How to choose a fan coil – capacity, mounting type and number of pipes
How to choose a fan coil – performance, type of installation and number of pipes
A fan coil is a device that at first glance looks simple – air passes through a water heat exchanger and a fan distributes it into the space. In reality, however, choosing the right fan coil for a specific application is much more complex than it seems. You are not only deciding on the performance, but also on the type of installation, the number of pipes in the hydraulic connection, control, accessories and the mutual compatibility of all components. From practice, I know that underestimating any of these factors is the most common reason for later unsatisfactory comfort – the fan coil "does not cool enough", "blows too much air", "drips condensate on the floor" or "does not reach the desired room temperature in the morning frost".
This article will guide you through the entire selection process step by step, with real numbers, typical scenarios from practice and a clear explanation of technical terms, so you know exactly what you are ordering and why.
What is a fan coil and how it works
A fan coil (fan-coil unit, FCU) is a local air conditioning unit that uses water as a heat transfer medium. Unlike split air conditioners, where refrigerant flows directly into the unit in the room, a fan coil uses a central source – a chiller (water cooler), heat pump or boiler. Cooled or heated water circulates through pipes to the fan coils, which "transfer" it to the air in the room.
The basic principle of operation is as follows: the fan draws air from the room (or from the outside in the case of fresh air connection), forces it through the fins of the heat exchanger, where the air is cooled or heated, and then releases the modified air back into the space. During cooling, condensation of air humidity occurs on the cold fins – condensate must be drained, which is one of the key installation requirements.
Fan coils are used in hotels, offices, apartment buildings, clinics, shops, showrooms – in short, everywhere there is a central source of heat or cooling and where it is desirable to locally regulate the climate in each room separately. In recent years, their popularity is also growing in single-family homes in combination with a heat pump.
First step: correct calculation of the required performance
The performance of a fan coil is a fundamental parameter – that is why we dedicate a separate article to it in this Knowledge Center: What fan coil capacity do I need for my room. Here we summarize the key principles so that we can correctly filter models when selecting.
The performance of a fan coil is usually given in kilowatts (kW) and is defined for specific operating conditions. The standard EN 16430 defines standard conditions for cooling as: inlet water temperature 7 °C / outlet 12 °C, room air temperature 27 °C (dry bulb) / 19 °C (wet bulb). For heating it is typically inlet water 50 °C / outlet 40 °C at an air temperature of 20 °C.
From practice, I would like to point out an important point: if you are working with a heat pump, the water temperature during heating is much lower (e.g. 35 °C / 30 °C). Under such conditions, the heating performance of the fan coil may drop to 50–60 % of the catalog value. Always check, therefore, what performance the device will provide at your specific water parameters, not just at the standard conditions from the table.
As a rough estimate: for a well-insulated apartment in a new building, calculate about 50–70 W/m² for cooling and 60–80 W/m² for heating. For older buildings without insulation, the need may be 100–120 W/m² or more. A 25 m² room in a new building therefore needs a fan coil with a cooling capacity of at least 1.25–1.75 kW, ideally with a reserve.
Types of fan coil installation – basic classification
The second key decision is the method of installation. Fan coils are divided into several basic groups according to their location and orientation, each of which has its own specific advantages, disadvantages and requirements for construction execution.
Ceiling-mounted (cassette) fan coils
They are mounted in the ceiling soffit, with only a decorative grid visible at the level of the ceiling. Air is distributed in several directions (2-way, 4-way cassettes). The advantage is even air distribution in the room and almost invisible installation. The disadvantage is the need for space above the soffit (usually min. 250–350 mm) and access for service.
Wall-mounted (ceiling-mounted) fan coils
They are mounted on the wall or directly on the ceiling (horizontal version). They are visible, but aesthetically solved. Suitable for renovations where there is no soffit. Air is blown horizontally along the ceiling or down the wall. A more detailed comparison can be found in the article Recessed vs. wall-mounted fan coils – which solution is suitable for my project.
Floor-mounted (console) fan coils
They are placed at the floor level, under the window sill – similar to classic radiators. Air circulates from the floor upwards. The advantage is simple installation without the need for a soffit or special construction interventions, the disadvantage is a smaller air reach and less even distribution in the room.
