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ll-Mounted Indoor Unit Engineering Manual
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Common Indoor Unit Drainage System
It is usual work practice to connect individual indoor unit drain pipes to one common indoor unit drainage system. The diameter of the com-
mon vertical drain pipe should be as large as necessary. The diameter of the horizontal pipe should be the same or larger than the vertical
drain pipe. To avoid property damage in the event of the primary drain becoming clogged, and to optimize drain system performance, it may
be prudent to install a secondary drain line. Design the drain system to plan for winter operation (condensate line may freeze up if conden-
sate does not properly drain away). Drain all generated condensate from the external condensate pan to an appropriate area. Install a trap
in the condensate lines as near to the indoor unit coil as possible. To prevent overflow, the outlet of each trap should be positioned below its
connection to the condensate pan. All traps should be primed, insulated, and leak tested if located above an inhabited space.
Figure 63: Example of a Common Indoor Unit Drainage System.
APPLICATION GUIDELINES
General Drain Piping Information
Common horizontal drain pipe
1/50 to 1/100 Slope
27-1/2 in.
(Maximum pump
lift distance
[depends on indoor
unit type]).
Include trap
at the end.
45° to 60° Angle
Position the vent
down to prevent
debris from entering
the system
45° to 60° Angle
45° to 60° Angle
45° to 60° angle for protection against overflow
Common
vertical
drain pipe
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