Chilled beams or fan coil units for an office?
Updated 23 October 2026 · SEO Dons Editorial
How does a chilled beam differ from a fan coil unit?
Both are water-fed terminal units, but they cool in different ways. A fan coil unit pulls room air across a coil with a fan and, where it is meant to dehumidify, needs condensate drainage (see the fan coil units guide). A chilled beam has no fan of its own. CIBSE Journal explains that it exchanges sensible heat between room air and a cool coil, and that any dehumidification in the space must be done by an associated central air supply.
Beams come in two forms. Passive beams rely on natural convection currents in the room, driven by denser cool air being drawn downwards by gravity. Active beams are supplied with ducted primary air from a central system, generally the same air that meets the ventilation requirement, and that air induces room air through the coil. The air handling unit guide covers the central side.
Why do chilled beams need warmer water and tight humidity control?
The surface of a beam must not fall below the dew point of the surrounding air, or condensation is likely. So beams run on moderately high chilled water, 14 to 18 °C according to CIBSE Journal, while the central air handling unit typically needs water at about 6 °C to dehumidify. The commercial chillers page covers the plant side. One chiller can serve both by mixing, but separate chillers can use less energy, and CIBSE says the beam chiller can work to a 14 °C setpoint, which significantly increases its performance.
Control is the other half. CIBSE describes sensors on the cold-water supply that close water valves when moisture levels rise, and notes that dry cooling relies on enough air supply to manage latent loads. The Energy Technology List (ETL) says the same for active beams: they must be designed to operate above the dew point, and dehumidifying the primary air and controlling the water temperature are important to prevent condensation. A fan coil is built to condense and drain, so it does not depend on dew-point control in the same way.
How much cooling does each deliver?
Beam capacity is published per metre or per module, so a floor-area figure has to be worked out room by room, and none of the sources used here publishes one. The ETL sets minimum specific waterside cooling capacities in watts per metre per kelvin. Using the 8 K minimum temperature difference in the same table, simple multiplication (not a figure the ETL publishes) gives about 200 W per metre for a two-way beam up to 300 mm wide and 360 W per metre for a two-way beam between 300 and 600 mm wide.
| Example | Published figure |
|---|---|
| ETL minimum, two-way linear active beam up to 300 mm wide | 25.0 W/mK, about 200 W/m at 8 K |
| ETL minimum, two-way linear active beam over 300 to 600 mm wide | 45.0 W/mK, about 360 W/m at 8 K |
| Swegon FRB, exposed passive beam, 1.2 to 3.9 m long | 252 W/m at a 10 K difference |
| Swegon Parasol four-way module, 600 and 1200 mm sizes | Up to 2,055 W total cooling, primary air up to 85 l/s |
| Daikin FWF-D cassette fan coil, 600 x 600 mm module | 1.3 to 5.1 kW |
| Daikin FWQ-A concealed fan coil | 2.1 to 11.5 kW |
Read it with care. The figures use different rating conditions, "up to" values are maxima, and a fan coil's declared capacity includes both sensible and latent cooling, whereas a beam leaves moisture removal to the air system. On headline numbers a 600 mm cassette lists a higher top figure than a beam module of similar footprint, but it brings a fan, a filter and a condensate drain with it.
Which is quieter and easier to maintain?
A beam has no fan, so it adds no fan noise and no fan to service in the room. The ETL defines active beams as having no integral fan, and CIBSE says they typically omit filters and drainage systems, which reduces service and maintenance needs. A fan coil carries all of those items: CIBSE lists filters, condensate drip trays and pumps, and control elements that need a carefully considered maintenance procedure.
Beams are not silent, and they are not maintenance-light everywhere. CIBSE warns that boosting active-beam airflow means raising duct pressure, which can generate increased noise, and the work moves to the central plant, ductwork and humidity controls rather than disappearing.
What about ceiling space, layout changes and energy?
Space. Multi-service beams integrate ducts, lighting, cabling and sensors into the casing and, fixed to the structural soffit, can negate the need for a dedicated ceiling void, according to CIBSE Journal. Fan coils sit above or in the ceiling and need service access planned at design stage.
