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 usually found together in Tempe. If you use a furnace, you likely shouldn’t need to spend time thinking about an air handler.

Air handlers are frequently paired with heat pumps and deliver airflow across your residence. Some models also have backup heating and cooling pieces to help the heat pump.

A furnace works in a different way by pushing hot air into your vents, which circulate it across your house. As furnaces have combustion chambers to produce warmth, they don't need some of the parts you'll see in a normal air handler.