Air handlers, also known as fan coils, are included on several different types of central HVAC systems. They are most often used with a heat pump system. Air handlers work by using a fan blower system positioned behind a built-in evaporator coil, electric heat element, or a combination of both. When the handler activates, the air is forced through the box and across the coil system, providing conditioned air (warm or cool) on the output side of the air handler and into the duct system of a home. These air handlers can be positioned in an upright position (upflow) or a downward position (downflow). They may also be installed in a horizontal position where the air flows from side to side through the unit, most common in crawl spaces or attics.
Here are some factors to consider if you need to replace your air handler:
Refrigerant Types in the Air Handler: The air handler and HVAC unit must use the same type of refrigerant! This is generally not an issue for most replacement units, since the indoor (air handler) and outdoor (condenser) units are usually replaced at the same time. If you are only changing the condenser, you MUST make sure the air handler can support the new unit. Condensers with an SEER of greater than 13 will probably not function with an air handler that is more than 3 to 4 years old.
Sizing of Air Handlers and Fan Coils: Indoor and outdoor units should have the same capacity. If you install a 3-ton heat pump condensing unit outside, your air handler MUST have a minimum of a 3-ton blower and coil. A system should NEVER have a smaller size indoor air handler than condenser. This will result in a frozen coil. You CAN install a slightly larger air handler than condenser, if your duct system is designed to support the higher airflow. A 3-ton condensing unit would work with a 3 to 4-ton air handler. In some cases, a slightly larger air handler can increase efficiency, but only if properly calibrated by a qualified HVAC professional.