Frequently Asked Questions about Fan Coils

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Common questions about fancoils – expert answers from practice

Fancoils are among the most commonly used devices in professional heating and cooling of commercial spaces, but they are increasingly finding their way into family homes, apartments and smaller multifunctional buildings. Despite the fact that their principle is quite simple, customers and installers encounter many practical questions – from choosing the right type through the method of regulation to maintenance and common faults. In this article, I have gathered the most frequently asked questions that we deal with in our projects, and I have tried to answer them as practically as possible – the way I would explain them to an experienced installer who hasn't worked with fancoils yet, or to an investor who wants to really understand what is being installed in the ceiling void.

What is a fancoil and how does it work?

A fancoil (sometimes called a "ventilator radiator" in Slovak) is a device that combines a heat exchanger and a fan. The principle is as follows: hot or cold water flows through the exchanger, the fan blows air through this exchanger and heat (or cooling) is thus transferred directly into the room. Unlike a classic radiator, it does not require gravitational convection to distribute heat – the air is actively moving, which significantly shortens the warm-up time and improves the evenness of heat distribution in the room.

This principle has several key advantages: a fancoil can work with a lower water temperature than a traditional radiator (typically 35–45 °C for heating, 7–12 °C in cooling mode), making it ideal for heat pumps. At the same time, it can both heat and cool in one device – it all depends on what we supply to the exchanger.

What is the difference between a two-pipe and a four-pipe fancoil?

This is one of the first questions that comes up at every project meeting. The difference is fundamental and directly affects what the fancoil will be able to do and how much it will cost.

Two-pipe system has only one circuit – one water supply and one water return. Therefore, either hot or cold water flows through the fancoil, but not both at the same time. This means that the entire building either heats or cools – it is not possible to have heat in one room and cooling in another at the same time. Switching the season requires manual intervention in the hydraulics (opening/closing the appropriate valves on the manifold). A two-pipe connection is cheaper to install, but less flexible.

Four-pipe system has two independent circuits – one for hot water (heating) and one for cold water (cooling). In this case, the fancoil has two heat exchangers. The advantage is the possibility of simultaneous heating and cooling in different zones of the building, regardless of the season. It is typically used in administrative buildings, hotels or in places where internal gains (server rooms, sunny sides of buildings) are so large that they require cooling even in winter.

More about this decision can also be found in the article Two-pipe and four-pipe fancoil connections – the difference and when to use which in our Knowledge Centre.

What capacity fancoil do I need for my room?

Calculating the capacity of a fancoil is an area where improvisation really doesn't pay off. A fancoil that is too weak will not heat or cool the room sufficiently, while one that is too strong will unnecessarily increase investment costs and may cause unpleasant drafts or excessive noise at full capacity.

An approximate rule from practice speaks of 50–80 W/m² for heating and 60–100 W/m² for cooling – but these are very rough numbers that apply only to average insulated spaces with standard ceiling height (2.5–2.8 m). In practice, the following factors play a role:

Room heat loss – determined by the thickness and type of insulation, type of windows, and orientation to cardinal directions
Internal heat gains – people, lighting, electrical appliances (an office with 10 people and computers has completely different gains than an empty warehouse)
Ceiling height – with a ceiling of 4 m, you need significantly more, because the air volume is larger
Inlet water temperature – a fan coil with 45 °C water provides a different performance than the same model with 60 °C
Exterior temperature – it is dimensioned for the worst conditions (the calculated external temperature for the given area)

I recommend getting a thermal calculation for each order – either from an architect or at least a simplified energy simulation. More about calculations can be read in the article What fan coil capacity do I need for my room?.

Where and how are fan coils installed – what are the differences between the types?

Fan coils are delivered in several basic mounting configurations and the choice of the correct type has a direct impact on efficiency, aesthetics, and installation cost.

Ceiling (cassette) fan coils

They are mounted in the space above the dropped ceiling. The air is directed downward, or to 2 or 4 sides. They are practically invisible – only a cassette grid is visible under the ceiling. Ideal for office buildings, hotels, and commercial spaces. Disadvantage: sufficient space above the ceiling is required (at least 200–350 mm, depending on the model) and more demanding service access.

Under-ceiling (suspended) fan coils

They are suspended directly under the ceiling without a dropped ceiling. The air blows horizontally along the ceiling. They are visible, but their installation is simpler and cheaper than cassette types. Common in industrial spaces, garages, and commercial halls.

