An air handler is a unit that is used to move air within your home or office. Air handlers are specifically designed to work with an outdoor unit (a heat pump or air conditioner) . Air handlers are designed to circulate warmed or cooled air through traditional ducting throughout your home or office.
Usually, an air handler is a large metal box containing a blower, heating and/or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork that distributes the conditioned air through the home, and returns it to the air handler.
Air handlers can be paired with a heat pump in a split system or used with only an air conditioning unit. When paired with a heat pump in a split system the heat pump (outdoor unit) captures heat or cold from outside and moves the air inside to be distributed throughout your ducting system. When paired with only an air conditioner (outdoor unit) the air is captured from outside and is sent to the air handler, once the air is sent to the air handler the air is cooled through the evaporator coils and then distributed throughout the ducting system.