ACUF36 32-7/8 in. 15 in. 24-3/8 in. 25-1/2 in. 22-5/8 in.
ACUF42 38-7/8 in. 15 in. 30-3/8 in. 25-1/2 in. 22-5/8 in.
B. Hearth Dimensions
.
7
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

C. Framing Dimensions
WARNING! Risk of Fire or Burns! Provide adequate
clearance around air openings and for service access.
Due to high temperatures, the appliance should be lo-
cated out of trac and away from furniture and draperies.
NOTICE: Illustrations reect typical installations and are
FOR DESIGN PURPOSES ONLY. Illustrations/diagrams
are not drawn to scale. Actual installation may vary due to
individual design preference.
Figure 3.3 Framing Dimensions
A
5/8 in
B
F
E
D
D
5/8 in C
MODEL A B C D E F
ACUF32 38-1/2 in 34-1/4 in 19-3/4 in 47-1/4 in 66-3/4 in 33-1/2 in
ACUF36 42-1/2 in 50 in 70-3/4 in 36 in
ACUF42 48-1/2 in 54-1/4 in 76-3/4 in 38-1/2 in
Note: Add 1/2 inch to width (A) and 1/4 inch to
height (B) dimensions when using optional trim
kit to nish the installation of a custom cabinet,
mantle, or other built-in enclosure.
34-1/4 in
34-1/4 in
19-3/4 in
19-3/4 in
8Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

D. Clearances to Combustibles
Carefully select the best location for installation of your
vent-free rebox. The following factors should be taken
into consideration:
• Clearance to side walls and ceiling. Minimum clearances
to combustibles must be maintained.
• Location must not be a󰀨ected by drafts caused by
kitchen exhaust fans, ceiling fans, return air registers for
forced air furnaces / air conditioners, windows or doors.
• Installation must provide adequate ventilation and com-
bustion air.
Figure 3.4 Clearances to Combustibles
• Location should be out of high tra󰀩c or windy or drafty
areas.
• DO NOT INSTALL WHERE CURTAINS, FURNITURE,
CLOTHING OR OTHER FLAMMABLE OBJECTS ARE
LESS THAN 36" FROM FRONT OF FIREBOX.
• Never obstruct the front opening of the vent-free rebox
or restrict the ow of combustion and ventilation air.
0" in to back
0" in to side
0 in
Drywall
Combustible flooring may be installed next to the front of the appliance.
(No carpet or vinyl within 14 inches)
6 in. (152 mm) min.
9 in (229 mm) min.
(from firebox opening)
Drywall
Perpendicular
Wall
36 in
(914 mm)
Combustible Object
42 in to ceiling
(1067 mm)
0 in to floor
0 in to standoffs
9
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