Parapet (under-window) fan coils

They are mounted on the floor, under the window sill. The air is blown upwards, eliminating the cold zone near the windows. This type is very popular in apartment buildings, apartments, and hotel rooms, because it looks similar to a classic radiator, but has a much higher performance in relation to its size.

Floor (duct) fan coils

They are installed in the floor, in a special duct. The air exits at the floor level and rises upwards. The solution is elegant and hidden, but it requires either a raised floor or installation during the rough construction phase. The IVAR SL, SLI, and SLS series belong precisely to this category – they are built-in floor fan coils, popular in single-family homes with glazed façades. Dimensions, installation requirements, and variants are described in detail in the article Dimensions and installation requirements of IVAR SL, SLI, and SLS fan coils.

For IVAR floor fan coils, an installation box for air conditioners and fan coils is available, which simplifies installation and ensures proper placement of the unit in the floor duct.

How does fan coil control work and what are the options?

Fan coil control is a topic we cover in great detail in a separate article Fan coil control – from a simple switch to smooth DC INVERTER control. Here we will limit ourselves to a basic overview that will help you understand the options.

Manual control

The simplest variant – a manual switch on the fan coil or a wall controller that selects the fan speed (usually 3 levels). No automation, no programming. Suitable for simple applications, summer cottages, warehouses. A typical example is control for IVAR.SL, SLS – built-in; 4-speed; 230V, which allows simple settings in four performance levels directly on the device.

Thermostatic control

A thermostat in the room measures the temperature and opens/closes the water valve or turns the fan on/off accordingly. Basic thermostatic control is mechanical (bimetal) or electronic. Electronic thermostats (with an LCD display, programmable by hours and days, with a night temperature drop) are now standard even in residential projects.

DC INVERTER control

Modern fan coils of the IVAR SLI series are equipped with DC motors with smooth speed control. Instead of switching between 3 speeds, the performance smoothly adjusts to the current need – from minimum speed (almost silent operation) to full performance. The advantages are clear: lower noise, energy savings, and longer motor life. An example of such a fan coil is an intake kit for IVAR.SLI DC 400, which is an accessory for this series of DC fan coils.

System Regulation (BMS, KNX, Modbus)

In commercial buildings, fancoils are connected to a central building control system (BMS – Building Management System). Each fancoil has its own control module that communicates with the central unit via a bus (Modbus RTU/TCP, BACnet, KNX). This enables central monitoring, operation scheduling, remote access, energy statistics, and other functions. For larger projects, this solution is economically justified, as energy savings from optimized operation are returned within a few years.

How noisy are fancoils and can the noise be reduced?

Noise is one of the most frequently discussed issues, especially in residential and hotel projects. A fancoil is always somewhat noisier than a radiator (which does not combine any moving parts), but modern devices are very quiet when properly set up.

Manufacturers specify the sound pressure level in decibels (dB(A)) for each speed level. Typical values for a floor-mounted fancoil in residential use:

1st speed (low): 28–34 dB(A) – almost inaudible, comparable to a quiet background in an office
2nd speed (medium): 35–42 dB(A) – gentle noise, most people perceive it as neutral
3rd speed (high): 42–52 dB(A) – more noticeable noise, perceptible in a quiet room

In practice, this means that with proper sizing (the fancoil does not operate at full capacity constantly), the noise is minimal. Noise problems most often arise in these situations:

Undersized fancoil – runs constantly at 3rd speed because it cannot cover the heat loss
Clogged filter – reduces air flow, the motor works harder, noise increases
Vibrations – caused by poor installation, loose parts or objects lying on the grille
Hydraulic noises – noise from water in the pipes, caused by improper air venting or excessively high water flow speed

DC INVERTER fancoils (IVAR SLI series) are significantly better in this regard than classic AC models, as the fan rotates exactly as fast as needed – no more.

What is the difference between built-in and wall-mounted fancoils?

We cover this question in detail in the article Built-in vs. Wall-mounted Fancoils – Which Solution is Suitable for My Project, but briefly: built-in fancoils are installed into a floor duct during construction or renovation – they are hidden, aesthetically neutral, but their installation is more demanding and must be planned in advance. Wall-mounted (parapet) fancoils are mounted on a finished wall, without demolition, making them a better choice for renovations of existing spaces.

What is a UVC lamp in a fancoil and why is it important?

A UVC lamp is an optional accessory installed directly into the fancoil and used to disinfect the air passing through the device. UV-C radiation (wavelength 200–280 nm) has a proven bactericidal and virucidal effect – it destroys bacteria, mold, and viruses circulating in the air or settling on the surface of the heat exchanger.

