Reznor RDF Unit Installation Manual - Manual (Page 15)

I-RDF, PN148384R5, Page 15
Step 5. - Install Filters, Block Off Sections and Door Panels
On hoods with filters, position filters and blockoffs on filter racks.
If the systems has an optional dirty filter switch, follow the instructions on page 19 to connect the sensing tubes.
Slide the "door" panels into position on each side of the cabinet section. Fasten each panel with two 1/2" long screws.
Distribution of Makeup Air
Makeup air can be introduced to the building either through distribution ducts or through
controlled pressurization with little or no ductwork. Makeup air should be introduced
and maintained using the lowest possible air velocity. With ductwork distribution, this
is accomplished using a multiplicity of discharge openings over the greatest centerline
distance. When a makeup air system is automatically controlled to maintain a set build-
ing pressure, the entering air will travel naturally toward the relief areas at the perim-
eter walls using the building structure as the distribution ductwork.
Makeup air should enter at the highest point practical. By doing this, the fresh air will
entrain dust laden air at the ceiling and move it toward the point of exhaust. Also, fresh
air directed downward from the roof or ceiling will mix with hot ceiling air resulting in
improved distribution of heat in the building.
Always introduce fresh makeup air so that it moves across the greatest distance within
the room or building before reaching an exhauster.
Proper sizing of warm air ductwork is necessary to ensure a satisfactory heating instal-
lation. The recognized authority for such information is the Air Conditioning Contractors
Association, 1228 17th Street, N.W., Washington, DC 20036. A manual covering duct
sizing in detail may be purchased directly from them.

The type of duct installation depends in part on the type of construction of the
roof (wood joist, steelbar joist, steel truss, pre-cast concrete, etc.) and the ceiling
(hung, flush, etc.).
 Rectangular ducts should be constructed of not lighter than No. 26 U.S. gauge gal-
vanized iron or No. 24 B&S gauge aluminum.
 All duct sections 24" or wider, and over 48" in length, should be cross-broken on
top and bottom and have seams or angle-iron braces. Joints should be S and drive
strip or locked.
 Warm air ducts should not contact masonry walls. Insulate around all air ducts
through masonry walls with not less than 1/2" of insulation.
 Insulate all exposed warm air ducts passing through an unheated space with at
least 1/2" thickness of insulation.
 Duct Supports - Suspend all ducts securely from adjacent building members. Do
not support ducts from unit duct connections.
 Duct Connections - At the heater, use a flexible canvas connection on indoor
units to eliminate vibration transmission.
On outdoor roof curb, down discharge connections, either drop an appropriate
sized and flanged duct into the roof curb prior to setting the unit or attach ductwork
to the bottom flange (using curb dividers as ductwork). If dropping ductwork from
the top, it is recommended that the top perimeter be sealed above and below the
added ductwork. Do not use screws. See ductwork connection locations and siz-
ing, pages 7 and 8.
On outdoor horizontal installations, the ducts can be slid over the flange of the
heater and then sealed for an airtight and watertight fit. On horizontal duct-to-
heater connections and connections to the flanges at the bottom of the curb, use
sheetmetal screws to fasten ducts to the heater flange.
Use stiffening flanges around the perimeter of all duct connections.
 Return Air Duct - The return air duct must be sized for a pressure drop of .5"
w.c. at 2440 fpm in order to balance the system. If not sized properly, there may
be difficulty in obtaining the desired airflow over the burner when the return air
damper is full open.
6.2.2 Evaporative
Cooling Module
If installing an evaporative cooling module, it is shipped separately. Follow the instruc-
tions in the manual with the evaporative cooling module.
6.3 Supply Air
Discharge
Sizing and Installation
of Distribution
Ductwork
(See FIGURE 1, page 4, for
duct opening dimensions.)