Raised Hearth Extension
A hearth extension may be used, but is not required for
these reboxes.
A combustible hearth extension can be constructed ush
with, but not above the rebox oor. On ush installa-
tions, carpet or vinyl is not allowed within 14 inches of
the rebox opening. See Figure 3.5.
Figure 3.5 Raised Hearth Extension
Firebox framing can be built before or after the appliance is
set in place. Construct rebox framing following Figure 3.3
for your specic installation requirements. Refer to Figure
3.1 on page 6 for rebox dimensions.
The rebox may be installed directly on a combustible
oor or raised on a platform. When the rebox is installed
directly on carpeting, tile, or other combustible material,
other than wood ooring, the rebox shall be installed on a
metal or wood panel extending the full width and depth of
the enclosure.
WARNING! Risk of Fire! DO NOT ll spaces around re-
box with insulation or other materials. This could cause a
re.
WARNING! Risk of Fire! The rebox must be installed
giving full consideration to the clearance and height re-
quirements identied in this manual.
E. Constructing the Appliance Chase
A chase is a vertical box-like structure built to enclose the
rebox.
NOTICE: These instructions are not substitutes for the
requirements of local building codes. Therefore, you MUST
check local building codes to determine the requirements
to these steps.
Chases should be constructed in the manner of all outside
walls of the home to prevent cold air drafting problems. The
chase should not break the outside building envelope in
any manner.
Walls, ceiling, base plate and cantilever oor of the chase
should be insulated. Vapor and air inltration barriers should
be installed in the chase as per regional codes for the rest
of the home. Additionally, in regions where cold air inltra-
tion may be an issue, the inside surfaces may be sheet
rocked and taped (or an equivalent method may be used)
to achieve maximum air tightness.
To further prevent drafts, gas line holes and other open-
ings should be caulked with caulk with a minimum of 300ºF
continuous exposure rating or stu󰀨ed with unfaced insulation.
If the rebox is being installed on a cement surface, a layer of
plywood may be placed underneath to prevent conducting cold
up into the room.
NOTICE: Install rebox on hard metal or wood surfaces
extending full width and depth. DO NOT install directly on
carpeting, vinyl, tile or any combustible material other than
wood.
WARNING! Risk of Fire! Maintain specied air space
clearances to rebox:
• Insulation and other materials must be secured to prevent
accidental contact.
• The chase must be properly blocked to prevent blown
insulation or other combustibles from entering and making
contact with rebox.
• Failure to maintain airspace may cause overheating and
a re.
0" Minimum
Combustible Platform
Raised Hearth Extension
(Combustibles allowed;
No carpet or vinyl within
14 inches)
Firebox Floor
10 Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

A. Securing and Leveling the Firebox
WARNING! Risk of Fire! Prevent contact with:
• Sagging or loose insulation
• Insulation backing or plastic
• Framing and other combustible materials
Block openings into the chase to prevent entry of blown-
in insulation. Make sure insulation and other materials
are secured.
DO NOT notch the framing around the rebox standos.
Failure to maintain air space clearance could cause
overheating and re.
The diagram shows how to properly position and secure the
rebox. See Figure 4.1. Nailing tabs are provided to secure
the rebox to the framing members.
• Bend out nailing tabs on each side.
• Place the rebox into position.
• Keep nailing tabs ush with the framing.
• Level the rebox from side to side and front to back.
• Shim the rebox as necessary. It is acceptable to use
wood shims underneath the rebox.
• Secure the rebox to the framing by using nails or screws
through the nailing tabs.
Figure 4.1 Proper Positioning and Securing
of Firebox
B. Installing Optional Outside Air Kit(s)
Figure 4.2 Optional Outside Air Kit(s)
4 Firebox Preparation
Note: The outside air kit is an optional accessory that
can be used to bring in fresh air. Use of the air kit is not
required for operation unless specied by local codes.
CAUTION! Risk of cuts/abrasions/ying debris. Wear
protective gloves and safety glasses during installation.
Sheet metal edges are sharp.
WARNING! Risk of re/asphyxiation. DO NOT draw
outside combustion air from:
• Wall, oor or ceiling cavity.
• Enclosed space such as an attic or garage.
• Close proximity to exhaust vents or chimneys. Fumes
or odor may result.
Note: The outside air kit(s) can be installed on the left
and/or right side of the rebox.
Refer to the Installation Instructions provided with the Out-
side Air Kit for specic step by step instructions.
WARNING! Risk of Fire! DO NOT remove the cover on
side of rebox if the outside air will not be connected.
Nailing Tabs
(both sides)
Outside Air Hood
Wire Ties
Flexible Duct
(not supplied)
Outside Air Collar
Outside Air Door
11
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

