also be used when using four-inch front option. Front duct must not
exceed 12”.

Floorboards, walls & similar combustible building materials must
maintain clearances given and must be provided the full length and
width of the unit. Spacing is given based on the installed position of the
furnace.

Clearances

Top

Sides

Rear

Bottom (to
screw
heads)

Blower (side
cabinet
opening)

Vertical or
Horizontal

1/2”

1/2”

1/2”

0”

16 sq. in.

FOR OPTIMAL PERFORMANCE:
Use the following ducting recommendations. Top Duct is used only in
addition to these requirements and is not allowed to be used until
these requirements are met. Additional ducting when added will reduce
the airflow through the ducting and improper ducting could cause poor
heating and or cycling on high temperature limit.
 Horizontal or Vertical 4” Ducting; when using 4” ducting one
duct from each side must be used. Unless the front discharge is
used with either the 5” duct and grill or optional 4” ducting.
 ‘No Bottom Discharge system allowed”.
DISCHARGE AND DUCTING
Model
AFSA (12)
AFS (12) (16) (20)

Side Ducts
Front with Side
Ducting
Front Only 5”
duct
Front Only 4”

3

AFSD12
2

Required Discharge Area
FRONT GRILL or 15 in2
24 in2
Models
AFSD16
AFSD20
AFSAD12
2
2
X

1

1

1

X

1

1

1

1

2

2

2

X


*Note the table is for minimum requirements and should in most cases
allow the unit to operate correctly. If unit burner cycles on and off on
high temperature limit extra ducting can be used to help correct this
condition due to restriction or bends in duct work.




















Proper duct installation is critical to proper operation of the
furnace. When installing ducts, materials must be rated for
continuous use at 200°F.
Each 4-inch duct opening provides 12 in2 of discharge area. The
minimum for this furnace is 24 in2. If closeable registers or 2”
ducts are used additional ductwork or a front grill system is
required.
Ducting in dead air space with no return air, such as holding tank
areas, does not count toward achieving minimum discharge
requirements.
Adjust ducting installation to obtain air rise of 100°F-130°F for
optimum performance.
Do NOT install heat register’s closer than 24” to return air system.

DO NOT mix assemblies with other units, each model has a
specific vent baffle size to operate correctly, see sticker on vent
assembly.
Remove knockouts in locations that will be used and install
adapters.
The furnace should always be installed level (front to back, side to
side) to prevent water build up into the interior of the vent area.
Units can be installed with or without the interior grill. If grill is not
used a minimum of 35 in2. of free return air must be provided.
If units are installed using the small outside vent system, access
to the inside of the coach must be provided directly in front of the
unit to remove for servicing suggested opening size 12-1/2” wide
by 8-3/8” height.
Secure unit with two brackets and screws provided at the rear of
the unit through holes provided.
Attach flexible ducting over duct adapters and secure.
Run ducting to locations keeping bends and excess ducting to a
minimum and secure to registers.
Connect wiring to furnace see wiring connection section.
Connect gas line see gas connection section.

SIDEWALL CUTOUT
Maximum exterior wall thickness 0” to 2-1/2”. Optional vent kit can be
purchased to extend the vent to a 3” wall thickness only on small vent
installations.
WALL CUTOUTS
Standard Door square corners for proper sealing.
Venting Option
A







Follow ducting configuration given
Avoid sharp bends, deep sags or crushed ducts.
Stretch all ducts thoroughly and run them directly to outlets,
keeping number of angles of bends to a minimum.
Remove knockout plate from desired outlets. If a knockout is
removed accidently cover plates can be purchased.
Unused knockouts MUST be covered.
Attach a duct adapter by inserting flange over casing hole, locking
the tab into casing slot and turning adapter 90°
Attach and secure four-inch flexible duct to adapter(s)
Run duct(s) to desired location within RV, secure to register(s)

-

-

Standard Door (exterior)

12-1/2” Max

7-1/2”
Max

Front Grill (interior cabinet)

11-0”
Max

7-1/4”
Max

Front Grill Trim Ring (interior
cabinet)

12-1/2”
Max

8-3/4”
Max




DO NOT oversize hole – over sizing can result in water leakage.
Zero clearance around air intake cutout for best sealing condition.

