Proper air circulation is essential to your home’s heating, ventilation and cooling (HVAC) system. While some residential HVAC systems simply use the furnace’s blower to circulate air, others use an air handling unit (AHU). AHUs, for instance, are commonly found in heat exchanger setups. If your home has a heat exchanger – as opposed to an air conditioning system and furnace setup – it probably has an AHU. What is an AHU exactly?

The Basics of an AHU

Also known simply as an air handler, an AHU is a large box that contains several essential HVAC parts It’s designed to circulate or “handle” the air in your home. When running your HVAC system, it will pull the unconditioned air from inside your home so that it can be conditioned. The AHU contains a blower motor and fan. During use, it will suck in unconditioned air through the return vents.

Most AHUs contain the following parts:

·         Air filter

·         Evaporator coil

·         Blower motor

·         Fan

It’s important to note that some AHUs may contain additional parts. Whole-house humidifiers, for example, can be installed in them. If your home suffers from dry air, you may install a humidifier in the ACU. Regardless, most ACUs consist of the aforementioned parts, all of which are found within the ACU’s box.

How the ACU Works

The ACU’s primary purpose is to circulate air for conditioning purposes. HVAC systems, including those with a heat pump, don’t actually produce warm or hot air. Rather, they act like a heat exchanger by adding or removing heat to your home’s existing air.

The blower motor and fan will create a suction that pulls in unconditioned air. Upon entering the ACU, the unconditioned air will pass over the evaporator coil. If you’re using your HVAC system to cool your home, the unconditioned air will be cooled during this process. The evaporator coil consists of several refrigerant-filled tubes. The refrigerant will absorb heat from the unconditioned air as it passes over the evaporator coil.

ACUs contain the air filter as well. All HVAC systems have an air filter. In a heat pump setup, the air filter is typically found in the ACU. In a traditional air conditioning system and furnace setup, the air filter is typically found in the furnace. Both types of HVAC systems use an air filter to purify the air. Air must pass through the filter before being conditioned. If it’s located in the ACU, unconditioned air will first enter the return vents, after which it will pass through the filter before passing over the evaporator coil.