Heat Pump Installation – Process, Requirements and Common Mistakes

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Heat pump installation – procedure, requirements and common mistakes

A heat pump is an investment for twenty or more years. If it is correctly dimensioned and professionally installed, it will work quietly, efficiently and without problems for most of the year. However, if something goes wrong during installation – a bad location of the outdoor unit, neglected hydraulics, incorrectly connected controller – it can mean unnecessarily high electricity bills, frequent breakdowns, premature compressor wear or even a warranty that the manufacturer will not recognize. That is why the topic of installation is so important and definitely deserves a longer and more detailed look than just a list of steps from the instruction leaflet.

In this article we will go through the entire process from start to finish: preparation of the building, requirements for electrical installation, hydraulic connection, unit placement, filling and starting the system, as well as typical mistakes that are repeated in almost every second job in practice. If you are still in the selection phase, we recommend reading the article How to choose a heat pump – what to focus on before buying and also What power of heat pump do I need for my house – without the correct setting of power and correct selection of type, there is no point in solving the installation.

Who is allowed to install a heat pump

The first and fundamental question: can you install a heat pump yourself? Partially yes, but not entirely. Legislation and warranty conditions of manufacturers create clear boundaries.

Refrigerant circuit – that is the part where the refrigerant (freon) flows – can be handled only by a certified person with a valid certificate according to Regulation (EU) No 517/2014 on fluorinated greenhouse gases (F-gases). In practice, this means that pre-filled split systems (outdoor + indoor unit connected by copper pipes) must be connected and commissioned by a certified technician. Monoblocks, where the entire refrigerant circuit is enclosed in one unit, do not touch the refrigerant part in principle – but checking the tightness and the first start-up is also recommended by manufacturers to be entrusted to a service organization.

Hydraulic part – water distribution, circulation pumps, distributors, expansion vessels – can be realized by an installer without a special certificate, or by an experienced DIY enthusiast. There is room for a home handyman, but he must know what he is doing.

Electrical connection – power cable, fusing, possibly a separate electricity meter for the tariff for the heat pump (HDO) – must be realized and signed by an electrician with authorization according to §22 or §23 of Act No. 124/2006 Coll.

This implies: at least two specialists usually participate in the complete installation of a heat pump – an electrician and an installer/technician of the heat pump. Some companies have them in one team, in others it is necessary to coordinate more tradesmen. It must be well planned in advance, because the inspection electrician and the refrigeration technician must be on site in the correct order.

Preparation before installation – what must be ready

The most common reason for prolonging the installation and unnecessary visits of technicians is the unpreparedness of the building. Here is an overview of what must be ready before the installers arrive.

Construction readiness

The place for the outdoor unit (concrete foundation, wall bracket or roof structure) must be ready and dry.
The wall penetration for refrigerant pipes and electrical cables must be drilled and protected with a sleeve (min. ∅ 60 mm for a two-pipe split, min. ∅ 100 mm if multiple cables also pass through).
The place for the indoor unit (tank, buffer or combined boiler) must be free and accessible from at least two sides for 60 cm – for service interventions.
The boiler room or technical room must have a floor drain or the possibility of connecting the condensate pipe (with a hydraulic unit, water is inevitably used during bleeding and servicing).
If it is a ground-water heat pump: boreholes or ground collectors must be completed, filled with brine (glycol) and the flow through them must be clearly ensured.

Electrical readiness

A separate electrical circuit for the heat pump – most units up to 12 kW require a 3×16 A circuit breaker, more powerful ones 3×25 A or more. The exact values are always in the technical sheet of the specific device.
The cable must be of sufficient cross-section – for a 12 kW heat pump it is usually CYKY 5×4 mm², for more powerful ones 5×6 mm² or more (depending on the length of the route).
If you want to use the favorable HDO tariff (two-tier), you need to ask the distributor in advance to install the HDO receiver and the necessary fusing – this process can take up to 4–8 weeks, so you need to start almost immediately!
For communication cables (control signal, thermostat, external temperature sensor), it is necessary to run signal cable UTP or JYSTY 2×0,5 according to the manufacturer's specifications.

