107272-UIM-B-1105
10
Unitary Products Group
DFAH Furnaces:
If a matching cooling coil is used, it may be placed directly on the fur-
nace outlet and sealed to prevent leakage. Follow the coil instructions
for installing the supply plenum. On all installations without a coil, a
removable access panel is recommended in the outlet duct such that
smoke or reflected light would be observable inside the casing to indi-
cate the presence of leaks in the heat exchanger. This access cover
shall be attached in such a manner as to prevent leaks.
RETURN AIR REQUIREMENTS
Closet Installations
Additional Requirements
Additional requirements for floor and ceiling return system for closet
installed sealed combustion heating appliances are given in the next
paragraph.
Floor or Ceiling Return Air System
Listed in the next paragraph are the conditions to be met by Manufac-
tured Home Manufacturers to have U.L. acceptance of in-floor or ceiling
return air systems of closet installed direct vent forced air heating appli-
ances for Manufactured Homes to be sold in the United States.
1.
The return air opening into the closet, regardless of location, is to
be sized not less than 16” X 24” (40.6 cm x 101.6 cm).
2.
If the return air opening is located on the floor of the closet (versus
the vertical front or side wall), the opening is to be provided with
means to prevent its inadvertent closure by a flat object placed
over the opening.
3.
The cross sectional area of the return duct system (when located
in the floor or ceiling of the manufactured home) leading into the
closet is to be not less than 16” X 24” (40.6 cm x 101.6 cm).
4.
At least one register is to be located where likelihood of its being
covered by carpeting, boxes, and other objects is minimized.
5.
Materials located in the return duct system have a flame spread
classification of 200 or less.
6.
Non-combustible pans having 1” (2.5 cm) upturned flanges are
located beneath openings in the floor return duct system.
7.
Wiring materials located in the return duct system conform to Arti-
cle 300-22 (B&C) of the National Electrical Code (NFPA-70).
8.
Fuel piping is not run in or through the return duct system.
9.
The negative pressure in the closet as determined by test with the
air circulating fan operating at high heating speed and the closet
door closed is to be not more negative than minus 0.05 inches (1.2
kPa) water column.
10. For floor return systems, the manufactured home manufacturer 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:
BLEND AIR INSTALLATIONS
If a blend air ventilation system is installed, the 5” (12.7 cm) diameter
knockout in the top cover must be removed. The blend air damper is to
be placed on the top cover and secured with screws as shown in Figure
14. The power wires for the Blend Air Damper are inserted through the
7/8” (2.22 cm) hole in the top cover. The wires to the Blend Air Damper
will be connected as shown in Figure 24. Refer to the Blend Air Installa-
tion Manual to complete the installation.
SECTION III: FILTERS
FILTER INSTALLATION
All applications require the use of a filter. A standard air filter is located
in the return filter rack on the louvered door. The air filter(s) must be
replaced with air filter(s) that are the same size and same type.
Replacement filter size is shown in Table 5.
Downflow Filters:
There are two types of downflow filter racks.
1.
FURNACE FILTER RACK: A return filter rack is with two standard
throwaway type filters are supplied on all models. The return filter
rack is located on the inside of the louvered door. This type of filter
rack is designed for two standard air filters only. Pleated Media or
Washable Filters cannot be used in this filter rack because they
cause too much pressure drop causing a reduction in airflow.
2.
EXTERNAL RETURN FILTER GRILLE: The second type is an
external return air filter grille that can only be used in applica-
tions where the furnace is installed in a closet. This type of fil-
ter grille is typically installed in a closet door or wall with the filters
located within 12" (30.5 cm) of the return air opening of the fur-
nace. There must be a minimum clearance of 6" (15.2 cm)
between the front of the furnace and the closet door and/or the fur-
nace and the filter grille to prevent the return air flow from being
obstructed. Refer to Table 1 Unit Clearances to Combustibles.
a.
If the standard throwaway filter are used the external filter
grille must have a minimum area of 540 in² (3483 cm²) which
would equal a 15" X 36" (38.1 cm x 91.4 cm) filter grille.
b.
If the Pleated Media or Washable Filters are used the exter-
nal filter grille must have a minimum area of 684 in² (4413
cm²) which would equal a 18" X 38" (38.1 cm x 91.4 cm) filter
grille. The increased area is to reduce the pressure drop
across the air filter.
c.
Consideration should be given when locating the return filter
grille for maintenance.
d.
Any filter that has a large pressure drop should be checked to
be sure the pressure drop caused by the air filter will not pre-
vent the furnace from operating within the rise range, speci-
fied on the rating plate and in Table 8. If the furnace does not
operate within the specified rise range then a larger air filter
or an air filter that has a lower pressure drop must be
installed.
HAZARD OF ASPHYXIATION, DO NOT COVER OR RESTRICT
FLOOR OPENING.
FIGURE 14: Floor Installation
TABLE 5: Filter Sizes
Input / Output
BTU/H (kW)
CFM
(m
3
/mm)
Top Return
Filter In. (cm)
66 / 53 (19.34 / 15.53)
1050 (29.73)
(2) 14 x 20 (35.56 x 50.8)
84 / 67 (24.62 / 19.64)
1250 (35.40)
(2) 14 x 20 (35.56 x 50.8)
WARM AIR DUCT
DUCT CONNECTOR
Floor
Blend Air
Flex Duct
Blend Air
Damper
