Installation of Fan Coil - Procedure, Connection and Commissioning

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Installation of a fan coil – complete step-by-step process from preparation to commissioning

A fan coil unit, when properly installed, can operate for years without problems. However, incorrect installation can lead to issues such as noise, leaks, inefficient performance, or repeated freezing of the heat exchanger. From practical experience, I know that most fan coil problems do not arise from the product itself, but from installation errors – incorrect slope, poor electrical installation, or neglecting condensate drainage. This article will guide you through the entire installation process step by step, including hydraulic connections, electrical installation, setting up the control system, and the first start-up.

If you are still in the phase of choosing the right device, I recommend first reading the article How to choose a fan coil – performance, type of installation and number of pipes or What fan coil capacity do I need for my room. Here we assume that you have already selected the device and are ready to install it physically.

What you will need before the actual installation

Preparation is just as important as the installation itself. Underestimating the preparation phase often leads to missing materials on site, flow control valves being ordered additionally, or discovering that the installation hole in the drywall has incorrect dimensions. Here is a list of what needs to be prepared before installation:

Technical documentation for the fan coil – installation manual, dimensional drawing, wiring diagram. Do not install anything without it.
Hydraulic connections – the piping for heating/cooling water must be ready at the correct location, with insulated supply and return lines, and a vent valve at the highest point.
Adjusting/balancing valves – the flow through the fan coil must be adjustable and closable without draining the entire system.
P-trap or condensate pump – condensate drainage is mandatory for cooling, not optional.
Electrical connection – 230 V with a protective conductor, optionally a signal cable for an external thermostat or BMS.
Tools – drill, spirit level, torque wrench, manometer, electrical testing device.
Sealing and installation accessories – thread sealant, hemp fiber or PTFE tape, fittings, brackets.

For built-in (cassette or ducted) fan coils, do not forget the installation space. The product Installation box for air conditioners and fan coils addresses situations where you need protection for the device during construction or a standardized installation frame for suspended ceilings.

Types of installation and their specifics

Fan coils can be installed in several ways depending on their construction type. Each type has different space preparation requirements, different media supply directions, and different condensate drainage locations.

Wall-mounted fan coils

These are mounted on the wall similarly to a split unit. The advantage is easy access to the filter, simple maintenance, and visible installation that can be checked at any time. The disadvantage is the visibility of the device in the interior. Hydraulic connections come from the back or side and must be insulated to prevent condensation on cold pipes. A more detailed comparison can be found in the article Recessed vs. wall-mounted fan coils – which solution is suitable for my project.

Recessed (cassette and ducted) fan coils

These are installed in a suspended ceiling or in an interstitial space. Only the decorative grille or cassette is visible. Before covering with the ceiling, the entire hydraulics, electrical system, and condensate drainage must be tested and functional – later repairs are expensive. Products such as Air intake kit for IVAR.SLI DC 400 or Air intake grille for IVAR.SLI DC 600 ensure proper airflow to the hidden device without unnecessary pressure losses.

Floor-mounted fan coils (parapet and ceiling)

Floor and parapet units combine the advantages of visibility with compact dimensions. Hydraulic connections are usually bottom-mounted, and condensate drains by gravity directly into the sewer or a trap under the device. Dimensional requirements for specific IVAR SL, SLI, and SLS models can be found in the article Dimensions and installation requirements for IVAR SL, SLI, and SLS fan coils.

Installation step by step

Step 1 – Marking the location and securing

The location of the fan coil is not random. For wall-mounted units, the fan coil must be placed so that the air flow covers the entire room, with the air discharge directed downward along the wall (for heating) or horizontally (for cooling). It is usually installed under the ceiling at a height of 200–220 cm from the floor, so that the air circulates well.

For built-in units, the location is determined by the room layout, the location of the piping, and the availability of an access opening. Never skip the access opening – a fan coil in a ceiling without access is not serviceable.

The mounting must be dimensioned for the weight of the device plus the weight of the water in the heat exchanger. A larger IVAR SLI fan coil can weigh 15–25 kg, and with water and a condensate tray, it can easily reach 30 kg. Anchors must be fixed into the load-bearing structure, not just into drywall.

