A fan coil unit (FCU) is a type of heating and cooling system used in residential and commercial buildings. It is an integral part of a HVAC (heating, ventilation, and air conditioning) system, and is used to provide temperature control and air circulation. FCUs are typically composed of a fan, a coil, and a filter. The fan is used to move air through the system, while the coil is used to heat or cool the air. The filter is used to remove dust and other particles from the air. FCUs are usually installed in the ceiling or wall of a room, and are connected to a central air conditioning system. They are relatively quiet and efficient, and are often used in places where space is limited. FCUs are also used in industrial applications, such as factories and warehouses, to help maintain a comfortable working environment.