Built-in (ducted) fancoils
They are hidden in the ceiling or in an installation cabinet, and only the air outlets are visible in the room. They allow air distribution to multiple rooms from one unit. These include, for example, models from the IVAR SLI range, where an intake set for IVAR.SLI DC 400 or an intake grid for IVAR.SLI DC 600 is available – these components solve the issue of air intake into the concealed unit and are part of the complete installation.
Key parameter: number of pipes (two-pipe vs. four-pipe connection)
This is a point where many investors and sometimes even designers make a mistake that is hard to correct after the building is completed. The number of pipes determines whether you can cool and heat simultaneously in different rooms or not.
Two-pipe connection (2-pipe)
In a two-pipe system, one supply and one return pipe lead to the fancoil. The system can be set either for cooling or for heating – but not both at the same time. Switching is done centrally for the entire system (e.g., in spring and autumn). This is a more cost-effective solution in terms of piping costs and is sufficient for most applications in residential buildings and offices, where cooling is used in one period and heating in another.
Disadvantage: during the transitional season (spring, autumn), you may encounter a situation where one side of the building is hot and needs cooling, while the other is cold and needs heating – and a two-pipe system cannot handle this simultaneously.
Four-pipe connection (4-pipe)
Two separate circuits lead to the fancoil – one for cold water (cooling) and one for hot water (heating). The fancoil can thus switch individually between cooling and heating, regardless of what the neighboring fancoil is doing. This is an ideal solution for hotels (each room regulates itself), hospitals, buildings with different façade orientations, and anywhere simultaneous operation is required.
The cost of piping is higher (twice as much piping), and it also requires a fancoil equipped with two separate heat exchangers or one combined one. A detailed technical explanation of both connections can be found in the article Two-pipe and four-pipe fancoil connections – the difference and when to use which.
Differences between constant and DC INVERTER fan speed control
The performance of a fan coil depends not only on the heat exchanger but also on the fan speed. Traditional fan coils had 3-speed switching (low, medium, high). Modern units with DC INVERTER technology allow smooth speed control in a range, e.g., 30–100 %, which brings several advantages:
- Lower noise – a fan coil running at 40–60 % speed is significantly quieter than one at full power; this is crucial in a bedroom
- Lower energy consumption – the fan is one of the biggest consumers in an FCU; reducing speed to 50 % can reduce motor consumption by 70–80 %
- More precise temperature control – without jumps, smoothly
- Longer service life – fewer frequent switching cycles
For standard office spaces, 3-speed control is sufficient. For bedrooms, children's rooms, and exclusive applications, I recommend DC INVERTER. Available is also control for IVAR.SL, SLS – built-in, 4-speed, 230V, which provides comfort of four-speed control for fan coils of this series. The extended topic of control – from a simple switch through thermostat to BMS – is covered in the article Fan coil control – from a simple switch to smooth DC INVERTER control.
Installation requirements and dimensions – what to consider before ordering
Choosing a fan coil without considering installation conditions leads to problems during installation. Each type of mounting has specific requirements for the building structure:
Recessed ceiling fan coil
The minimum height of the ceiling cavity is usually 200–280 mm for compact models and up to 350–450 mm for more powerful units. In addition, it is necessary to ensure an access opening for service (minimum 600×600 mm). The condensate drain must be sloped (min. 1.5 %) or equipped with a condensate pump. For perfect concealment of the unit into the structure, special installation boxes for air conditioners and fan coils are used, which allow clean and tight embedding into the ceiling or drywall partition.
Floor/parapet fan coil
The space under the parapet must allow air intake from below or in front. The minimum depth of the installation niche is usually 120–200 mm, the height according to the model. Accessibility for filter cleaning (without dismantling the entire unit) is important.
Wall-mounted fan coil
Mounting on load-bearing brackets. It is necessary to solve the pipe routing (in grooves, channels or embedded installation). Condensate pipe from the wall to the drain. Electrical supply near the unit.
Exact dimensions and installation requirements for the specific models of the IVAR SL, SLI and SLS series can be found in the article Dimensions and installation requirements of IVAR SL, SLI and SLS fan coils, where there are also drawing materials for designers.
Air quality, filtration and hygiene
The fan coil circulates air through the filter and heat exchanger, which directly affects the indoor environment quality. Standard equipment is a simple panel filter of class G2–G3 (captures larger dust particles). For allergy sufferers and spaces with higher hygiene requirements (hospitals, clinics, neonatal units), a supplementary filter of higher class or UV-C disinfection is recommended.
