Air Handler Basics

An air handler is usually located in the garage, a closet, or in the attic (unless you
have a package unit then the air handler is incorporated in the system). It can be a part
of your furnace and houses the evaporator coils, the blower, and some controls. The air handler can be an upflow, downflow, or horizontal flow AHU (air handling unit). To determine
which one you have follow the return duct. The return duct should originate where you put the
filter and/or is the biggest register grill in the house. If the return ends in the bottom
of the unit it is an upflow air handler. If the return duct ends in the top of the unit it
is a downflow air handler. If the unit looks as if it is lying on it's side with the return
duct coming in one side the supply ducts going out the other it is a horizontal flow air
handler.

Knowing this information can help you find the filter if you have never changed
the filter in this unit. Some air handling units have the filter inside. If there is no filter
in the return register or grill then the filter is either in the return duct somewhere or
in the air handler itself. Filtering the air is not only important for the air quality in
your home but it is essential for the proper operation of the unit itself. The air must be
filtered before it reaches the coils or heat exchanger inside the air handler. If it is not
then there will be a build up over time of dust and debris that get sucked into the return.
This build up clogs off the evaporator coil and causes the heat exchanger to operate at
higher than normal temperatures. The unit becomes less and less efficient and will eventually
fail to cool or heat the home.