screw heads)

Blower (side
opening)

Vertical /
Horizontal

1/2”

1/2”

1/2”

0”

36 sq. in.

Furnace efficiency rating is a thermal rating determined under
continuous operating conditions, independent of any installation.
Efficiency rate is given at 76% minimum; actual efficiency rating
may be higher.
Return air is supplied through openings in furnace casing. All
return air passages must be kept clear for furnace to function
properly. Refer to Minimum clearance to floorboards, walls &
similar combustible building material.
The total unobstructed return air opening size(s) must not be less
than specified. Failure to meet minimum return air requirements
nullifies furnace warranty.

REQUIRED DISCHARGE
Models
AFM (16)(20)
AFM (25)(30)(35)
Horizontal Bottom
Vertical Bottom

System
4” Ducts
Horizontal
Bottom
Vertical
Bottom

Required Discharge Area
24 in2
36 in2
48 in2
48 in2

AFMD16

AFMD20

AFMD25
AFMD30
AFMD35

2

2

3

4 x 10

4 x 10

4 x 10

5 x 9-3/4

5 x 9-3/4

5 x 9-3/4

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







Spacing of 1/4” to ducting within 3 feet of furnace must be
provided unless UL listed wire bound vinyl ducts are used. All
ducting material used to be rated for continuous use at minimum
of 200°F.
Clearances are specifically for plywood or similar building
materials surrounding the furnace (i.e. Furnace should not be
located under furniture or in a closet space where clothing or
other material could be located).
To install without adding the 36 sq. in. cutout on the blower side
supply the unit (blower side) with 2” clearance full length of the
unit.

3

16,000

20,000

25,000

3000 fpm
3000 fpm
3500 fpm
Total fpm= feet per minute readings

30,000

35,000

4000 fpm

5500 fpm

FURNACE INSTALLATION

Remove furnace from box

Remove vent assembly supplied with furnace

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.

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 17” wide by
8.5” 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 on small vent
installations.





WALL CUTOUTS
(Standard door square corner and Flush Door requires 3/4” radius
corners)
A
B
D
Side Wall Cutout
3-1/2” Dia.
Small Vent
Max
Standard Door
(horizontal or
17” Max
7-1/2” Max
vertical)
Flush Door
(horizontal or
18-1/4” Max 9-1/8” Max
vertical)

Proper duct installation is critical to proper operation of the
furnace. When installing ducts, use materials rated for continuous
use at 200°F.
Each 4-inch duct opening provides 12 in2 of discharge area.
Provide an extra 12 in2 of non-closeable duct discharge area for
each closeable register used.
Ducting into 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 an air temperature rise of
100°F-130°F. Also see air flow check section.

FLEXIBLE DUCTING












Follow ducting configurations shown.
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)

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 proper 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 registers the total reading
should not be less than what is shown in table below for each
BTU size.
If readings are below the table values airflow can be improved by
adding ducts or reducing/eliminating restrictions in the system.

4

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

STANDARD DOOR INSTALLATION







To prevent moisture from entering the inside of the coach, apply
RTV type sealant to all sealing areas.
The door bezel must fit tightly to sidewall to prevent water
leakage.
Doors are designed to allow water drainage in either horizontal or
vertical installations. Proper location of vent assembly is important
for proper exhausting of fumes and proper function of furnace.
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.

SMALL VENT INSTALLATION



To prevent moisture from entering inside of coach, apply RTV
type sealant to the back of the bezel flange of the vent part.
Vents are designed to allow water drainage when installed
correctly.

Use of foil tape as
alternate sealing
method is acceptable

HARD DUCTING SYSTEM
1.
1.
2.

3.
4.
5.
6.

Locate the furnace vent cutout location.
Drill a 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 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.

2.
3.

4.
5.
6.
7.
8.
9.

5

Locate where furnace will be installed and cut an 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.
Apply RTV type sealant to entire back flange of bezel creating a
complete seal.
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.
Secure bezel to furnace casing with 6 screws provided or use
equivalent type screws.
Push furnace and bezel back tight against side wall and secure
with 14 screws, and remove excess caulking..
When installing bezel DO NOT deform bezel if cutout hole is too
large as this will cause water-sealing issues.
Connect the gas line to the valve see section on gas connection.
Secure furnace to floor with mounting legs and screws provided
or equivalent type.
Connect the electrical wiring see wiring section.