An interesting solution is UVC lamp for IVAR.SL, SLI 400 – L=475 mm fan coils, which is mounted directly into the fan coil and disinfects the air during its passage through the radiation. UV-C rays effectively destroy bacteria, viruses and mold on the heat exchanger fins, which is important especially in the summer operating period, when cold and moist fins are an ideal environment for microorganism growth.
Do not forget: the filter must be regularly cleaned – usually every 4–8 weeks during normal operation, more frequently in dusty environments. A neglected filter dramatically reduces air flow, device performance and can lead to freezing of the heat exchanger during cooling. The entire issue of cleaning and maintenance is covered in the article Cleaning and maintenance of fan coils – filters, UVC lamps and regular service.
How to proceed with selection – step by step
Based on experience from dozens of implementations – from apartment buildings through single-family homes to commercial buildings – I have compiled a practical procedure that minimizes the risk of incorrect selection:
Step 1 – Define the source of heat/cooling: What kind of chiller or boiler do you have? What is the water temperature for cooling and heating? This directly affects the actual (not catalog) performance of the fan coil.
Step 2 – Calculate the thermal load: For each room separately – area, orientation, glazing, thermal insulation of the building envelope, internal heat sources (people, equipment). Without this step, you are just guessing.
Step 3 – Choose the type of mounting: Ceiling? Where is the condensate drain? How much space is available? Is it a new building or a renovation?
Step 4 – Decide on the number of pipes: Is a two-pipe system sufficient, or do you need simultaneous heating and cooling in different rooms?
Step 5 – Choose control: Simple thermostat? Intelligent control with BACnet/Modbus for BMS system? Smooth DC control for night silent mode?
Step 6 – Check accessories: Does the fan coil have everything it needs – filter, condensate tank, condensate pump (if no slope), shut-off valve, check valve, air vent?
Step 7 – Verify installation dimensions: Does the unit really fit into the planned space including service access?
The procedure and details of installation can be found in the article Installation of a fan coil – procedure, connection and commissioning.
Typical scenarios from practice
Scenario 1 – Apartment building, 12 apartments: Developer plans to install fan coils in each apartment instead of radiators, the heat source is an air-to-water heat pump. Heating water temperature 35/30 °C, cooling 7/12 °C. Used two-pipe connection with central seasonal switching. Floor-mounted fan coils in each living room, electric heating in bathrooms. The performance at heating with 35 °C inlet was only 65 % of the catalog value – so more powerful models had to be selected. Result: satisfied tenants, energy class A.
Scenario 2 – Boutique hotel, 30 rooms: Each room must have an individual climate independent of the others. Solution: four-pipe connection, cassette fan coils in the ceiling, integration into the hotel control system via BACnet. Complication: in some rooms the ceiling height was only 220 mm – ultra-low models had to be used and in one case the pipe route had to be moved.
Scenario 3 – Family house, renovation: The owner wants to replace radiators with fan coils, the heat source is an existing gas boiler. Water temperature 55/45 °C. Floor-mounted (parapet) fan coils, two-pipe. In summer the boiler is turned off and a chiller is not planned – the system will be used only for heating. Simple and economical choice. Warning: without a cooling source, the fan coil does not cool – it only blows air!
Scenario 4 – Offices, open space 400 m²: Ceiling height 350 mm, large south-facing glazing. Need for cooling primarily. Four-way cassette fan coils, two-pipe chiller system. Challenge: in winter heating was insufficient due to low water temperature (chiller has reverse mode, but only up to 45 °C inlet). Solution: additional electric heating in fan coils for extremely cold mornings.
