Fan Coil Unit (FCU)

The Full Picture

A fan coil unit moves room air across a water coil. Chilled water makes it a cooler, hot water makes it a heater, and a thermostat controls the fan speed and a control valve. One university design guideline describes FCUs as relatively small, unducted, floor or ceiling mounted units used for cooling and/or heating the room in which they are located, and separates them from ducted blower coil units. They suit buildings with many small rooms that need individual control, where a central plant supplies the water.

The two-pipe versus four-pipe distinction changes what is counted. A two-pipe unit has one supply and one return connection on a single water loop, which carries either hot or chilled water depending on the season. A four-pipe unit has a chilled-water supply and return and a hot-water supply and return, so it can heat or cool at any time. Four-pipe units cost more and need more piping, valves and control hardware. The same university guideline calls for every unit to be individually scheduled and identified on the drawings, and it asks for a drain pan, a removable filter and insulated cold piping. Those features can show up as separate line items.

On the plans, FCUs are tagged on the mechanical floor plan, with piping runs shown to the unit. The equipment schedule lists the tag, type (floor, horizontal, recessed or concealed), CFM, cooling and heating capacity, coil connection size, motor data and the control arrangement. The takeoff unit is each (EA) by tag and size. The piping to each unit, valves, strainers, drain lines, power and thermostat are measured or counted separately by the mechanical and electrical trades.

Pricing slips include counting units by symbol while the schedule lists a different type, missing that some units are four-pipe and others two-pipe, and leaving out the drain or the control valve package. Another is the ceiling or wall opening: recessed units need a framed opening and access, which falls between the mechanical, framing and drywall scopes. Ventilation air is often supplied separately, and the guideline notes that units should not have an integral outside air connection where separate minimum ventilation air is provided so the ductwork for it is a different line.