Step 2 – Mechanical installation of the fan coil body

After securing the load-bearing structure (angles, threaded rods, rails), attach the fan coil body according to the instructions. Most built-in fan coils are suspended on two or four M8 or M10 threaded rods. Check the horizontal plane with a spirit level – a deviation of more than 2–3 mm per meter will cause condensate to pool in the tray and not flow into the drain.

For floor-mounted units, adjust the feet or shims so that the condensate drain is always at the lowest point of the tray. A slope of 1–2 % (1–2 cm per meter) toward the drain is standard.

Step 3 – Hydraulic Connection

The hydraulic connection is the core of the entire installation and also the most common source of errors. Several principles must not be violated:

Two-pipe vs. four-pipe system – determines the number of connections on the fan coil. In a two-pipe system, you have supply and return through one heat exchanger. In a four-pipe system, there are separate circuits for heating and cooling. More in the article Two-pipe and four-pipe fan coil connections – the difference and when to use which.
Orientation of supply and return piping – supply (warmer water) usually goes to the upper connection of the heat exchanger during heating; the order does not change during cooling (cold water enters the same connection). Always verify in the specific model's manual.
Balancing valves – each fan coil must have the possibility of individual flow adjustment. Recommended flow for a two-pipe fan coil with a power of 1 000–3 000 W is 60–180 l/h, precisely according to the power and heat exchanger parameters.
Closing valves – a ball valve on the supply and return allows for maintenance without draining the system.
Draining air – an automatic air vent at the highest point of the fan coil circuit. For concealed units, install an automatic air vent on the piping before it enters the ceiling void to ensure accessibility.

Seal threaded connections with hemp and paste or high-quality PTFE tape – 3–4 turns of tape around, not less. Tighten connections using torque wrenches, not "as tight as possible" – for brass fittings R ¾" the torque is 35–45 Nm, for R ½" 20–30 Nm. A cracked brass fitting in a ceiling void is an expensive matter.

After connecting the piping, fill the system and perform a pressure test at least 1.5 times the operating pressure, not less than 6 bar, for 30 minutes. The pressure must not drop by more than 0.1 bar. Do this before covering the ceiling void.

Step 4 – Condensate Drain Connection

During cooling, moisture from the air condenses on the cold heat exchanger and runs into the tray. The amount of condensate depends on the air humidity and the fan coil's power – for a typical office fan coil with a cooling capacity of 3 kW and 60 % air humidity, it can be 0.5–1.5 liters per hour. In an 8-hour workday, that's 4–12 liters. I'm not just explaining this for interest – if the condensate doesn't drain somewhere, in a week you'll have a wet ceiling or a floating ceiling void.

Resolve the condensate drain as follows:

Drain into the sewer – pipe at least DN 20–25 mm, slope at least 1 cm/m, ending in a trap to prevent odors from the flush pipe returning into the fan coil space. The trap must be accessible for cleaning.
Condensate pump – if a slope is not possible (e.g., a fan coil in the center of a room in a ceiling void). The pump has a small tank, a float switch, and a hose that pushes condensate into the sewer. Many pumps also have a safety output – in case of failure, they trigger an alarm or stop the fan coil.

Step 5 – Electrical Installation

Fan coils require 230 V / 50 Hz, and a protective conductor is mandatory. The supply must be protected by a B10 or B16 circuit breaker according to the motor power. Each fan coil should have its own circuit breaker – during maintenance, you want to disconnect the fan coil without having to shut down the entire circuit breaker group.

The electrical connection varies according to the type of control:

Local switch or 4-speed control – power goes directly to the fan coil, the controller is connected to the appropriate terminals on the control board. Product Regulácia pre IVAR.SL, SLS – vstavaná, 4-rýchlostná, 230V is a typical example of this solution – simple, reliable, without the need for an external control unit.
External thermostat – the thermostat (e.g., room thermostat) controls the opening of the valve and also turns the fan on and off via signal wires. Most thermostats for fan coils work with a 0–10 V or PWM signal to control the fan speed.
DC INVERTER control – modern fan coils with EC/DC motors (e.g., IVAR.SLI DC) require DC control, where the fan speed is continuously adjustable from 10 % to 100 %. This is a significantly more energy-efficient solution. More about the differences in the article Regulácia fancoilov – od jednoduchého spínača po plynulú DC INVERTER reguláciu.
BMS/KNX integration – in commercial projects, the building control system sends commands via Modbus RTU or KNX. Here, it is essential to follow the bus connection diagrams and device addressing.

