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An air handler, or air handling unit (AHU), is used to regulate and circulate air as part of a heating, ventilating, and air conditioning (HVAC) system. The air handler is usually located in a large metal box and contains a blower, heating and cooling elements, filters, and air ducts for taking in and releasing air.

Small air handlers, called terminal units, are for local use and may only include an air filter, a blower and a coil. Larger air handlers that condition outside air only are known as makeup air units. Air handlers designed for outdoor use, typically located on the roof of a commercial building, are known as rooftop units or as a packaged unit.

The air handler moves conditioned air throughout your building. If you have a forced air furnace, the air handler is the part that blows the warm air out. For an air conditioner, it circulates cooled air from the air conditioning unit.

There are several components to an air handler that must be maintained in order to have proper circulation of air flow.

The filtration system is possibly the most important part of the air handling unit. If the filtration system collapses, it will quickly contaminate and damage the rest of the system. Depending on the grade of the filtration system, filters will be arranged in two or more consecutive banks with both coarse grade panel filters and find grade bag filters to protect the system. Panel filters are cheaper, thus they are placed in front to protect the more expensive bag filters. As they collect dust and debris, they will begin to reduce the quality of the air flow. Monitoring the filter is important to keep the overall system running smoothly and efficiently, and can be done both visually, or with a pressure switch linked to an alarm on the building control system.

Depending on the type of system you have, your air handler may have heating and/or cooling elements attached to change the air temperature and the humidity level of the air flow. This process is performed through either direct or indirect heat exchanger coils. Direct heat exchangers include gas fired fuel burning heaters or a refrigeration evaporator placed directly in the air stream. Electric heaters or heat pumps can be used as well. Indirect coils use hot water or steam for heating, and chilled water for cooling. Copper or aluminum coils are used to aid in the heat transfer process.

In order to maintain a comfortable indoor air quality, air handlers have a process to introduce outside air into the system and exhaust to release air back out. A mixing chamber is used to control the ratio between the inside, outside and exhaust air.

Blowers may operate at a single speed, a variety of set speeds, or be driven by a variable drive that allows a wide range of air flow rates. Multiple blowers may be present, depending on the size of your commercial air handling unit. They are often augmented by fans in the return air duct pushing the air into the air handling unit. Fans have the possibility of becoming unbalanced, and will tend to wobble or vibrate. This vibration will greatly reduce circulation, compromise the efficiency, and create a noise within your system. This is often one of the first signs that maintenance is due.

Throughout the system, there are a variety of control components including temperature sensors, humidity sensors, switches, actuators, motors and controllers. Controls are necessary to regulate every aspect of the air handler.

Lots of components, lots of opportunity for potential problems. Do you remember the last time your HVAC system was tuned and had a regular maintenance check performed? Schedule yours today to keep your air handling unit, and your overall HVAC system running smooth all year through.