Most common mistakes when selecting a fan coil
- Undersizing the capacity – the most common problem; do not rely only on room area, always consider heat gains through glazing as well
- Not considering the actual water temperature – the catalog shows performance under standard conditions, with a heat pump at 35 °C the performance is significantly lower
- Forgotten condensate – condensate is formed during cooling and must have a place to drain; missing slope or pump = dripping on ceiling/floor
- Wrong choice of connection – investment in a two-pipe system in a hotel means either heating or cooling for the entire building; this will not satisfy the guests
- Unsolved control – a fan coil without a thermostat only heats/cool at full capacity; temperature will fluctuate and energy consumption will be unnecessarily high
- Ignoring noise – cheap fan coils with asynchronous motors can be disturbing at night; always check the noise level (dBA) at the lowest speed
Overview of selection criteria – table
| Parameter | What to look for | Typical values |
|---|---|---|
| Cooling capacity | kW at 7/12 °C, 27/19 °C | 0.5–10 kW (typical FCU) |
| Heating capacity | kW at 50/40 °C or 35/30 °C | 0.8–15 kW |
| Air flow | m³/h at max speed | 150–2500 m³/h |
| Noise level | dBA at low speed | 22–45 dBA (lower = quieter) |
| Water connection | water flow in l/h, DN connection | DN 15–25 |
| Number of pipes | 2-pipe or 4-pipe | according to the system |
| Control | on/off, 3-speed, DC inverter | according to requirements |
| Dimensions (h×w×d) | mm, including installation space | very variable |
Accessories without which the fan coil cannot do without
The fan coil unit itself is only part of the overall solution. For reliable and comfortable operation you also need:
- Thermostat / controller – either built-in (for example 4-speed control 230V for IVAR.SL and SLS), or external room thermostat
- Closing and balancing valve – for proper hydraulic balancing of the system
- Air vent – essential for each fan coil; air in the heat exchanger prevents proper water circulation
- Condensate pump – if a slope drain for condensate is not available
- Filtration accessories – suction kits, grilles (for example inlet grille for IVAR.SLI DC 600) for built-in solutions
- Installation box – for clean integration into the building (installation box for air conditioners and fan coils)
- UV-C lamp – for hygienically demanding environments or allergy sufferers
Common questions (FAQ)
Can I use a fan coil only for heating, without cooling?
Yes, a fan coil is a full-fledged heating element. Many new buildings combine a heat pump and fan coils precisely for heating, while cooling in summer is a pleasant bonus. If you plan to cool in the future, ensure the hydraulic piping is already in place today – additional pipe installation is expensive. It is enough to have the piping blinded and later connect the chiller.
What is the difference between a fan coil and a split air conditioning system?
A split air conditioning system works with a refrigerant that circulates between the outdoor and indoor units. A fan coil works with water – it is connected to a central hydraulic system. Fan coils are suitable for central sources (chiller, heat pump, boiler), where one outdoor unit supplies dozens of fan coils. Splits are simpler for a single room or a small building.
How noisy are fan coils – can you sleep in the same room with one?
It depends on the model and fan speed. High-quality fan coils with a DC INVERTER motor achieve 22–28 dBA at low speed, which is comparable to the quiet noise of an air conditioner. Cheaper models with asynchronous motors can be 35–42 dBA at low speed, which some people find disturbing at night. Always choose models with a guaranteed noise level below 30 dBA at the lowest setting for bedrooms.
What happens if I forget to clean the filter?
A neglected filter gradually reduces air flow. The fan coil will stop cooling effectively, the heat exchanger may begin to frost (in extreme cases), condensate will not drain properly, and overflow of the tank may occur. In heating mode, performance drops, the fan overheats, and motor failure may occur. From practical experience, I recommend including filter cleaning in your regular monthly routine – it takes 5 minutes and extends the life of the device by years. More in the article Cleaning and maintenance of fan coils – filters, UVC lamps and regular service.
Can I install a fan coil myself, or do I need an installation company?
Hydraulic and electrical connections of a fan coil require a qualified person – the installer must be authorized for work with pressure equipment and electrical installation. Hanging the unit itself, preparing the space, or condensate drainage can be done by a layperson. Commissioning (hydraulic balancing, pressure testing, setting up the control) is always the work of a professional. A detailed procedure is in the article Installation of a fan coil – procedure, connection and commissioning.
How many fan coils can I connect to one chiller?
It depends on the chiller's capacity and the combined capacity of the fan coils. The designer must perform a hydraulic calculation – not only the total capacity must be considered, but also water flow rates, pressure losses in the distribution and even distribution. Roughly: a small 10 kW chiller can supply 4–8 fan coils in standard rooms. Always let the system be designed by a building services designer.
Conclusion
Selecting the right fan coil is a systematic task, not a one-time decision. You must consider the performance under your specific conditions (not just the catalog value), the type of mounting matching the construction possibilities, the number of pipes according to operational requirements, control adapted to comfort, and the correct accessories for reliable daily operation.
If you are unsure about any of the parameters, consult – a mistake in selecting a fan coil is hard to correct after the ceiling is closed or after handing over the building to the investor. Other detailed topics – from specific performance calculations, through installation procedures, control, to fault diagnosis – can be found in other articles of our Knowledge Center on Fan Coils, where answers to other Common
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