Fan Coil Unit [FCU] vs Air Handling Unit [AHU]

So what is the difference between a fan coil unit and an air handling unit?

If we break down and compare the components of a fan coil unit and a simple 100% fresh air handling unit there is little difference to see between the two on the surface, as each would consist of the following:

• an air Intake/inlet
• an air filter
• a motor driving a fan
• a fan
• some form of coil [cooling/heating or both]
• pipework
• controls/control valves
• thermostat/temperature sensor
• condensation drip tray
• air discharge/supply

In this instance, the only real difference would be that the air handling unit operates by bringing in fresh air from the outside, whilst the FCU generally recirculates and conditions the air in the space it serves. They both move and condition air.

The below details a simple diagram of the basic components that they both have in common. 

Fan coil unit description

Fan coil units (FCU’s) are small single units that condition air and move it to the space via minimal ductwork. They can be used to manage small loads [KW], usually located in single rooms, recirculating the air.

They are quite versatile and inexpensive, having options to be installed in concealed in ceilings, exposed [out of ceiling], underfloor, or mounted vertically against a wall.

Air handling unit description

Air handling units [AHU’s] can be supplied as a complete single unit or in modules [components] that can be shipped to the site. If the unit is supplied in modules, during installation they will be bolted together to create a larger single boxed unit.

The air handling unit is designed, once installed and commissioned, to supply fully conditioned air [cooled or heated] to the multiple zones/spaces in the building allowing much larger loads [KW] to be managed than with the FCU.

The conditioned air that the unit creates is usually moved around the system via metal ductwork with the airflow being controlled by dampers and the temperature by valves [chilled/heating water].

FCU vs AHU Matrix

The units both on a drawing can look the same, but in actual fact, there are many differences that we have listed below:

Description	Fan Coil Unit [FCU]	Air Handling Unit [AHU]
Cost	Pretty reasonable	Can be very expensive
Size [physical]	Small	Large
Size/Capacity [KW]	around 12KW max	Over 100KW+
Used for	Directly serving single spaces/rooms	Serves multiple zones
Connected to	Flexible ducting to feeding grilles	Solid ducting serving multiple areas through building
Air Volume	Small	Large
Able to Cool	Yes	Yes
Able to Heat	Yes	Yes
Pipework configuration	2 pipe / 4 pipe	2 pipe / 4 pipe
Airflow	Small	Can be large
Noise	Low	Can be high
Controls	Simple	Can be complex
Variable Speed Drive [VSD]	Not usually	Yes should have
Condensate pipework	Required	Required
Manufacturing	Usually built as one complete unit	Usually manufactured in modules to allow easier shipping, movement around the site, and maintenance.
Delivery Period	3-6 weeks	6-12 weeks
Factory Testing	Usually not	Usually completed
Transportation	Less expensive as more can fit on the vehicle	Can be quite expensive depending on the size
Delivery and movement around the site	Quite easy [pallet truck]	Can require specialist handling equipment and resource
Type of building installed	Commercial buildings, Industrial buildings, Office buildings, Hotels, Schools, Residential	Commercial buildings, Industrial buildings, Office buildings, Hotels, Schools.
Installation location	Only internal spaces	Plant Room, Roof Top, External
Mounting	Slab [Exposed] Ceiling [Concealed] Floor [Verticle]	Usually, Plinth on the floor or can be a high level but require additional supports.
Access	Usually from the back or underneath	Usually from side
Maintenance	Easy	Easy, unless at high level then more complex due to size and weight of components
Maintenance Space	Not a lot required	Quite a large allowance to open doors and extract components/coils etc.
Onsite Installation	Simple	Simple, depending on space available
Operating costs	Minimal as long as commissioned and set up correctly	As long as commissioned and set up correctly can be not too bad depending upon the size of motor and unit etc.

So that’s it, a simple overview of the differences between an Air Handling Unit and a Fan Coil Unit.

If you want to read in more detail about Fan Coil Units then we have written an article ‘Fan Coil Units | What, Where & How‘.

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