Hydraulic readiness

Piping in the heating system must be completed and flushed – heat pumps are sensitive to impurities, and if construction dust or sludge from other installations enters them, it can damage the circulation pump or the plate heat exchanger.
If the heat pump is installed to an existing heating system (e.g. replacing a gas boiler), the old system must be flushed and the magnetite sludge removed – see below in the section on flushing.

Placement of the outdoor unit – principles that must not be overlooked

The outdoor air-to-water unit is, from the perspective of physical laws, a fan and a heat exchanger. It works by drawing in air, cooling it (in winter it "takes" heat from it), and then discharging the air outside. Therefore, it must have enough space for air circulation – and this is where many people make mistakes.

Minimum clearances

Each manufacturer specifies exact minimum distances in the installation manual. General recommendations are:

In front of the fan exhaust: min. 1.5 m of free space, ideally 2 m or more. If there is a wall or fence in front of the unit, the air is recirculated – the unit draws in pre-cooled air, COP drops and in freezing conditions it may fall below the operational limit.
Sides: min. 30–50 cm (depending on the model).
Above the unit: min. 50 cm (for top exhaust) or no limit (for front exhaust).
Distance from the neighbor's boundary: min. 2 m (noise emissions), in some municipalities stricter local regulations apply.

Orientation and prevention of freezing

The unit should not be placed directly under a downspout or in a place where a lot of snow falls. During defrosting (defrost cycle), condensate drips down – it must have a place to drain. The condensate drain should be connected either elevated to the sewer or into a gravel pit. In freezing conditions, condensate can freeze under the unit and create a dangerous icy surface – that is why some models offer a self-regulating heating cable, which heats the drain pipe and prevents freezing. In practice, we recommend it everywhere where the condensate drain goes outside or through unheated areas.

Foundation or bracket

The outdoor unit must be placed on a solid base. A concrete foundation is ideal – thickness min. 12–15 cm, protruding min. 5 cm above the ground (to prevent surface snow from reaching it). An alternative are rubber anti-vibration pads or special steel brackets for the wall. Wall brackets for facade mounting are practical, but they must be anchored into a load-bearing wall (not into insulation!) and anti-vibration rubber should be used between the bracket and the unit – otherwise vibrations are directly transferred into the building and are very disturbing in the quiet of the night.

Hydraulic connection – the core of the entire installation

The hydraulic scheme of a heat pump is usually more complex than people imagine. It is not enough to connect the unit's inlet and outlet to an existing circuit – it is also necessary to properly address hydraulic separation of circuits, expansion tank, safety valve, filtration, air venting, and regulation.

Direct and indirect connection

The heat pump can operate in so-called direct connection – where the circulation pump in the unit drives water directly through the heating circuits. This is simple and efficient for small houses with one circuit and floor heating. If the house is larger and has multiple circuits (floor + radiators, pool circuit, domestic hot water), it is necessary to use a hydraulic buffer tank or a combined tank, through which the circuits are separated and each has its own circulation pump and regulation.

During installation, for specific models (e.g. connection kit for CALIBRA DUO and ATLAS DUO series), the manufacturer precisely defines how and where the unit should be connected to the distribution – including the correct flow direction and the need for a backwash filter. These connection kits eliminate most improvisation and are designed so that no warranty issues arise during installation.

Expansion tank and safety valve

The expansion tank must be properly sized for the total volume of water in the system. Too small an expansion tank causes the safety valve to regularly drip – which damages the valve seat and gradually leads to leakage. Basic calculation: expansion tank volume = 10–15 % of the total water volume in the system, at least 12 liters for a typical family house. The tank's gas pre-charge must correspond to the system's static height (usually 1–1.5 bar for a single-story house, 1.5–2 bar for a two-story house).

The safety valve for the heat pump usually opens at 3 bar – this must be checked and recorded in the installation protocol.

