Literature number 32472
hydro flame™
AFL Series Furnaces Models
AFLD35, AFLD40
AFLA35, AFLA40
Atwood Mobile Products
1120 North Main Street • Elkhart, IN 46514
USA & Canada : 1-866-869-3118
Internet: http://www.atwoodmobile.com

Technical Installation Manual
Effective 8/15

English, Français (et Canada)
This instruction manual is for use by an authorized service technician
to install an Atwood – hydro flame™ furnace. Should you require
further information, contact your dealer or Atwood Mobile Products
LLC.
This furnace design has been certified for installation in recreation
vehicles as a MSP Category III furnace. Follow this installation
instruction to insure safe operation of the furnace. Failure to install
furnace according to this installation instruction nullifies the furnace
warranty.

WARNING
Installation of this appliance must be made in accordance with the
written instructions provided in this manual. No agent, representative
or employee of Atwood or other person has the authority to change,
modify or waive and provision of the instructions contained in this
manual.

WARNING
TO THE INSTALLER: LEAVE THIS MANUAL WITH THE
APPLIANCE.
TO THE CONSUMER: RETAIN THIS MANUAL FOR FUTURE
REFERENCE.

SAFETY ALERT SYMBOLS

Avoid possible injury or death
Improper installation, adjustment, alteration, service or maintenance
can cause property damage, personal injury or loss of life. Refer to the
installation instructions and/or owner’s manual provided with this
appliance. A qualified installer, service agency or the gas supplier must
perform installation and service.

Safety Symbols alerting you to potential personal safety
hazards obey all safety messages following these symbols

FOR YOUR SAFETY
WARNING
Avoid possible injury or
death

CAUTION
Avoid possible injury
and/or property damage

Do not store or use gasoline or other flammable vapors and liquids in
the vicinity of this or any other appliance.

WARNING
WARNING
FIRE OR EXPLOSION

Be sure the furnace and all ignition systems are “off” during any type of
refueling and while vehicle is in motion or being towed.

If the information in this manual is not followed exactly, a
fire or explosion may result causing property damage,
personal injury or loss of life.

FOR YOUR SAFETY
WHAT TO DO IF YOU SMELL GAS:
 Extinguish any open flame.
 Evacuate all persons from the vehicle.
 Shut off the gas supply at the gas container or
source.
 Do not touch any electrical switch, or use any
phone or radio in the vehicle.
 Do not start the vehicle’s engine or electric
generator.
 Contact the nearest gas supplier or qualified
service technician for repairs.
 If you cannot reach a gas supplier or qualified
service technician, contact the nearest fire
department.
 Do not turn on the gas supply until the gas
leak(s) has been repaired.
A qualified Service Technician
Service Center or gas supplier must perform
installation and service.

CRITICAL INSTALLATION WARNINGS
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DO NOT install furnace on material that restricts return air, like
carpet or any soft material such as vinyl.
DO NOT install furnace where clearance to combustibles cannot be
maintained.
DO NOT modify furnace or intake and exhaust vent in any way.
DO NOT alter furnace for a positive grounding system.
DO NOT hi pot furnace unless electronic ignition system (circuit
board) has been disconnected.
DO NOT use battery charger to supply power to DC model furnace
even when testing.
DO NOT use 120-volt AC current with DC models.
DO NOT use furnace cabinet area as a storage compartment.
DO NOT vent furnace with venting system serving another
appliance.
DO NOT vent furnace to an outside enclosed porch area.
DO NOT use for temporary heating of buildings or structures under
construction.
Protect building materials from degrading from flue gas exhaust.
Protect furnace electrical components from water.
Compartment must be closed when operating unit.
Should the gas supply fail to shut off or if overheating occurs, shut
off the gas valve to the furnace before shutting off the electrical
supply.
DO NOT use this furnace if any part has been under water.
DO NOT use petroleum or citrus type cleaner on plastic parts, as
damage may occur.

AIR FLOW CHECK ....................................................................... 4

FURNACE INSTALLATION .................................................... 4

CAUTION
PERSONAL INJURY

SIDEWALL CUTOUT .................................................................... 4

WALL CUTOUT ....................................................................... 4

All sheet metal edges are sharp care should be taken when
handling or brushing up against them.

SMALL VENT INSTALLATION ..................................................... 5
FLUSH DOOR INSTALLATION .................................................... 5
HARD DUCTING SYSTEMS ......................................................... 5
HORIZONTAL FLOOR DISCHARGE CUTOUT ............................ 6
GAS CONNECTION ...................................................................... 6

WARNING
CARBON MONOXIDE POISONING

CONVERTIBLE GAS CONTROL ............................................ 6
VALVE CONVERSION .................................................................. 7
ORIFICE REPLACEMENT ............................................................ 7

Properly seal vent assembly to prevent carbon monoxide from entering
coach.
 DO NOT draw combustion air from living area.
 DO NOT vent exhaust air into the living area or an enclosed porch.

ELECTRICAL CONNECTIONS ............................................... 7
12 VOLT DC WIRING .................................................................... 7
120 VOLT AC WIRING .................................................................. 8

THERMOSTAT INSTALLATION ............................................. 8
OPERATING INSTRUCTIONS ................................................ 8
TO SHUT DOWN........................................................................... 9

WARNING

IGNITION CONTROL DIAGNOSTIC CODES ......................... 9

CARBON MONOXIDE POISONING
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Furnace must be installed and vented to these instructions.
Improper installation, adjustment, alteration, service or
maintenance can cause injury or property damage.
Improper installation location may cause furnace to produce negative
pressure, affecting combustion air or venting of other appliances.