Step 6 – Grounding and protection against condensation on pipes

The cold water supply pipe (for cooling) must be fully insulated with vapor barrier insulation of at least 13–19 mm thickness, depending on temperature differences and ambient humidity. On uninsulated sections of the pipes, water will condense from the surrounding air, which then drips onto the ceiling or into the suspended ceiling. This is a source of moisture damage, to which many installers are unprepared during the first fan coil installation.

Grounding of metal pipes and the fan coil body is mandatory according to STN 33 2000-4-41. Use a green-yellow conductor with a minimum cross-section of 2.5 mm².

First start-up and adjustment

Hydraulic circuit air venting

After filling the system, you must individually vent each fan coil. Procedure: turn on the circulation pump, open the ball valves of the fan coil, wait 5–10 minutes, then carefully open the air vent until water starts to flow without bubbles. If the fan coil fan still makes bubble-like noises after closing the air vent, keep the vent open for a while – air remains in the heat exchanger.

Typical mistake: the installer vents the fan coil at an incomplete system pressure. Air remains in the circuit and is released when full pressure is reached. Always vent at full working pressure of the system (1.5–2.5 bar).

Flow rate adjustment

Each fan coil has a specified design flow rate. If you set the flow rate too high, the fan coil will achieve full performance, but the rest of the system will suffer from hydraulic imbalance. If the flow rate is too low, the fan coil performance will be reduced and the heat exchanger may freeze during cooling. Adjusting the balancing valve according to the design documentation is a basic requirement for every installation.

If you do not have flow meters, orient yourself by the temperature difference between supply and return: with correct flow and full performance, the difference should be 5–10 °C for heating and 5–8 °C for cooling. A larger difference = low flow. A smaller difference = flow is too high.

Condensate drainage check

Before closing the suspended ceiling, run the fan coil in cooling mode for 30–60 minutes and check whether the condensate drains smoothly. Pour a glass of water into the pan and observe whether it drains – this will verify the slope and functionality of the trap without waiting for condensate from the heat exchanger.

Electrical and control function test

Turn on the device and gradually switch through all fan speeds. The fan must run smoothly, without rattling or vibrations. Check whether the thermostat correctly turns the fan coil on and off. If a control valve (2-way or 3-way) is connected, verify that it opens and closes according to the thermostat signal.

More about diagnostics and solving possible problems after start-up can be found in the article Common fan coil faults and how to eliminate them.

Hygienic accessories – UVC lamps and filters

The fan coil draws air from the room through a filter and blows it back. The heat exchanger is constantly moist (during cooling), which is an ideal environment for the growth of microorganisms and mold. In healthcare facilities, hotels, or office buildings with high occupancy, it is advisable to add hygienic components to the fan coil.

The product UVC lamp for fancoils IVAR.SL, SLI 400 – L=475 mm is designed directly into the fan coil body and sterilizes the air and the heat exchanger surface with UV-C radiation. It is installed into the device body before closing the suspended ceiling. The lamp has a limited lifespan (usually 8 000–12 000 hours), after which it must be replaced – plan this into your maintenance schedule.

The fan coil filter (usually G3 or G4 filtration class) is the first shield against contamination of the heat exchanger. A clogged filter increases air resistance, reduces performance, and can cause the heat exchanger to freeze. Cleaning and filter replacement are described in the article Cleaning and maintenance of fancoils – filters, UVC lamps and regular service.

Typical installation errors – from practice

Over the years of working with custom installations, I have repeatedly seen the same mistakes. The list below may save you a lot of trouble:

Missing trap on condensate drainage – condensate drains away, but unpleasant odors return from the drain pipe. A trap is mandatory whenever the drain connects to the sewer system.
Insufficient insulation of cold pipes – condensation forms on the pipes and drips onto the ceiling. Solution: vapor barrier insulation with a minimum thickness of 13 mm, joints sealed with insulation tape without gaps.
Reversed supply/return connection – the fan coil runs, but with significantly reduced performance during heating or cooling. Always check the flow direction according to the instructions.
Air vent not installed – air remains in the circuit, the fan makes bubbling noises, performance drops. An air vent must be installed at the highest point of each branch.
Fan coil installed without access panel – the filter cannot be cleaned, maintenance is expensive, the device stops being used after 2 years because it is "too noisy". Always plan an access panel of at least 30 × 30 cm to the filter and electrical components.
Poor flow rate dimensioning – we set the flow rate by guesswork instead of according to the design. Result: hydraulic imbalance of the entire system, some rooms are overheated, others are too cold.
Missing pressure test before covering – you discover a leak after a month when the drywall ceiling starts to discolor. A pressure test takes 30 minutes and costs less than one ceiling repair.