In the context of fancoils, this is particularly relevant because the heat exchanger operates under conditions (low temperature, condensing humidity) that promote the growth of microorganisms and mold. A UVC lamp eliminates these microorganisms continuously, without the need for chemical disinfection.

For IVAR SL and SLI series fancoils, a specially dimensioned UVC lamp for IVAR.SL, SLI 400 (L=475 mm) is available. It is important to use a lamp designed for a specific model – the correct length and radiation power ensure optimal disinfection without the risk of damaging the plastic parts of the fancoil.

UVC lamps have a limited lifespan – typically 8,000–12,000 hours of operation (which is approximately 1–1.5 years with year-round operation). After the lifespan expires, the radiation intensity decreases, although the lamp still appears to be lit, but its disinfecting effect is minimal. Therefore, it is important to monitor operating hours and replace the lamp regularly.

What accessories are needed for a fancoil?

A fancoil itself is only the heart of the system. To fully commission it, additional accessories are required, which vary according to the specific model and installation method.

Grilles and air intake kits

Air must have a place to enter the fancoil (intake grille) and a place to exit (outlet grille). In the case of built-in floor models, these are cover grilles for the duct. For example, the intake grille for IVAR.SLI DC 600 is specifically designed for this model and ensures proper air flow and aesthetic completion of the installation.

Control Valves and Actuators

On the hydraulic side, it is necessary to install a control valve (2-way or 3-way) with an electric or servo motor actuator. The actuator opens/closes the water supply based on a signal from the thermostat. Without it, the fancoil either continuously heats/cool or does not operate at all.

Condensate Tray and Condensate Drain

During cooling operation, atmospheric moisture condenses on the cold heat exchanger. This water (condensate) must be drained – either by gravity into the sewer, or by a condensate pump (if the fancoil is located below the drain pipe). A missing or clogged condensate drain is one of the most common causes of flooding – the condensate overflows from the tray onto the floor or into the ceiling structure.

Filters

Each fancoil has a built-in filter (usually G3 or G4 filtration class). The filter captures dust and impurities, protects the heat exchanger, and maintains hygiene. Filters must be regularly cleaned or replaced – more about this in the article Cleaning and Maintenance of Fancoils – Filters, UVC Lamps, and Regular Service.

What are typical installation errors with fancoils?

Over the years of working with customers and installers, I have encountered the same recurring mistakes. Here are the most common ones:

Insufficient air venting – air in the system causes noise (bubbling, knocking), reduces hydraulic performance, and can cause corrosion. Every fancoil must be properly vented during system startup.
Missing Y-filter before the water inlet – impurities in the system (welding residue, rust, sediment) clog valves and the heat exchanger. A Y-filter (strainer) is a cheap prevention against expensive repairs.
Incorrect fancoil position – some models must be horizontal, others can be tilted only by a certain angle. An incorrect slope causes condensate to drip onto the floor instead of into the drip pan.
Low water flow – with an underdimensioned pump or too long piping runs, the water flow through the fancoil heat exchanger may be insufficient, drastically reducing performance.
Forgotten insulation of cold pipe – the pipe bringing cold water (cooling) must be thermally insulated, otherwise atmospheric moisture condenses on it and drips onto the structure.
Missing balancing unit or pressure difference – fancoil systems must have properly hydraulically balanced branches, otherwise some fancoils get more water than needed and others less.

A detailed installation, connection, and startup procedure can be found in the article Mounting a fancoil – procedure, connection, and commissioning.

How long does a fancoil last and what affects its lifespan?

Properly installed and maintained fancoils should last 15–25 years. In practice, the weakest component is the fan motor – in cheaper AC models, it may fail after 10–12 years of intensive operation. DC motors in INVERTER models generally have a longer lifespan due to lower thermal stress from smooth speed regulation.

The biggest impact on lifespan is:

Water quality in the system – aggressive water (low pH, high oxygen content) corrodes the heat exchanger. The system should be filled with treated water with corrosion inhibitors and controlled pH (7.0–8.5).
Regular filter maintenance – a dirty filter overloads the motor, increases its temperature, and shortens its lifespan
Continuous operation at maximum speed – a sign of undersizing or incorrect thermostat setting
Condensate – if not drained properly, it causes corrosion of internal parts and mold growth

Can I use a fancoil with a heat pump?

Yes, and this is one of the most interesting combinations in modern heating. A heat pump is a source of low-temperature hot water (typically 35–55 °C) and a fancoil is an ideal terminal because, unlike floor heating, it reacts quickly and does not require a large thermal mass.

