There is one major drawback to this type of unit. Unlike central air and heating units where the fan is outside the home or place of business and cannot be seen or heard, these units can be loud because it is possible to hear the fan running. This noise occurs because the fan for the unit is sharing the same space and is not outside the building.
Fan coil units operate in the same sense as larger air conditioning and heating units through the process of heat transfer. When heating is necessary, hot water moves into a coil where heat is then collected and pushed into the air. When cooling is necessary, the same process occurs but instead of circulating hot water into the coil, cold air is used instead.
There are two main types of units: two pipe units and four pipe units. A two pipe unit has one supply pipe and one pipe for return. The former is used to supply the hot or cold water for the heat transfer, depending on what the fan coil unit is being used for.
The fan coil unit in its four pipe model has two pipes for supply and two for return. This type of unit is the most commonly used, especially in larger structures where spaces must be heated and or cooled simultaneously. The two supply pipes allow for the entry of both hot and cold water into the unit to allow this process to occur.