19
RETURN AIR
furnace. Note: Refer to the installation manual for the minimum return air area for your specic furnace model.
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
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.
furnace to cycle on limit.
Figure 21
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