A. Wiring Requirements
WARNING! Risk of Shock or Explosion! DO NOT wire
110-120 VAC to the valve. Incorrect wiring will damage
controls.
NOTICE: This firebox must be electrically wired and
grounded in accordance with local codes or, in the absence
of local codes, with National Electric Code ANSI/NFPA
70-latest edition.
• Wire the rebox junction box to unswitched 110-120 VAC.
This is required for proper operation of the rebox ignition.
• A 110-120 VAC circuit for this product must be protected
with ground-fault circuit-interrupter protection, in
compliance with the applicable electrical codes, when it is
installed in locations such as in bathrooms or near sinks.
• Low voltage and 110-120 VAC voltage cannot be shared
within the same wall box.
5 Electrical Information
B. Wiring the Junction Box
Junction box wiring on this rebox can be done from ei-
ther inside or outside of the rebox. However, for ease of
installation, it is recommended that the junction box be
wired from outside of the rebox.
If the junction box is wired from OUTSIDE rebox:
• Remove the screw attaching the junction box cover to the
outer shell. Pull junction box cover out to disengage it
from the outer shell. See Figures 5.1.
Figure 5.1 Junction Box Cover Removal
• Install electrical wires from outside the appliance
through the hole in the cover plate and secure wires
with a Romex connector.
• Make all necessary wire connections to the junction
box and reattach the cover plate to rebox outer shell.
See Figure 5.2.
C. Electrical Service and Repair
WARNING! Risk of Shock! Label all wires prior to dis-
connection when servicing controls. Wiring errors could
cause improper and dangerous operation. Verify proper
operation after servicing.
WARNING! Risk of Shock! Replace damaged wire with
type 105º C rated wire. Wire must have high temperature
insulation.
Figure 5.2 Reattaching Junction Box Cover
12 Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

D. Wiring Diagrams
Figure 5.4 Wiring Diagram - Standard
BLOWER
TEMPERATURE
SENSOR
FAN CONTROL
MOUNTED IN FIREBOX
F
FF
F
JUNCTION BOX
WIRE HARNESS
M M
F F
F F
M M
WIRE HARNESS
M F
LIGHT SOCKET
ASSEMBLY
F F
POWER CORD
LIGHT CONTROL
MOUNTED IN FIREBOX
BLK
GRN
WHT
13
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

14-2 MINIMUM
BLK
WHT
WHT
BLK
FAN CONTROL
MOUNTED IN REMOTE
WALL BOX
BLOWER
TEMPERATURE
SENSOR
F
F
JUNCTION BOX
WIRE HARNESS
M M
F F
F F
M M
WIRE HARNESS
F F
POWER CORD
LIGHT CONTROL
MOUNTED IN FIREBOX
BLK
GRN
WHT
M F
LIGHT SOCKET
ASSEMBLY
KNOCKOUT
Note: Wires supplied from
remote wall box loca�ons, to
pass through provided knockout
in face of junc�on box.
Figure 5.5 Wiring Diagram - Remote Fan Control
14 Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

BLOWER
TEMPERATURE
SENSOR
FAN CONTROL
MOUNTED IN
FIREBOX
F
F
JUNCTION BOX
WIRE HARNESS
M M
F F
F F
POWER CORD
BLK
GRN
WHT
14-2 MINIMUM
WHT
BLK
BLK
WHT
LIGHT CONTROL
MOUNTED IN REMOTE
WALL BOX
M F
LIGHT SOCKET
ASSEMBLY
Note: Wires supplied from
remote wall box loca�ons, to
pass through provided knockout
in face of junc�on box.
KNOCKOUT
Figure 5.6 Wiring Diagram - Remote Light Control
15
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

14-3 MINIMUM
FAN CONTROL
BLK
WHT
RED
RED WHT
BLK
BOTH FAN AND LIGHT CONTROLS
MOUNTED IN REMOTE WALL BOX
LIGHT CONTROL
BLOWER
TEMPERATURE
SENSOR
JUNCTION BOX
WIRE HARNESS
M M
F F
M F
LIGHT SOCKET
ASSEMBLY
F F
POWER CORD
BLK
GRN
WHT
Note: Wires supplied from
remote wall box loca�ons, to
pass through provided knockout
in face of junc�on box.
KNOCKOUT
Figure 5.7 Wiring Diagram - Remote Fan and Light Controls
16 Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

