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ROOF CURB — For vertical discharge units, assemble or in-
stall accessory roof curb in accordance with instructions
shipped with this accessory. See Fig. 1-3. Install insulation,
cant strips, roofing, and counter flashing as shown. Ductwork
can be installed to roof curb before unit is set in place. Curb
should be level. This is necessary to permit unit drain to func-
tion properly. Unit leveling tolerance is shown in Fig. 1-3.
Refer to Accessory Roof Curb Installation Instructions for
additional information as required. When accessory roof curb
is used, unit may be installed on class A, B, or C roof covering
material.
ALTERNATE UNIT SUPPORT — When the preferred curb
or slab mount cannot be used, support unit with sleepers on pe-
rimeter, using unit curb support area. If sleepers cannot be
used, support long sides of unit (refer to Fig. 4-10) with a mini-
mum number of 4-in. x 4-in. pads spaced as follows:
48AJ,AK,AW,AY020-035 units require 3 pads on each side;
48AJ,AK,AW,AY036-050 units require 4 pads on each side;
48AJ,AK,AW,AY051 and 060 units require 6 pads on each
side. Unit may sag if supported by corners only.
Step 2 — Rig and Place Unit — Inspect unit for
transportation damage. See Tables 1-6 for physical data and
specifications. File any claim with transportation agency.
Do not drop unit; keep upright. Use spreader bars over unit
to prevent sling or cable damage. This unit must be handled
with a crane and can not be handled by a fork truck. Level by
using unit frame as a reference; leveling tolerance is shown in
Fig. 1-3. See Fig. 10 for additional information. Unit operating
weight is shown in Table 2.
NOTE: On retrofit jobs, ductwork may be attached to the old
unit instead of a roof curb. Be careful not to damage ductwork
when removing old unit. Attach existing ductwork to roof curb
instead of unit.
Four lifting lugs are provided on the unit base rails as shown
in Fig. 4-10. Refer to rigging instructions on unit.
POSITIONING — Maintain clearance, per Fig. 4-10, around
and above unit to provide minimum distance from combustible
materials, proper airflow, and service access.
Do not install unit in an indoor location. Do not locate unit
air inlets near exhaust vents or other sources of contaminated
air. For proper unit operation, adequate combustion and venti-
lation air must be provided in accordance with Section 5.3 (Air
for Combustion and Ventilation) of the National Fuel Gas
Code, ANSI Z223.1 (American National Standards Institute).
Although unit is weatherproof, guard against water from
higher level runoff and overhangs.
Locate mechanical draft system flue assembly at least 4 ft
from any opening through which combustion products could
enter the building, and at least 4 ft from any adjacent building.
When unit is located adjacent to public walkways, flue assem-
bly must be at least 7 ft above grade.
ROOF MOUNT — Check building codes for weight distribu-
tion requirements. See Fig. 11. Unit operating weight is shown
in Table 2.
Step 3 — Field Fabricate Ductwork — Secure all
ducts to building structure. Use flexible duct connectors be-
tween unit and ducts as required. Insulate and weatherproof all
external ductwork, joints, and roof openings with counter
flashing and mastic in accordance with applicable codes.
NOTE: Due to width of the horizontal supply and return duct-
work, provisions should be made for servicing of the outdoor
air filters (i.e., catwalk over ductwork).
Ducts passing through an unconditioned space must be in-
sulated and covered with a vapor barrier. Outlet grilles must not
lie directly below unit discharge. The return duct must have a
90-degree elbow before opening into the building space if the
unit is equipped with power exhaust.
To attach ductwork to roof curb, insert duct approximately
10 to 11 in. up into roof curb. Connect ductwork to 14-gage
roof curb material with sheet metal screws driven from inside
the duct.
Follow AMCA (Air Movement and Control Association)
guidelines relating to ductwork connections to the unit. These
guidelines recommend a minimum 2
1
/
2
equivalent duct diame-
ters of straight duct connected to supply air inlet and outlet
openings before any transitions, fittings, dampers, etc. Failure
to adhere to these guidelines may result in system effects which
can impact the unit’s ability to achieve published performance.
Step 4 — Make Unit Duct Connections
48AJ AND AK UNITS — Unit is shipped for thru-the-
bottom duct connections. Field-fabricated ductwork should be
attached to the roof curb. Supply and return duct dimensions
are shown in Fig. 4-6. Air distribution is shown in Fig. 12.
Refer to installation instructions shipped with roof curb for
more information.
48AW AND AY UNITS — Remove shipping covers from
supply and return air openings. Attach field-supplied ductwork
to unit. Connect to the unit with a single duct for all supply
openings and with a single duct for all return openings.
Splitting of the airflow into branch ducts should not be done at
the unit. Sufficient duct length should be used prior to branch-
ing to ensure the air temperatures are well mixed within the
ductwork. See Fig. 7-9 for duct opening dimensions. Secure all
ducts to building structure. Air distribution is shown in Fig. 7-9
and Fig. 13.
Install accessory barometric relief or power exhaust in the
field-fabricated return ductwork. Refer to Step 10 — Position
Power Exhaust/Barometric Relief Damper Hood section on
page 33 for more information.
Instructions continued on page 19.
IMPORTANT: The gasketing of the unit to the roof curb is
critical for a watertight seal. Install gasket with the roof
curb as shown in Fig. 1-3. Improperly applied gasket can
also result in air leaks and poor unit performance.
WARNING
For vertical supply and return units, tools or parts could
drop into ductwork and cause an injury. Install a 90-degree
elbow turn in the supply and return ductwork between the
unit and the conditioned space. If a 90-degree elbow cannot
be installed, then a grille of sufficient strength and density
should be installed to prevent objects from falling into the
conditioned space.