How Does an Air Handler Work?
Understanding how your HVAC system works can help you improve your comfort, save on energy, and make HVAC replacement easier when the time comes.
By Anne Fonda
What is an air handler?
Briefly, an air handler is an indoor HVAC unit that circulates heated or cooled air throughout your home. It’s part of a matched system of heat pump + air handler or AC unit + air handler. Systems are matched for capacity and energy efficiency.
An HVAC air handler contains the evaporator coil and a blower fan, with the additional possibility of auxiliary heat electric heat strips. The cabinet may also house a filter rack and UV lights to prevent mold in humid climates.
Some people may refer to the air handler as an air handler unit or air handling unit. Whatever you call it, it’s an integral part of your heating and cooling system.
How an air handler works: circulating air
An air handler itself doesn’t heat or cool your home. Instead, the blower fan blows air over the evaporator coil to add or remove heat from the air in the heat exchange process. The heated or cooled air is then blown into your ductwork and into your home via supply registers.
The air is pulled back into the system through the return air vents. The return air ducts bring the air back to the air handler, where air passes through an air filter or whole-house air cleaner before it enters the air handler again. The air filtration system filters out dust, pollen, and other particulates.
Difference between an air handler and a furnace
On the outside, an air handler looks similar to a furnace. The inner workings are encased in a large metal cabinet located in your basement, attic, crawl space, or utility closet. Inside the units, things are very different.
Air handler
Inside the air handler cabinet, you’ll see the evaporator coil, control board, blower fan, and other components. When paired with an air conditioner, the AC air handler circulates cooled air throughout your home.
When paired with a heat pump, the air handler circulates cool air in the warmer months and heated air in the colder months. If you hit a sudden cold snap, optional auxiliary heat strips inside the air handler can activate to help keep you warm.
Furnace
Inside the cabinet, a furnace has ignitors, burners, and a heat exchanger, as well as a control board and blower fan. In the colder months, the furnace burns a fossil fuel (natural gas, oil, or propane), and a blower fan forces the warm air into the ductwork to heat your home. In the summer, the furnace acts as an air handler to circulate the cooled air from the air conditioner and the paired indoor coil.
Maintaining your air handler
Regular air handler maintenance will help your system function more efficiently and can prolong the life of the unit. For optimal comfort, schedule HVAC maintenance in the spring and fall. The HVAC technician will check both the indoor air handler and the outdoor AC unit or heat pump. A maintenance visit can include:
- Checking the operation
- Checking and cleaning the blower fan and blower motor
- Checking and cleaning the evaporator coil
- Lubricating all moving parts
- Tightening loose parts or electrical connections
- Doing similar maintenance checks on the outdoor unit
You can help maintain your air handler as well. Change the air filter every 30-90 days, depending on the quality of the filter. You’ll want to check it more often if you have pets or allergies. Check our HVAC air filter maintenance guide for some tips.
Trane air handlers
Trane air handlers are available with variable-speed or single-speed fan blower motors. Variable-speed models are known for soft starts, high humidity controls, variable airflow capacity, and the enhanced comfort mode, the Comfort-R™ airflow system.
Variable speed units generally offer higher energy efficiency and precise airflow, consistent temperature, and better control of humidity levels. Read our blog on Trane’s Best Air Handlers to get a feel for the superior technology and materials we use to provide energy-efficient, durable air handlers.
In certain combinations, an air handler paired with a heat pump may be eligible for a $2,000 tax credit and additional heat pump rebates, depending on where you live and your income level. More energy-efficient systems will help you lower your energy bills. The tax credit is only available for qualifying systems installed before December 31, 2025.
Work with the HVAC sustainability experts
If it’s time for HVAC replacement or HVAC repair, reach out to your local Trane dealer for help. They have the expertise you need to help you choose a new HVAC system for your home or extend the life of the one you have with HVAC maintenance and service.
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism.
When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Erica Harrison, Product Manager, Air Handlers
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