MODEL SPECIFICATIONS
Models

WARNING
CARBON MONOXIDE POISONING
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Properly seal door to prevent carbon monoxide from entering
coach.
Properly adjust draft cap to prevent carbon monoxide from entering
coach.

M

D

25

1

1

1

A

Atwood
Furnace

Cabinet
Size

Voltage

Input
Btu/hr

Gas
Type

Style

Valve

Model
Rev

AF

L=large

D=12
VDC

35K

1=LP

1=door

A=120
VAC

40K

2=LP/NAT

2=LD (small
vent)

1=
Single

AFLD40

AFLD35

AFLD40

BTU Input

35,000

40,000

35,000

40,000

Duct Static
Pressure

.10” WC

.10” WC

.10” WC

.10” WC

Amperage
(AMPS)

12.5*

12.5*

2.5

2.5

Watts

138

138

154

154

12VDC

12VDC

120VAC

120VAC

Recommended
Return Air

80 in2

80 in2

80 in2

80 in2

Minimum Hard
Duct Return Air

65 in2

65 in2

65 in2

65 in2

Minimum
Discharge Air

48 in2

48 in2

48 in2

48 in2

Type of Gas

Propane
LP

Propane
LP

Propane
LP &
Natural
Gas

Propane
LP &
Natural
Gas

Power Supply

MODEL NOMENCLATURE
AF

AFLD35

A

3=door w/
rear gas
fitting

(WC = WATER COLUMN)
* 20 AMP DECATATED CIRCUIT TO THE FURNACE

4=door
w/pigtail

DIMENSIONS

5=door
w/pigtail
rear gas
fitting

All Models

Width

Height

Depth

Casing

16-1/2”

9”

20”

Door

19-1/4”

9-1/4”

1/4”

Recess Bezel

20-9/16”

11-1/2”

3/8”

5”

5-3/8”

1”

LD Vent

Contents

Weight
Furnace 39
lbs
Boxed 46
lbs

INSTALLATION AND SAFETY CODES
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USA and Canada – follow all applicable state and local codes in
the absence of local codes or regulations, refer to current
standards of:
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ANSI/NFPA 1192 Recreational Vehicles Code and ANSI/RVIA LV
Low Voltage Systems in Conversion and Recreational Vehicles
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CSA Z240.4, Gas-Equipped Recreational Vehicles and Mobile
Housing
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National Fuel Gas Code ANSI Z223.1 and/or CAN/CGA B149
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This furnace must be installed in accordance with the
manufacturer’s instructions and the manufactured Home
Construction and Safety Standard, Title 24 CFR, part 3280, or

MODEL NOMENCLATURE .....................................................2
MODEL SPECIFICATIONS .....................................................2
DIMENSIONS...........................................................................2
INSTALLATION AND SAFETY CODES....Error! Bookmark not
defined.
INSTALLATION CODES ................ Error! Bookmark not defined.

GENERAL FURNACE INSTALLATIONS ................................ 3
CLEARANCE TO COMBUSTIBLES ............................................. 3
REQUIRED DUCTING ................................................................... 3
REQUIRED DISCHARGE .............................................................. 4
FLEXIBLE DUCTING ................................................................................ 4

2

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when such standard is not applicable, the Standard for
Manufactured Home Installations. (Manufactured Home Sites,
Communities and Set-Ups), ANSI A255.1 and/or CAN/CSA-Z240
MH Series M92 Canadian Standard for Mobile Homes.”
ANSI A 255.1 and/or CAN/CSA-Z240.6.2 MH Series, Mobile
Homes
Ground National Electrical Code ANSI/NFPA 70 and/or CSA
C22.1, Part 1
Park Trailers ANSI 1195

GENERAL FURNACE INSTALLATIONS
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All models can be installed in either a horizontal or vertical
mounting position horizontal installed units have the gas line
positioned on top or rear, vertical installed units have the must
have the vent located at the floor and gas line at right side and
rear.
Always install furnace through an exterior wall.
DO NOT install furnace near tilt-out rooms, slide-outs, doors or
other projection that could obstruct furnace exhaust.
Locate furnace near midpoint of coach for single furnace
applications.
Installation must provide accessibility if any repairs are necessary
to the furnace. Failure to meet this requirement will create
additional labor costs that will be the responsibility of the installer.
DO NOT install vent in areas where projection or door openings
come within 6” of vent opening.
DO NOT install furnace in an area where wires, pipes or other
objects will interfere with installation or operation of furnace.
DO NOT install furnace on material that restricts return air, such
as directly on carpet, or soft material (like vinyl). If you must install
furnace on carpet or soft material, install furnace on cleats, or on
a wood or metal panel extending the full width and depth of
furnace plus minimum clearance to combustibles.
DO NOT use petroleum or citrus type cleaner on plastic parts, as
damage may occur.
CAUTION: Due to the differences in vinyl siding materials this
appliance should not be installed without first consulting with the
manufacturer of siding.
A gas-fired furnace for installation in a residential garage must be
installed so the burner(s) and the ignition source are located not
less than 18 in (457mm) above the floor and the furnace must be
located or protected to avoid physical damage by vehicles.
DO NOT use petroleum or citrus type cleaner on plastic parts, as
damage may occur.

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CLEARANCE TO COMBUSTIBLES

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Floorboards, walls & similar combustible building materials must be