provided the full length and width of unit. Spacing is based on installed
position when installed horizontally bottom is bottom. When installed
vertically bottom becomes right side.



clearances

Top

Sides

Rear

Bottom (to
screw
heads)

Blower (side
opening)

Vertical /
Horizontal

1/2”

1”

1/2”

0”

36 sq. in.

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 right side of unit (blower side) with 2” clearance full
length of the unit
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 DUCTING
All ducts in the table are four-inch ducts except for bottom discharge as
noted. Two-inch ducts cannot be used in place of four inch.
A bottom discharge requires no additional ducting; additional ducts can
be added if required. Vertically installed units can also be bottom
discharge when right side cover panel has been removed additional
duct can be added if required.
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. When using side ducts rear duct
openings will give the best performance.

3

 Horizontal Bottom Discharge: This installation is for horizontally
installed units and can be used with the addition of one duct any
location except the top two.
 Vertical Bottom Discharge: Installation of the furnace in a
vertical mounting position can be used with the addition of one
duct any location except the top two.

FLEXIBLE DUCTING
When designing flexible duct systems:

Follow ducting configuration shown

Avoid sharp bends or crushed ducts.

Stretch all ducts and run them directly to outlets, keeping quantity
and angles of bends to a minimum.

Remove knockout plate from desired outlets. If a knockout is
removed accidentally a cover plate can be purchased.

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).

REQUIRED DISCHARGE
Models
AFL (35)(40)
Horizontal Bottom
Vertical Bottom

Required Discharge Area
36 in2
48 in2
48 in2

System

AFLD35

4” Duct

3

3

3

3

4x10

4x10

4x10

4x10

5x9-3/4

5x9-3/4

5x9-3/4

5x9-3/4

Bottom plus
4”duct min
Vertical
Bottom

AFLD40

AFLA35

AIR FLOW CHECK

AFLA40





*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 high temperature limit. Extra ducting can be used to
help correct this condition due to restriction or bends in duct
work.



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 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 reduce restrictions in the system.
35-40 DC

35-40 AC

4600 fpm
5000 fpm
Total fpm= feet per minute readings
FURNACE INSTALLATION












The furnace should always be installed level (front to back, side to
side) to prevent water intrusion into the interior.
Set aside venting and outer door parts for installing on the outside
of coach.
NOTE to assure sufficient return air to circulating blower maintain
specified clearances.
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 service suggested opening size 17” wide by 91/2” height.
Remove knockouts from furnace and install duct adapters for side
discharge by inserting back flange over casing and inserting tab
into square notch, then twist adapter 90°.
Insert furnace into cabinet opening and secure with two screws
through casing legs to floor. Units are secured by door or vent
systems through the coach sidewall.
Attach flexible ducting over duct adapters and secure. All flex
ducting requires rating of 200°F.
Run ducting to locations keeping bends and excess ducting to a
minimum and secure to registers.
Connect wiring to located on the top of the furnace. See wiring
connection section.
Connect gas line to top or rear of furnace. See gas connection
section.

SIDEWALL CUTOUT





Maximum exterior wall thickness 0” to 2-1/2” an optional vent kit can be
purchased to extend the vent usage to 3” wall thickness for small vent
installations
WALL CUTOUT

Proper duct installation is critical to operation of 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 air rise of 100°F-130°F. Also
see air flow check section.

(Flush Door requires 3/4” radius corners)

Flush Door (corner cut requires
3/4” radius) (horizontal or vertical)



4

A

B

C

18-1/4”

11 1/8”

20”

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




1.
2.

3.
4.

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.

5.
6.
7.
8.
9.

1.
2.
3.
4.
5.

6.

Locate were furnace vent cutout will be made.
Drill 3-1/2” diameter hole through sidewall of coach.
Insert furnace from inside of coach, lining up hole in wall with vent
in furnace.
Apply sealant to back of vent panel extension (plastic part).
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) provided at back of casing. For vertical
units casing legs can be positioned for placement to secure
furnace



Locate and cut-hole location in side wall were unit will be
installed.
Flush mounted doors system requires that the furnace be install
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.
Apply RTV type sealant to entire back flange of bezel creating a
seal area.
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 side wall.
Connect the gas line to the valve and push the gas line plug into
casing opening.
The door bezel must fit tightly against sidewall to prevent water
leakage.
Remove excess sealant from around bezel and visually inspect
bezel to make sure it is completely sealed.
Secure furnace with mounting legs provided.
Fasten door and vent with 6 screws provided

Use of foil tape as
alternate sealing
method is acceptable

HARD DUCTING SYSTEMS
When designing hard ducting systems:

Undersize ducting will cause high temperature limiting.

Oversize ducting will cause inadequate air flow from registers

When hard ducting is less then 1-1/2” in depth additional flex
ducting may be needed to maintain static pressure requirements.

FLUSH DOOR INSTALLATION


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.

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.

5







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.





HORIZONTAL FLOOR DISCHARGE CUTOUT
1.
2.

3.

4.

5.
6.
7.

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 maintained 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.

Remove bottom discharge plate, this ducting option must be
connected to a floor ducting system.
The drawing shows the use of a gasket (F) and plenum plate (E)
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 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).
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.

CONVERTIBLE GAS CONTROL







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
Gas Pressure Test

The furnace and any individual shut-off valve must be
disconnected from gas supply piping system during and pressure
testing of system at test pressures of more than 1//2” PSI.

AC model units come equipped with a convertible gas control.
Each unit is supplied with two main burner orifices. One will be in
place; the other will be attached to the blower housing cover.
Each orifice will be clearly marked with a drill size as shown
below.
The pressure settings of the convertible valve are set for natural
gas NAT 3.5” WC or LP 10.5” WC and are not adjustable.
Use Loctite* #RC609 or some other thread lock sealant on orifice
threads when installing a new orifice.
A 1/8” NPT plug is provided upstream of gas connections for
checking gas pressure.
GAS
TYPE

BTU/HR

LINE
PRESSURE

REG. PLUG
SETTING

DRILL
SIZE

Propane
(LP)

40,000

11” WC

10.5” WC

49P

Natural
(Nat)

40,000

7” WC

3.5” WC

#30

Propane
(LP)

35,000

11” WC

10.5 WC

#51

Natural
(Nat)

35,000

7” WC

3.5” WC

#30

*WC= Water Column

6

CAUTION
PROPERTY DAMAGE
On 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