General Service Information; Installation - Suburban NT-12S Service Manual

GENERAL SERVICE INFORMATION

Suburban DYNATRAIL furnaces installed in recreational vehicles are classified as
Forced Draft Furnaces. A forced draft furnace utilizes a sealed combustion chamber that is
vented to the outside atmosphere. The intake air for combustion is also taken from
outdoors and is completely isolated from the exhaust. A motor is used to drive an impeller
wheel to draw intake air into the chamber to support combustion and force the exhaust
gases through the furnace chamber to the outside atmosphere. A second impeller wheel
(driven by the same motor yet totally isolated from the combustion air) is used to circulate
room air across the furnace chamber where it is heated. The blower then forces the hot air
into the living area either through a duct system or through a front grille on the furnace
cabinet on direct discharge models.
There are several differences between a forced air furnace designed for recreational vehicles
and most central furnaces designed for residential use. The major difference is that in a
forced draft combustion furnace, a separate combustion air blower must deliver a
predetermined volume of air into the burner chamber before ignition of the main burner
can occur. Once the main burner flame is established, it is sustained by the air supplied by
the blower.
Suburban furnaces operate on 12-volt DC current that is supplied either by a 12-volt
battery or a converter system. A recreational vehicle furnace that is specifically designed for
"park model" trailers operates on 115 volts AC. These are designed and tested under the
same standards as the 12-volt models.
Suburban forced draft combustion furnaces used in recreational vehicles are designed for
use with Liquefied Petroleum UP) Gas. The operating pressure is between 10.5" - 13.0" of
water column. Although a few recreational vehicle furnaces are approved for use with
natural gas, one should never attempt to convert such a unit to natural gas unless the
conversion is approved by the manufacturer of the furnace.

INSTALLATION

There are several important aspects of the installation that will pertain to all Suburban
forced draft furnaces illustrated in Figures 1, 2 and 3. They are:
1. Venting 2. Return Air 3. Ducting
Refer to the furnace installation manual for each model requirement.
VENTING - By definition of a forced draft combustion furnace, it must be vented to the
outside atmosphere and also draw combustion air from outdoors. Therefore, it is imperative
that the vent be unobstructed and tightly sealed. There must be a separation of the exhaust
and intake air. The vent must be straight. There can be no offsets or turns in the vent. All
vent tubes that connect to the furnace exhaust and intake must overlap a minimum of
1/2". Figure 4 illustrates a typical vent installation.