A. Fuel Type
Check gas type: The gas supply must be the same as
stated on the appliance rating plate. If the gas supply is
di󰀨erent, DO NOT INSTALL THE APPLIANCE. Contact
your dealer for the correct model.
B. Gas Pressure
• Optimum appliance performance requires proper input
pressures.
• Gas line sizing requirements will be determined in ANSI
Z223.1 National Fuel Gas Code in the USA.
• Pressure requirements are:
C. Gas Connection
• Reference Section 3 for location of gas line access in
appliance.
• The gas line may enter from the left side or right side of
the rebox. Gas knockouts are provided on both side of
the rebox, as well as on the rebox bottom. See Figure
6.1.
WARNING! Risk of Fire or Explosion! High pressure
will damage valve. Low pressure could cause explosion.
• Verify inlet pressures. Verify minimum pressures when
other household gas appliances are operating.
• Install regulator upstream of valve if line pressure is
greater than 1/2 psig.
Gas Pressure Natural Gas Propane
Minimum inlet pressure 5.0 in. w.c. 11.0 in. w.c.
Maximum inlet pressure 10.0 in. w.c. 13.0 in. w.c.
Note: Have the gas supply line installed in accordance with
local codes, if any. If not, follow ANSI Z223.1. Installation
should be done by a qualied installer approved and/or
licensed as required by the locality. (In the Commonwealth
of Massachusetts installation must be performed by a
licensed plumber or gas tter).
Note: A listed (and Commonwealth of Massachusetts ap-
proved) 1/2 in. (13 mm) T-handle manual shut-o󰀨 valve
must be installed upstream of the appliance. A union tee
and plugged 1/8" NPT pressure tapping point should also
be installed upstream of the appliance.
IMPORTANT: Install manual shut-o󰀨 valve (equipment
shuto󰀨 valve) in an accessible location. The manual
shut-o󰀨 valve is for turning on or shutting o󰀨 the gas to
the rebox.
Fire Risk.
Explosion Hazard.
High pressure will damage valve.
• Disconnect gas supply piping BEFORE
pressure testing gas line at test pressures
above 1/2 psig.
• Close the manual shuto󰀨 valve BEFORE
pressure testing gas line at test pressures
equal to or less than 1/2 psig.
WARNING
6 Gas Information
• The gap between supply piping and gas access hole may
be caulked with caulk with a minimum of 300ºF continuous
exposure rating or stu󰀨ed with non-combustible, unfaced
insulation to prevent cold air inltration.
• Ensure that gas line does not come in contact with outer
wrap of the rebox. Follow local codes.
• Pipe incoming gas line into rebox.
• Refer to vent-free gas appliance installation instructions
for gas connection and lighting instructions.
WARNING! Risk of Fire or Explosion! Support control
when attaching pipe to prevent bending gas line.
• A small amount of air will be in the gas supply lines.
WARNING! Risk of Fire or Explosion! Gas build-up
during line purge could ignite.
• Purge should be performed by qualified service
technician.
• Ensure adequate ventilation.
• Ensure there are no ignition sources such as sparks or
open ames.
Light the appliance. It will take a short time for air to purge
from lines. When purging is complete the appliance will
light and operate normally.
WARNING! Risk of Fire, Explosion or Asphyxiation!
Check all ttings and connections with a non-corrosive
commercially available leak-check solution. DO NOT use
open ame. Fittings and connections could have loosened
during shipping and handling.
Figure 6.1
Gas Access
Holes, Side
Gas Access Holes, Hearth
17
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

