19
rETurn air
The cabinet that the furnace may be installed in will have louvers or openings for the return air back to the furnace. When
the furnace is installed, it is imperative that the return air louvers on the furnace cabinet opening are not obstructed.
usually, these furnaces are installed under a counter, sofa or bed in order to be out of the way. A grille or opening must
be built into the cabinetry or into the base area of the sofa or bed. Return air from the living area of the trailer is drawn in
through the grille and into the return air openings in the furnace cabinet. Figure 20 illustrates the return air circulation of the
furnace.
Note: Refer to the installation manual for the minimum return air area for your specific furnace model.
insufficient return air will cause the furnace to overheat and cycle on limit. Another symptom of a return air problem is:
1. Furnace seems to run continuously in an effort to satisfy the thermostat.
0" TO SPACER
0" TO SPACER
OPENING FOR RETURN AIR
SPACER BUMPS
OPENING FOR
RETURN AIR
MAINTAIN A 1/4" INCH CLEARANCE
WHERE DUCTS PASS THROUGH
A CABINET WALL. UL LISTED DUCT
MATERIALS CAN BE 0" CLEARANCE.
THE TOTAL, FREE, UNOBSTRUCTED RETURN AIR OPENING
TO THE FURNACE MUST NOT BE LESS THAN THE MINIMUM
SPECIFIED.
SPACER BUMPS
FURNACE
Figure 20
SF 20F/25F/35F/42F
DuCTinG
Suburban furnaces require that a minimum duct area be maintained throughout entire duct system including through
the register. it is very important to adhere to the minimum duct area in order to keep the furnace from cycling on high
limit and to assure proper operation of the sail switch (sometimes referred to as a microswitch.)
NOTE: (Refer to the
installation manual for the minimum ducted square inches area for
each model.)
NOTE: Ducts terminating in a dead air space (like holding tank
compartments or cargo areas (Toy Boxes) with no means for return
air recirculation should not be counted in the required duct area.
Also, ducts 2” in diameter or smaller should not be counted in the
required duct area.
When installing a duct system, avoid making a lot of turns. The straighter
the duct system, the less the resistance to air flow and the better the
performance of the furnace.
Avoid making sharp turns in the duct system. Sharp turns will increase
the static pressure in the plenum area of the furnace and could cause the
furnace to cycle on limit.
The duct connections to the furnace cabinet should be tight to eliminate
any heat loss which could result in overheating of the component parts
on the furnace as well as a reduction in the heated air flow through the
duct work.
Figure 21
