Fan coil units explained

What a fan coil unit is

A fan coil unit is a compact indoor unit containing a heat-exchange coil and a quiet fan. Water from the heat pump flows through the coil; the fan draws room air across it. In winter the coil is warm and the unit heats; in summer the coil is chilled and the unit cools. A built-in tray collects any condensation and drains it away.

Because it actively moves air across the coil — rather than relying on natural convection from a hot surface — a fan coil can transfer far more heat for its size than a radiator, in either direction.

Why a fan coil can cool when a radiator can't

A radiator only works in one direction. It heats well because hot air rises and circulates on its own. In cooling, there is no such natural help — cold air sinks and stays put — so a cold radiator barely affects room temperature. Worse, its cold surface would collect condensation and drip onto the floor.

A fan coil solves both problems. The fan forces air across the chilled coil so heat is actually removed from the room, and the condensate tray and drain deal with the moisture that cooling inevitably produces.

The main types

Fan coil units come in several formats so they can suit different rooms:

• Wall-mounted — mounted high on a wall, similar in position to an air-conditioning indoor unit.
• Low-level / floor — sit at skirting height, often where a radiator used to be.
• Ceiling or concealed — built into a ceiling or bulkhead, with only a discreet grille on show.

Modern units with EC/DC inverter fans are designed to run quietly. The practical advice is to choose a slightly larger unit and run it slowly, rather than a small one forced to run fast.

Fan coils heat as well as cool

A fan coil is not a cooling-only device. The same unit delivers low-temperature heating from your heat pump in winter, so a fan coil circuit can be a year-round emitter — not a separate system that sits idle for half the year.

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