AIR FLOW CHECK






Appliance is tested to a temperature rise as specified on the
Rating Plate. After installation of the furnace and duct system is
completed, adjustment to obtain a temperature rise should be
made.
The table below is a reference to maintain maximum operation of
the appliance when checking temperature rise is not possible.
Airflow measurements made at each register, the total reading
should not be less than what is shown in the table below for each
BTU size.
If readings are below the table values airflow can be improved by
adding ducts or by reducing restrictions in the system.
AFSA12

AFS12

AFS16

AFS20

Not Required

1650 FPM

1650 FPM

1800 FPM

*total FPM= feet per minute
FURNACE INSTALLATION

Remove furnace from box

Remove vent assembly supplied with furnace
SMALL VENT INSTALLATION

4

D
3-1/2”
Dia. Max

Small Vent (exterior)

FLEXIBLE DUCTING SYSTEMS




B




To prevent moisture from entering inside of coach wall, apply RTV
type sealant to the back of the vent panel extension before
installing through wall into furnace.
Vents are designed to allow water drainage when installed
correctly.

Use of foil tape as alternate
sealing method is acceptable

1.
1.
2.

3.
4.
5.

6.

Locate were furnace will be installed and cut a hole opening as
shown through the side wall where unit will be installed. Furnace
and components MUST be protected from construction tools and
debris during installation.
2. Apply RTV type sealant to entire back flange of bezel creating a
complete seal
3. Pull furnace forward through cutout about 1” inch, slip bezel (note
word TOP on bezel) around casing until flush with front edge of
the casing.
4. Secure bezel to furnace casing with 4 screws provided or
equivalent type screws.
5. Push furnace and bezel back tight against wall, secure with 14
screws, and remove excess caulking.
6. When installing bezel DO NOT deform bezel if cutout hole is too
large as this will cause water-sealing issues.
7. Connect the gas line to the valve see section on gas connection.
8. Secure furnace to floor with mounting legs and screws provided
or equivalent type screws.
9. Connect the electrical wiring see wiring section.
10. Fasten door and vent with 8 screws provided or equivalent type
screws.

Locate the furnace vent cutout location.
Drill 3-1/2” diameter hole through sidewall of coach. Installer
MUST Protect the furnace and components from construction
tools and debris during installation.
Insert furnace from inside of coach, lining up hole in wall with vent
in furnace.
Install vent assembly, vent panel extension must be inserted into
air intake tube. Secure vent to wall with 4 screws provided.
Vent can extend a maximum of 2-1/2” to allow for different wall
thickness. Vent assembly must maintain overlaps of 1-1/4” on
exhaust tube and 1/2” on air tube. DO NOT exceed maximum wall
thickness.
Secure furnace to floor with legs and screws (equivalent type
screws can also be used) through holes provided at back of
casing. For vertical units casing legs can be positioned by using
alternate holes for placement to secure furnace.

STANDARD DOOR INSTALLATION







To prevent moisture from entering the coach, apply RTV type
sealant to total back of bezel trim ring before installing.
The door bezel must fit tightly to sidewall to prevent water
leakage.
Door design allows water drainage in either horizontal or vertical
installations.
NOTE: RTV type sealant must be applied to the bezel and casing
at the bottom right side to prevent possible water wicking into the
coach. See drawing for areas that must be sealed once bezel is in
place.
Insert vent assembly through door making sure tube goes into the
chamber tube. Proper overlap of the vent tube must be a
minimum of 1-1/2” for proper function and exhausting of furnace.

INTERIOR GRILL







5

Non Service Install: To install grill cut an 11” x 7-1/4” hole into
the cabinet for non-removable furnace installation using Kit. This
kit also supplies the required return air grill.
Service Install: To install grill as an access for removal of
furnace cut a 12-1/2” x 8-3/4” hole into the cabinet from the floor
up. This installation requires Kit. This kit also supplies the
required return air grill.
Optional 4” Front Duct: To install with optional 4” duct an
adapter is required to allow connection of 5” hole to standard 4”
duct and standard round register. See required ducting section for
requirements.
Discharge air from the round grill louver can be directed 360° by
rotating louver.

