https://www.serviceexperts.com/faq/what-is-the-difference-between-an-air-handler-and-furnace

Air handlers and furnaces aren't typically installed in the same home in North America. If you have a furnace, you most likely won’t need to think about an air handler. Air handlers are frequently paired with heat pumps and manage airflow across your residence. Some systems also provide extra heating and cooling pieces to support the heat pump. A furnace heats in a different manner by pushing heated air into your vents, which send it across your residence. Since furnaces depend on combustion chambers to produce heated air, they don't have some of the parts you'll see in a standard air handler.

What is the Difference Between an Air Handler and Furnace?

Air handlers and furnaces aren't typically found together in Rochester. If you have a furnace, you likely shouldn’t need to consider an air handler.

Air handlers are typically used with heat pumps and deliver airflow around your home. Some systems also provide secondary heating and cooling parts to assist the heat pump.

A furnace works in a different way by blowing warm air into your vents, which circulate it throughout your residence. As furnaces use combustion chambers to make heated air, they don't use some of the pieces you'll spot in a normal air handler.