8
C. The cross-sectional area of the return duct system
(when located in the floor or ceiling of the mobile home)
leading into the closet is to be not less than that of the
opening specified on the appliance’s rating plate.
D. The total free area of openings in the floor or ceiling reg-
isters serving the return-air duct system is to be not less
than 150% of the size of the opening specified on the
appliance’s rating plate. At least one such register is to
be located where likelihood of its being covered by car-
peting, boxes, and other objects is minimized.
E. Materials located in the return duct system have a
flame spread classification of 200 or less.
F. Non-combustible pans having one-inch upturned
flanges are located beneath openings in the floor re-
turn duct system.
G. Wiring materials located in the return duct system con-
form to Article 300-22 (b&c) of the National Electric
Code (ANSI C1 / NFPA-70).
H. Gas piping is not run in or through the return duct sys-
tem.
I.
The negative pressure in the closet as determined by
test with the air-circulating fan operating at high heat-
ing speed and the closet door closed is to be not more
negative than minus 0.05-inch water column.
J. For floor return systems, the mobile home manufactur-
er or installer shall affix a prominent marking on or near
the appliance where it is easily read when the closet
door is open. The marking shall read:
WARNING
HAZARD OF ASPHYXIATION
Do not cover or restrict floor opening, or equivalent.
AIR DISTRIBUTION SYSTEMS
For proper air distribution, the supply duct system shall be
designed so that the static pressure does not exceed the
listed static pressure rating on the furnace rating plate.
Three typical distribution systems are illustrated in Figure 4.
Location, size and number of registers should be selected
on the basis of best air distribution and floor plan of the
home.
Figure 4
A
Single trunk duct
Dual trunk duct
Transition duct
*
B
S
1
Crossover Duct must be centered directly
under
furnace.
S
2
Use 12” Diameter Round or equivalent insulated Flex-duct only.
S
3
Terminate Flex-duct (opposite furnace) in the
center
of the trunk duct.
S
4
Flex-duct material must be pulled tight — No Loops or unnecessary dips —
Air Flow may be impeded.
1
2
3
4
B *
Dual trunk duct with crossover connector
Crossover
C
Transition Duct with Branches
Branches