Handover and Documentation

After successful commissioning, prepare a handover protocol that includes:

type and serial number of each fan coil unit,
measured supply and return water temperatures at full load,
balancing valve settings (number of turns or Kv value),
pressure test – date, pressure value, result,
regulation and thermostat settings (temperature setpoint, sensitivity),
contact information for the service technician and recommended maintenance interval.

The customer must be instructed on where the filter is located, how to clean it (or request service), and what to do if the condensate tray starts to overflow (turn off the unit and call service). Also, leave them a copy of the technical manual.

Most Frequently Asked Questions about Fan Coil Installation (FAQ)

Can I connect a fan coil directly to the boiler without a manifold?

Technically yes, but it is not recommended for larger systems. A fan coil is a variable flow circuit (a control valve opens and closes it), which disrupts the hydraulic balance of other circuits (floor heating, radiators). The correct solution is hydraulic separation via a mixing unit, hydraulic balancer, or a manifold with its own circulation pump for the fan coil circuit.

What is the minimum water temperature at which a fan coil cools sufficiently?

The standard supply water temperature for fan coil cooling is 6–8 °C (temperature drop 6/12 °C). At this temperature, the heat exchanger condenses air humidity and achieves full cooling and dehumidification performance. If the water is 12–14 °C (cooled water from a heat pump), the fan coil still cools, but condensation is almost non-existent and the dehumidification effect is minimal. This must be considered during sizing.

Can one thermostat control multiple fan coils in one zone?

Yes, if the fan coils are in the same thermal zone and have the same temperature requirements. The thermostat switches on/off the valves (or fans) of all fan coils in the zone simultaneously. Each fan coil must have its own power supply and electric valve – the thermostat switches them in parallel via output relays. This solution is common in hotel rooms with multiple fan coils (e.g., room + bathroom).

Must I necessarily service a fan coil and how often?

There is no legal requirement for servicing residential fan coils, but the manufacturer usually conditions the warranty on regular maintenance (filter cleaning every 3–6 months, heat exchanger inspection once a year). In commercial buildings, regular HVAC maintenance is mandatory according to hygiene regulations. Neglected maintenance leads to increased energy consumption (clogged filter = higher motor power), reduced performance, and worsened air quality. More in the article Cleaning and Maintenance of Fan Coils – Filters, UVC Lamps, and Regular Service.

What to do if a fan coil makes a loud whirring sound after startup?

A whirring or bubbling sound after startup indicates air in the hydraulic circuit. Bleed the unit at full system working pressure. If the sound persists, check whether the balancing valve is sufficiently open (too low flow causes turbulent flow). A mechanical squeaking or rattling sound comes from the fan or bearings – in this case, turn off the unit and call service. More detailed diagnostics can be found in the article Common Fan Coil Faults and How to Fix Them.

Is any special inspection required before handing over the building?

For single-family homes and apartments, no separate inspection of the fan coil system is required, but the electrical installation (including fan coil power supply) must be subject to an electrical inspection according to STN 33 0000-6. For commercial and industrial buildings, the authorities require documentation on pressure tests, equipment settings, and in some cases also an energy audit report. The HVAC and cooling design may also require supervision by an authorized engineer.

Conclusion

Installing a fan coil is not rocket science, but it requires a systematic approach, adherence to technical discipline, and no shortcuts in any phase – from preparation and mounting, through hydraulics, electrical work and condensate drainage, to functional testing and handover with documentation. Every omitted pressure test, every missing trap, or every meter of uninsulated cold pipe will come back to you as a complaint or malfunction at the worst possible time – usually on a hot summer day or in the middle of winter frost.

If you are planning an installation or designing a fan coil system and are unsure about selecting accessories – such as intake kits, air grilles, control components, or hygiene accessories – check the category fan coils on atria.sk, where you can also find filtered search by device model.

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