10. Fasten door and vent with 10 screws provided or equivalent type.
FLUSH DOOR INSTALLATION





To prevent moisture from entering inside of coach, apply RTV
type sealant to all sealing areas.
The door bezel must fit tightly, to prevent water leakage.
Doors are designed to allow water drainage in either horizontal or
vertical installations. Proper location of vent assembly is important
for proper exhausting of fumes and proper function of furnace.
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.

1.
2.

Locate and cut opening in side wall where unit will be installed.
Flush mounted door systems require that the furnace be installed
on a 1” high platform for the door cutout to be level with the floor
surface. If not the sidewall can be routed out across the bottom to
the depth of the bezel to create a pocket area.
3. Apply RTV type sealant to entire back flange of bezel creating a
complete seal.
4. Secure bezel by inserting bezel into wall cutout and securing
through the 10 mounting tabs to the side wall framing. Make sure
that the bezel is tight against the exterior side wall.
5. Connect the gas line to the valve and push the gas line plug into
casing opening.
6. The door bezel must fit tightly against the exterior sidewall to
prevent water leakage.
7. Remove excess sealant from around bezel and visually inspect
bezel to make sure it is completely sealed.
8. Secure furnace with mounting legs provided.
9. Connect the electrical wiring see wiring section.
10. Fasten door and vent with 6 screws provided.

WARNING
FIRE OR EXPLOSION
Never check for leaks with an open flame. Turn on the gas and apply
soapy water to all joints to see if bubbles are formed.
GAS CONNECTION
Propane Gas Pressure Test

The furnace and any individual shut-off valve must be
disconnected from gas supply piping system during pressure
testing of system at test pressures of more than 1//2” PSI.

Before furnace is connected, piping systems are to be tested to
be leak free. The test must maintain air pressure of a least 6” of
mercury or 3 PSI for at least 10 minutes.

The entire piping system is to be adjusted to 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 test
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.

HARD DUCT SYSTEMS
When designing hard duct systems:

Undersized ducting will cause high temperature limiting.

Oversized ducting will cause inadequate air flow from registers.

When hard ducting is 1-1/2” in depth, an additional flex duct may
be needed to maintain air flow requirements.

DO NOT install floor registers within 2 feet of return air openings.
See ducting option from casing top and bottom areas. Hard
ducting must be sealed to the furnace and floor to insure proper
operation of the appliance.

Units can be installed as bottom discharge systems in either
horizontal or vertical position.
FLOOR DISCHARGE CUTOUTS
1.
2.
3.

4.

5.
6.
7.

Remove bottom discharge plate or side, these ducting option
must be connected to a floor ducting system.
The drawing shows the use of a gasket and plenum plate for
attaching furnace to the flooring. See parts list for order number.
Other methods of sealing furnace to the floor are acceptable as
long as clearances and seals meet requirements of clearances
and temperature.
Fasten plenum plate bend tabs over floor cutout. (If a gasket and
plenum plate is not used seal furnace to hard ducting system with
approved tape making sure seal is airtight) Continue with step 5.
Position gasket on plenum over opening.
Set furnace on gasket; make sure gasket remains in position.
Additional flex ducting can also be used to maintain correct static
pressure.

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 chemical reaction of
propane (LP) gas. DO NOT put sealing compound on flare fittings
Remove grommet plug from furnace. After inserting gas line
through grommet plug and connecting to valve re-install grommet
plug, this is a required air seal. (DO NOT CUT)
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,
torque fitting to 20-22 ft. lbs.

ELECTRICAL CONNECTIONS
1.

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

CAUTION
PROPERTY DAMAGE
Units with 12 volt connection are for low-voltage battery or direct
current only.
Do not connect to 120 or 240 volts AC.

CAUTION
PROPERTY DAMAGE
This furnace is designed for negative ground 12 volts DC only. DO
NOT attempt to alter furnace for a positive ground system or connect
the furnace directly 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
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
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
10**
40
8**
55
6**
75
4**