Hydronic Fan Coil Units

A hydronic fan coil unit is a compact terminal heating and cooling device that uses hot or chilled water — not refrigerant — to condition room air. A fan draws room air through a filter and across a water coil; the water heats or cools the air before returning it to the space. Hydronic fan coils connect to a boiler, air-to-water heat pump, or chiller as the water source, and each unit serves one zone independently.

Hot or chilled water is supplied from a central source — typically an air-to-water heat pump, boiler, or chiller — through insulated pipes to each fan coil unit. Inside the unit, a fan pulls room air through a filter and across the water coil. The air exits conditioned back into the room. Each fan coil operates independently, so different rooms can maintain different temperatures.

Yes. The same fan coil unit handles both heating and cooling depending on whether hot or chilled water is supplied. In a 2-pipe system, the entire loop switches between heating and cooling seasonally. In a 4-pipe system, each unit can heat or cool independently because separate hot and chilled water circuits run to every fan coil.

Yes — hydronic fan coil units are one of the primary distribution options for air-to-water heat pump systems. The heat pump produces hot water for heating and chilled water for cooling, circulating it to each fan coil. APOLLO fan coil units are designed for this application and connect directly to the heat pump's hydronic loop in both 2-pipe and 4-pipe configurations.

A 2-pipe system has one supply pipe and one return pipe shared by all fan coils. The system delivers either hot or chilled water at a time, switching seasonally. A 4-pipe system runs separate hot water and chilled water circuits to each unit, allowing individual zones to heat or cool simultaneously regardless of the season. 2-pipe systems are simpler and more affordable; 4-pipe systems offer greater flexibility for commercial or mixed-use buildings.

The choice depends on installation location, ceiling access, and how visible you want the unit to be. Wall-mounted units are the most straightforward. Floor units work well below windows in retrofit situations where ceiling access is limited. Ceiling cassettes suit open-plan rooms with central ceiling access. Concealed ducted units go inside a ceiling or wall cavity and are invisible after installation. For larger spaces or commercial applications, the commercial FCU or central AHU may be more appropriate.

Fan coil units need periodic filter cleaning or replacement every 1–3 months, clear airflow paths around supply grilles and return openings, and an annual inspection of the condensate drain pan and line when used for cooling. Check water connections and thermostat settings at the start of each season. They require significantly less maintenance than refrigerant-based split systems.

A fan coil unit is a compact, room-level terminal device that conditions one zone. An air handling unit (AHU) is a central system that conditions and distributes air for an entire building or a large section of it, typically through a duct network. MBTEK's APOLLO Central AHU is designed for whole-building hydronic air handling, while the FCU lineup covers individual room and zone applications.

No — and that is one of the defining advantages of hydronic fan coil units. Each unit conditions its own room or zone directly, drawing in room air, passing it across the water coil, and returning it to the space without a central duct network. The only runs required are a water supply line, a return line, and a low-voltage thermostat wire per unit. This makes hydronic fan coils a strong choice for retrofits where installing ductwork would be disruptive, and for new construction where a ductwork-free design is the goal.

The number depends on the heat pump's output capacity and the individual heating and cooling loads of each zone. A single APOLLO heat pump serves multiple zones through one shared water loop — each fan coil draws from that loop independently. The right answer for your project comes from a load calculation that accounts for room size, insulation, windows, climate, and required water temperature. MBTEK's system builder can help size your system.

Yes. When operating in cooling mode, fan coil units both lower air temperature and remove moisture. As warm room air passes across the chilled water coil, water vapor condenses on the coil surface and drains away — the same dehumidification principle used in conventional air conditioning. This is an important distinction from radiant cooling, which requires careful dew-point management to avoid condensation. Fan coil units do not have that limitation.

The key difference is what carries the energy inside your home. Refrigerant-based systems run refrigerant lines from an outdoor unit to each indoor head. With hydronic fan coils, a single outdoor heat pump produces hot or chilled water and distributes it through standard insulated water pipes — one heat pump serves every zone. There are no refrigerant lines inside the building and no outdoor compressor per room. The same water loop can also supply radiant floors, domestic hot water, or a pool, which a refrigerant-only system cannot do. For multi-zone projects, this typically means fewer outdoor units, less refrigerant, and a simpler installation overall.