7 Finishing
A. Facing Material
WARNING! Risk of Fire! Metal front faces may be cov-
ered with non-combustible materials only.
• Facing and/or nishing materials must not interfere with
air ow through the front of the rebox.
• Facing and/or nishing materials must never overhang
into the rebox opening.
• See Figures 7.1, 7.2 and 7.3 for combustible and non-
combustible nishing material thickness and clearance
requirements.
• Maintain all listed clearances when applying combustible
materials.
• Seal joints between the nished wall and rebox top and
sides using a 300º F minimum sealant.
WARNING! Risk of Fire! DO NOT apply combustible ma-
terials beyond the minimum clearances. Comply with all
minimum clearances to combustibles as specied in this
manual. Overlapping materials could ignite and may inter-
fere with proper operation.
NOTICE: Surface temperatures around the rebox will
become warm while the rebox is in operation. Ensure
nishing materials used for all surfaces (oor, walls, mantels,
etc.) will withstand temperatures up to 190°F.
B. Mantel and Wall Projections
WARNING! Risk of Fire! Comply with all minimum clear-
ances as specied.
Combustible/Noncombustible Mantels
Figure 7.1 Minimum Vertical and Maximum Horizontal Dimensions of Combustible and Noncombustible
Note: Mantel Measurement is taken from top of
the rebox opening, NOT the top of the unit.
• Reducing non-combustible mantel and/or mantel leg
clearances closer than those listed in this manual
requires the use of non-combustible construction
materials (eg: steel studs, concrete boards, etc.) to a
minimum height of 12 inches (305 mm) above the listed
framing height.
1"
2"
3"
4"
5"
6"
7"
8"
9"
10"
11"
12"
13"
14"
15"
16"
17"
18"
1"
2"
3"
4"
5"
6"
7"
8"
9"
10"
11"
12"
13"
14"
15"
16"
17"
18"
18 in. Maximum
Gray area is
combustible
material
6 in.
Minimum
3 in. Minimum
17 in.
White area is
non-combustible
material
17 in.
Measured from top of appliance opening
Seal joint with
non-combustible
sealant to
prevent heat
from being
drawn into the
wall cavity.
Note: Reducing clearances further requires non-combustible construction materials (eg: steel studs, durock, etc) to a height of 12 inches above the framing height.
18 Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

Figure 7.2 Combustible & Non-Combustible Mantel
Leg or Wall Projections
Combustible or Non-Combustible Mantel Legs or
Wall Projections
 
Only decorative fronts certied for use with this rebox
model may be used. Contact your dealer for a list of deco-
rative fronts that may be used.
Minimum Side Wall
Unit Gray area is
combustible
material
White area is
non-combustible
material only
1"
2"
3"
4"
5"
6"
7"
8"
9"
1"
2"
3"
4"
5"
6"
9.00”
6.00”
9.00”
19
Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21

Figure 7.3 Good Faith Clearances
D. TV Good Faith Guidelines.
Combus�ble Mantel
A
inch
17.00
mm
432
Non-Combus�ble Mantel
inch
12.00
mm
305
Good Faith Guidelines for TV Installa�on’s above a Typical Gas Fireplace
TV on the wall TV recessed into the wall
Notes:
1. These are good faith recommended clearances only and not a guarantee of compliance with all TV
manufacturers’maximum allowable operating temperatures.
2. Since every home has unique air ow characteristics and maximum allowable operating temperatures
can vary from manufacturer to manufacturer and from model to model, actual TV temperatures should be
validated at the time of each installation. TVs should not be used in situations where the actual TV
temperature exceeds the manufacturers’maximum allowable operating temperatures identied in the
TV’s technical specications. Contact the TV’s manufacturer directly if you cannot locate this information
or have questions regarding the information.
3. Mantel height and depth must conform to mantel requirements specied in the replace installation
manual.
4. “A”dimension taken from the top of the rebox opening.
5. Suggestions on how to further reduce TV temperatures:
-Increase “A” and/or 24” minimum TV height dimensions.
6" Min.
A Min.
24" Min.
12" Min.
TV
24" Min.
A Min.
12" Min.
TV
20 Monessen • ACUF32/36/42 Installation Manual • 4136-901 • Rev A • 01/21