1.

2.

3.

4.
5.
6.

Connect gas line to the fitting located on the valve through hole in
top of casing or if supplied with an extended manifold at the rear
of the furnace.
Be sure all male pipe threads, other than flare fittings, are treated
with a sealing compound resistant to the action of propane (LP)
gas. DO NOT put sealing compound on flare fittings
Remove grommet plug from furnace. After inserting gas line
through gas plug and connecting to valve re-install gas plug this is
a required air seal.
Insert gas line through grommet plug (DO NOT CUT GROMMET).
Connect gas line inside furnace casing immediately ahead of gas
control valve or at the rear when extended manifold is supplied.
Use two wrenches to hold brass fitting and flare nut when
tightening gas line to brass fitting. DO NOT twist valve assembly.
DO NOT twist valve assembly, torque fitting to 20-22 ft. lbs.

ELECTRICAL CONNECTIONS

WARNING
INJURY OR PROPERTY DAMAGE
 Label all wires before disconnecting for servicing. Wiring errors can
cause improper and dangerous operation. Verify proper operation
after servicing.
 Disconnect electrical power before servicing.
1.
2.

3.
4.

5.

Locate cabinet cutout location and cut hole per type of installation
being used.
Install adapter by removing the large knockout from the rear of the
casing and attach the 5” duct adapter or optional 5” to 4” inch
adapter.
Fasten 5” duct to the adapter and to the back of the interior grill
and secure.
On installations with 1” or less space between 5” adapter and grill,
the grill can be inserting directly into the adapter to complete the
connection.
Secure grill to cabinet by fastening with screws.

CAUTION
PROPERTY DAMAGE
This connection is for low-voltage battery or direct current only. Do not
connect to 120 or 240 volts AC.
INSTALLATION AND SAFETY CODES

USA and Canada – follow all applicable state and local codes in
the absence of local codes or regulations, refer to current
standards of:

ANSI/NFPA 1192 Recreational Vehicles Code and ANSI/RVIA LV
Low Voltage Systems in Conversion and Recreational Vehicles

WARNING

POWER SUPPLY

FIRE OR EXPLOSION
Never check for leaks with an open flame. Turn on the gas and apply
soapy water or leak detect solution to all joints to see if bubbles are
formed.

Atwood Mobile Products highly recommends the use of an electronic
(solid-state) converter with clean power output. This will assure
extended life of the electronic controls and motor beyond typical linear
converter applications.

PROPANE GAS CONNECTION
Propane Gas Pressure Test

The furnace and any individual shut-off valve must be
disconnected from gas supply piping system during any pressure
testing of system at test pressures of more than .5 PSI.

Before furnace is connected, piping systems are to be tested to
be leak free. The test must maintain air pressure of at least 6” of
mercury or 3 PSI for at least 10 minutes.

The entire piping system is to be adjusted to and maintain a
pressure of 10” to 13” W.C. when all appliances are in operation.

Test gas connections for leakage with soapy water or a leak
detect solution.

If local codes allow the use of a flexible gas appliance connector,
always use a new listed connector. Do not use a connector which
has previously serviced another gas appliance.

CONDUCTOR SIZING
Table 1
OVERCURRENT PROTECTION (No Wire Bundling Restrictions)
Wire Size
Ampacity
Wire Type
20
3
Stranded only
18
6
Stranded only
16
8
Stranded only
14
15
Stranded only
12
20
Stranded only
10
30
Stranded only
8
40
Stranded only
6
55
Stranded only
4
75
Stranded only
2
100
Stranded only

6

Table 2
OVERCURRENT PROTECTION
*Not More Than Seven Wires Per Harness
**Not More Than Three Wires Per Harness
AWG OR SAE
Maximum Ampacity
Conductor Size
at Conductor
(Gage)
Insulation
Temperature Rating
of 90°
20*
5
18*
7.5
16*
10
14*
17.5
12*
22.5