A Fan Coil Unit (FCU) is a device used in HVAC systems to control the temperature of individual rooms or zones. It consists of a heat exchanger coil and a fan, which work together to either heat or cool air and circulate it into the space. FCUs rely on either a two-pipe or four-pipe system to receive hot or cold water from a central plant, allowing them to provide seasonal or simultaneous heating and cooling. Controlled by a thermostat, they offer localized temperature management, making them ideal for use in hotels, offices, and residential buildings.