Layout changes. CIBSE says unitising heating and cooling simplifies zoning, local control and later reorganisation of room layouts, and that a fan coil system is surpassed only by more expensive and less flexible systems such as chilled beams and ceilings. If you are considering beams, ask the supplier how zones and primary air would be re-divided when partitions move.
Energy. The ETL encourages active beams for their relatively high chilled water temperatures and small volumes of outdoor ventilation air. Against that, CIBSE notes beams use a 2 K to 3 K water temperature difference against 5 K to 6 K for other distributed units, so pumping energy is higher. A REHVA/ASHRAE design guide, quoted in CIBSE Journal, concludes beam systems may offer significant savings in operating costs, namely in energy and maintenance. The saving depends on the building, so ask for it to be calculated for yours.
Which suits an office?
| If the office... | It leans towards |
|---|---|
| Has a mechanical ventilation system that will supply all fresh air, and you want no fans, filters or drains in the ceiling | Chilled beams |
| Expects frequent partition and tenancy changes | Fan coil units |
| Has spaces where humidity can spike, such as meeting rooms | Fan coil units, or beams with dew-point control and enough primary air |
| Can run its chiller at 14 to 18 °C for the terminals | Chilled beams |
| Will heat from a heat pump | Either: beams on hot water at 32 to 45 °C, or fan coils with heat pump-ready coils |
Either way the terminals depend on the central plant. The commercial chillers page explains how chilled water systems are specified, and the 2-pipe versus 4-pipe guide covers the fan coil heating side. For offices generally, see the office air conditioning page, and you can send an enquiry through the site's form if you want a design compared for your building.
Sources
Regulations and guidance are revised, so confirm the current text before relying on a figure. Manufacturer figures are examples from named products, not a ranking.
- Module 233: Variable geometry chilled beams for efficient variable air volume (VAV) systems, CIBSE Journal, posted May 2024; checked 22 October 2026.
- Module 65: Applying chilled beams to reduce building total carbon footprint, CIBSE Journal, posted June 2014; checked 22 October 2026.
- Module 83: Integrating centralised hybrid heat pumps with independent room units for energy-efficient concurrent heating and cooling, CIBSE Journal, posted October 2015; checked 22 October 2026.
- Module 101: The evolution of fan coils for efficient conditioning of room air, CIBSE Journal, posted September 2016; checked 22 October 2026.
- Active Chilled Beams, Energy Technology List, UK Government; checked 22 October 2026.
- Heating, ventilation and air-conditioning (HVAC) equipment, Energy Technology List, UK Government; checked 22 October 2026.
- Commission Regulation (EU) 2016/2281, annex II, legislation.gov.uk, revised 09/01/2017; checked 22 October 2026.
- FRB passive chilled beam, Swegon UK, manufacturer's own page; checked 22 October 2026.
- Parasol comfort module, Swegon UK, manufacturer's own page; checked 22 October 2026.
- FWF-D cassette fan coil, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- FWQ-A concealed fan coil, Daikin Applied UK, manufacturer's own page; checked 22 October 2026.
- Module 252: Design considerations for fan coil units with low-temperature heat sources, CIBSE Journal, posted August 2025; checked 22 October 2026.
Common questions
Can chilled beams heat as well as cool?
Active beams can. CIBSE Journal says they may be used as heating sources with low-temperature hot water, typically below 50 °C, alongside warm primary air.
Do chilled beams always need an air handling unit?
Active beams are supplied with ducted primary air from a central system. Passive beams move air by convection, but CIBSE says any dehumidification must still come from an associated central air supply.
Are chilled beams in the Energy Technology List?
Active chilled beams are. The ETL covers them in its HVAC category and sets performance thresholds and design conditions, including operation above the dew point and no integral fan.
What stops a chilled beam dripping?
Dew-point or humidity sensors on the cold-water supply can close the water valves when moisture rises. CIBSE adds that some methods now adjust the supply water temperature to room conditions instead.
Related guides
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