Air Handler Basics

Air Handler

The air handler is a necessary component for an all-electric split system. Used specifically for ducted forced air systems that do not include a natural gas, propane or oil fired furnace. Air handlers are a standard piece of equipment for heat pumps and some split air conditioning systems.

The air handler takes fresh ambient air from outside to heat or cool the home. The air handler may also condition the air in other ways like cleaning, filtering, humidifying or dehumidifying. The blower motor then forces the air through the ductwork to the designated rooms. The air handler may have a fan to discharge the air back into the atmosphere but some units recirculate air from the building into the fresh air supply to save energy.

How Does It Work?

The air handler consists of a filter, an indoor coil, and the blower motor and is installed in the ductwork. Some air handlers may have additional components such as auxiliary heating strips and humidifiers to prevent the air from becoming overly dry in colder climates.

Air handlers come in a lot of different configurations and can adapt to meet the needs for the design of the building. An air handler can be installed horizontally in the attic or crawlspace or they can be installed vertically in a closet or basement. Ductwork will connect at both ends of the air handler regardless of the direction of installation.


Filtration is important in the air handler, all air handlers will include some type of filtration. Home units usually have a filter in the return air path. This filter can be a simple hepa filter, a UV filter or even an electrostatic filter. Filters prevent dirt and dust from entering the air handler. Without a filter, dust can build up inside the ductwork and mechanical equipment leading to poor air quality and equipment breakdowns. As the filters pick up debris the airflow becomes restricted and can cause a drop in the airflow pressure. Filters are usually conveniently located to allow homeowners to easily access the filter for cleaning or replacement.

There is a coil installed within the air handler which acts as a heat exchanger. The refrigerant travels through the line from the outdoor coil to an inlet on the interior coil within the air handler. Air moving across this coil will either be heated or cooled depending on the set point of the thermostat and which system is running, heating or cooling. Leaving the coil will be a suction line to return vapor to the outdoor coils and compressor. Inside the air handler is also a drain connection for condensation that may accumulate during cooling. A drip pan collects the condensation and drains it away from the air handler.

Next in line inside the air handler is a fan, the blower motor. Fans come from basic to multi-speed to fancy variable speed models but they all work to push the air through the ductwork out into the building. The fan pulls the air from the return, across the coils and out into the home. The thermostat will control when the fan turns on and off according to the set temperature or most thermostats also have a setting to leave the fan running continuously.

In an all-electric heat system like a heat pump, there will be a heat strip installed above the fan. This heat strip provides auxiliary heating or emergency heating when the system cannot produce enough heat on its own to reach the set temperature. Heating up much like the coils in your toaster, this heat strip is another place the air can source heat before entering the home. With a heat pump, this auxiliary heat strip will turn on when the system is in defrost mode to prevent cold air entering the building.