Key advantage: a fancoil works efficiently even at 35 °C water inlet temperature, while a conventional panel radiator would barely heat the room at such a temperature. A heat pump can achieve a COP (coefficient of performance) of 4–5 at 35 °C, meaning that for every 1 kW of electrical energy, it produces 4–5 kW of heat. In combination with a fancoil, you get a very efficient system with a fast response and active cooling (simply by reversing the heat pump cycle).

For cooling, it is necessary to have a fancoil with a condensate tray and drain – during cooling, water condenses and must be drained somewhere.

Frequently asked questions (FAQ)

Do I need to service my fancoil every year?

For standard spaces, it is sufficient to check and clean the filter once a year, check the condensate flow, and visually inspect the unit. In larger commercial spaces, hospitals, or facilities with higher hygiene requirements, servicing twice a year is recommended – in spring (before the cooling season) and in autumn (before the heating season). A fancoil with a UVC lamp also requires monitoring of the lamp's operating hours and replacement after its lifespan ends.

Why is my fancoil blowing cold air even though it is set to heat?

The most common cause is a closed or non-functional control valve – hot water is not reaching the heat exchanger, but the fan is running. Another possibility is an incorrectly set thermostat (the temperature on the thermostat is lower than the room temperature, the system thinks it is warm enough), or a dirty heat exchanger that does not transfer heat. You need to systematically check each of these points. More about troubleshooting can be found in the article Common fancoil faults and how to fix them.

Is it possible to connect a fancoil to an existing boiler and radiator system?

Technically yes, but it is more complicated than it seems. Radiator systems operate with higher water temperatures (60–80 °C) than fancoils require (40–55 °C). A direct connection would work, but the fancoil would be at full capacity permanently and thermostatic control would be problematic. The correct solution is hydraulic separation (a mixing unit) with a three-way valve that maintains the correct temperature for fancoils. Alternatively, fancoils can be connected to a separate low-temperature circuit with its own heat source.

What level of noise is normal and when should I call a service technician?

Mild fan noise (almost silent on 1st speed, more noticeable on 3rd speed) is normal. Abnormal are: metallic squeaking or whining (damaged motor bearing), clicking sounds (mechanical problem with the fan blade or foreign object in the fan), bubbling or gurgling (air in the system – needs to be vented), and loud humming at startup (vibrations – check the mounting). These symptoms require service intervention before major damage occurs.

What is the minimum ceiling height for a ceiling-mounted fancoil?

It depends on the model, but generally a ceiling (cassette) fancoil needs at least 200–280 mm of space above the dropped ceiling for the unit itself, plus another 100–150 mm for hydraulic and electrical connections. In total, at least 300–430 mm from the finished ceiling structure to the bottom edge of the dropped ceiling. For built-in floor-mounted fancoils IVAR SL/SLI, the decisive factor is the duct depth – typically 85–120 mm. Exact dimensions are in the article Dimensions and installation requirements of IVAR SL, SLI, and SLS fancoils.

Can a fancoil also be used for ventilation (supply of fresh air)?

Standard fancoils circulate air in the room – they recirculate indoor air through the heat exchanger and return it to the room. They do not supply fresh outdoor air. However, there are special models with fresh air mixing (so-called fan-coils with heat recovery or mixing dampers), which combine both functions. For ventilation in combination with a fancoil system, the most common solution is a separate ventilation unit with heat recovery, which covers the minimum air exchange requirements, while the fancoils provide heating and cooling.

Conclusion – what to watch out for with fancoils in short

Fancoils are an excellent solution for modern low-temperature systems with heat pumps, for commercial spaces requiring both heating and cooling, and for glazed single-family homes where floor heating cannot eliminate cold zones near large windows. Their biggest advantage is flexibility and fast response – which is more important than ever with the increasingly variable use of buildings.

The key to satisfaction with a fancoil installation is correct power calculation, correct choice of mounting type, quality hydraulics with balancing, regular filter maintenance, and – in terms of comfort – choosing a DC INVERTER model with smooth speed control. Investment in a better model with quality control pays off in the form of lower noise, energy savings, and longer device lifespan.

If you are considering a specific project and want to verify what type and power of fancoil is right for you, I recommend going through other articles in our Knowledge Center – especially How to choose a fancoil – power, mounting type, and number of pipes and What fancoil power do I need for my room, where you will find detailed calculation procedures and specific examples from practical experience.

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