10
Duct System Installation
The duct system should be sized to handle the design
airflow quietly. Refer to Figure for horizontal duct
system details or figure 8 for vertical duct system details.
A flexible connector is recommended for both discharge
and return air duct connections on metal duct systems to
eliminate the transfer of vibration to the duct system. To
maximize sound attenuation of the unit blower, the supply
and return plenums should include internal fiberglass
duct liner or be constructed from ductboard for the first
few feet. Application of the unit to uninsulated ductwork
in an unconditioned space is not recommended, as the
unit’s performance will be adversely affected.
At least one 0° elbow should be included in the supply
duct to reduce air noise. If air noise or excessive air flow
is a problem, the blower speed can be changed. For
airflow charts, consult submittal data for the series and
model of the specific unit.
If the unit is connected to existing ductwork, a previous
check should have been made to insure that the ductwork
has the capacity to handle the airflow required for the
unit. If ducting is too small, as in the replacement of a
heating only system, larger ductwork should be installed.
All existing ductwork should be checked for leaks and
repaired as necessary.
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Figure 6: Horizontal Condensate Connection
HORIZONTAL INSTALLATION
CAUTION!
Ensure condensate line is
pitched toward drain 1/4” per foot [10mm per
46cm] of run.
Condensate Piping – Horizontal Units
Units are typically installed directly above each other on
successive floors with condensate drains located near
the units. Attach the unit condensate drain connection
to the building condensate drain with a flexible, non-
pressure-rated /4 inch [1mm] ID plastic hose. Insure
that the hose is without kinks to maintain unobstructed
flow of condensate from the unit to the drain. Verify that
condensate line is pitched towards the drain 1/4” per foot
(10mm per 46cm) of run.
Pitch the unit toward the drain as shown in Figure to
improve the condensate drainage. On small units (less
than .5 tons/8.8 kW), insure that unit pitch does not
cause condensate leaks inside the cabinet.
The horizontal run of a condensate hose is usually
too short to cause drainage problems. However, the
horizontal run of the condensate line should be pitched
at least 1 inch for every 10 feet [10mm per 116cm] of run
in the direction of flow to insure that the connection will
not slip off due to excessive weight or piping expansion/
contraction. Avoid low points and non-pitched piping
since dirt collects in low or level areas and may cause
stoppage and overflow.
Install condensate trap at each unit with the top of the trap
positioned below the unit condensate drain connection as
shown in Figure 6. Design the depth of the trap (water-
seal) based upon the amount of ESP capability of the
blower (where inches [51mm] of ESP capability requires
inches [51mm] of trap depth). As a general rule, 1-1/
inch [8mm] trap depth is the minimum.
Each unit must be installed with its own individual trap
and connection to the condensate line (main) or riser.
Provide a means to flush or blow out the condensate line.
DO NOT install units with a common trap and/or vent.
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CAUTION!
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Always vent the condensate line when dirt or air
can collect in the line or a long horizontal drain line
is required. Also vent when large units are working
against higher external static pressure than other units
connected to the same condensate main since this may
cause poor drainage for all units on the line. WHEN A
VENT IS INSTALLED IN THE DRAIN LINE, IT MUST BE
LOCATED AFTER THE TRAP IN THE DIRECTION OF
THE CONDENSATE FLOW.
DUCT SYSTEM INSTALLATION
