FCU (Fan Coil Unit)
A fan coil unit (FCU) is a terminal air-conditioning unit containing a fan and a water coil, installed in or near the room it serves and fed with chilled water (or hot water) from a central plant. It gives room-by-room control without ducting from a central AHU, and is the usual terminal in hotels, hospitals wards and cellular offices on chilled-water systems.
Why it matters on an MEPF project
FCUs are how a chilled-water plant reaches individual rooms without a duct network from an AHU: each room has its own fan, coil, filter and thermostat, so it can be off when unoccupied. That is the energy case; the design case is the fresh air, which an FCU does not bring in by itself and which has to come from a separate treated-fresh-air unit or a ducted supply.
The failures are quiet: condensate drains that block and drip, filters nobody cleans because the unit is above a ceiling, and units selected on nominal capacity at conditions the building never sees. Selection at the actual entering-water and air conditions, an accessible drain and filter, and a fresh-air path designed alongside are what make FCUs work.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| FCU | Room-level control; chilled-water plant; separate fresh air | Selection at design entering conditions |
| AHU + ducting | Zone-level control; filtration and fresh air in one unit | SMACNA-class ducting; TAB |
| VRF indoor unit | Room-level control on refrigerant, no chilled water | Manufacturer limits |
Common mistakes
- No treated fresh air — the FCU recirculates room air only.
- Drain trays without a fall or a trap; condensate drips through ceilings.
- Filters inaccessible above a fixed ceiling.
- Nominal capacity taken as delivered capacity at site conditions.
Related on this site
One of 68 working definitions in the MEPF & solar engineering glossary. The buying side of the same decisions is in the buyer's guides; the numbers are in the calculators.
Frequently asked
What is the difference between an FCU and an AHU?
Scale and function. An AHU is a large central unit that filters, conditions and often brings in fresh air, and distributes it through ducts to a zone. An FCU is a small unit serving one room from the chilled-water circuit, with its own fan and coil and no fresh-air intake of its own.
Standards referenced: NBC 2016 Part 8 · ISHRAE practice