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caring for your air conditioning equipment

Fan Coil Units: A Primer

by Amy Henry

If you are responsible for large scale commercial or residential building maintenance, then it is likely that you have come across fan coil units, commonly referred to as FCUs, as a heating and cooling solution. Fan coil units are relatively simple devices that help cool or heat fresh air that will be circulating through the living spaces of a structure. Fan coil units are commonly found in a wide variety of applications across commercial, residential, and industrial spaces. Fan coil units are a split system rather than a centralized system. Individual units may be installed to regulate the temperature of the air in smaller spaces or multiple units may be used to regulate temperature across a larger space.

Basic Operation

Although fan coil units can vary somewhat in design, the basic principles of operation are the same. In addition to the enclosure itself, all fan coil units consist of at least four basic elements:

  • A filter to remove particular matter from the fresh air supply
  • One or more fans to force air across the coils
  • Coils for heat exchange
  • A drain pan and plumbing to remove condensed water

Fan coils function as heat exchangers by drawing air in through the filter at the back of the unit and using fans to move that air across the heating and cooling coils. A drain pan is required to collect condensed water when the air passing through the unit is being cooled.

The internal design of fan coil units can differ depending on manufacturer and application. Some units feature a single heating and cooling coil, while others have two separate coils. These are generally known as two-pipe (one supply and one return) or four-pipe (two supply and two return) systems. The type of coils used can vary as well. Some units may simply pass warm or chilled water through their coil while others may use electrically heated coils and refrigerant.

In addition to conducting heat exchange with fresh air, most fan coil units are also designed to cool or warm some amount of interior air as well. This is accounted for in the design of unit's intake, which is generally not directly connected to the fresh air supply. Instead, the fresh air supply is allowed to mix freely with air from the space that is being regulated while some of the interior air is pulled back to the atmosphere outside of the building.


Fan coil units are a relatively simple and economical solution for temperature regulation. Although their split nature means that some extra maintenance is required, it also allows for independent temperature control across spaces. Individual fan control units can be turned on or off as needed as well, allowing the system to adjust to sudden increases in demand. Fan coil units are also highly space efficient since they need only be supplied with water via piping rather than warm or cold air through ducting.