Attic Installation Horizontal Flow Air Handler – Attic Air Handler – AHUThis is a horizontal flow air handler installed in the attic. Notice the drain pan under the air handling unit to catch condensation if the primary pan were to overflow. This is the secondary condensation pan which is installed under the air handler to save a ceiling. Also slightly visible is a float switch which offers triple protection against flooding in an attic if the primary drain were to plug up. The primary and secondary drains coming from the air handler also drain into condensation pumps. These pumps have floats inside them and a reservoir.

Attic Installation Horizontal Flow Air Handler | HVAC Airflow

When the reservoir reaches a certain height the float switch rises and turns on the motor and the pump which pumps the condensation out of the attic and usually outside but these drains can also terminate in a sanitary drain. If the condensation drain is piped directly to the sanitary drain it is important that properly pipe methods including traps be used to prevent sewer gases from back feeding into the condensation drains and eventually into the air handler and air stream which provides air to the structure.

The important part of this attic installation is that the air handler has plenty of drains and a safety cutoff to ensure that the air handler turns off before the secondary drain pan overflows into the attic.


Horizontal flow air handlers can be configured in left to right or right to left configurations upon installation. This makes it helpful to retrofit a new AHU to existing ductwork as necessary.  It is simply a matter for the installer to flip the evaporator coil so that the condensation pan is under the coil to catch the condensation.

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Attic Installation Horizontal Flow Air Handler | HVAC Airflow

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