Suburban DD-17DSI, Service Manual

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18
DUCTING
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 ductwork.
Figure 20