Filtration and magnetite sludge

This is a topic that installers often dismiss with the phrase "it will be fine" – and then after a year the tank or heat exchanger is clogged with black sludge (magnetite). Magnetite is iron oxide that is released during corrosion of steel radiators and pipes in the presence of oxygen and water. Heat pumps are sensitive to it because they have small cross-sectional diameters in the heat exchanger.

Solution: install a magnetic filter before the heat pump (on the inlet side) – either a simple ball filter with a magnet or an automatic magnetic separator. The filter must be cleaned once a year (during annual service). If a heat pump is installed in an existing system with a boiler, the system should be chemically flushed (flushing) and then neutralized before installation – this is a half-day job, but it prevents problems for years.

Domestic hot water

Most modern heat pumps can also heat domestic hot water (DHW), either through an integrated tank or through an external boiler with a heat exchanger. To ensure hot water circulation in the house (so that you don't have to wait long for hot water at a distant outlet), a special hot water circulation set compatible with models ITEC-T, ATHENA-T, LEGEND, CALIBRA and ATLAS can be used. This set includes all necessary components including a small circulation pump, timer and check valve – installation is relatively straightforward, but it must be considered in the overall control scheme to prevent the circulation from unnecessarily overheating the tank and reducing efficiency. More on this topic can be found in the article Integration of hot water circulation with a heat pump – how to do it.

Electrical connection and control

The electrical installation of a heat pump is two-layered: high-current (power supply) and low-current (control, communication).

Power supply

Three-phase heat pumps (now standard for capacities over 6 kW) require a four- or five-core power supply (L1, L2, L3, N, PE). Passage through a 300 mA RCD is mandatory. The installation must be completed before the electrical inspector issues a certificate – without it, the distributor will not activate the HDO or assign a meter.

HDO and favorable tariff

Most households in Slovakia can request tariffs DD5 or DD6 (or their equivalents according to the distributor), where the distribution rate for electricity for the heat pump is lower, but the distributor reserves the right to limit the supply (HDO – mass remote control) for several hours per day. The heat pump must be able to withstand these interruptions – most modern units can do so thanks to accumulation in the buffer tank. Important: the HDO signal must be connected correctly, otherwise the HP will either stop all day or stop exactly when electricity is cheapest.

Control and control signals

Modern heat pumps are controlled equithermally – the temperature of the supply water automatically adjusts to the outside temperature according to the set heating curves. This means that an outdoor temperature sensor must be installed – usually on the north side of the building, out of direct sunlight and protected from rain. Incorrect placement of the sensor (on the sunny side, above the exhaust of an appliance) causes systematic control errors.

For more complex systems with multiple mixing circuits, it may be necessary to expand the control via expansion module for ITEC models, which adds inputs and outputs for additional circuits, tanks or external devices. When and why you need it is described in more detail in the article Expansion module for heat pump – when and why you need it.

When connecting a mixing circuit (e.g. for radiators with a three-way valve) to heat pumps that output a modulated 3–10 V signal, a signal converter is required. For example, relay kit for diplomat Optimum G3 converts the analog 3–10 V signal to a standard on/off output, allowing a standard circulation pump of the mixing circuit to be connected without the need to purchase an expensive ECM pump with an analog input.

Filling the system, degassing and pressure test

After completing the hydraulic connection, the system is filled. This step is as important as the installation itself – a poorly degassed or under-pressurized system causes cavitation in the circulation pump, noise, and in the worst case, damage to the heat exchanger.

Filling procedure

Check that all air vents are open (automatic and manual).
Fill slowly from the lowest point of the system – never from the top.
Let air escape from all degassing points until only water flows.
Set the filling pressure to 1.5–2 bar (cold system).
Run the circulation pump for 5 minutes and check the pressure – if it drops, top up.
Repeat degassing in all circuits.
Perform a pressure test at 1.3 times the operating pressure (i.e. for a 3-bar system, test at 3.9 bar) for at least 30 minutes.

It is advisable to add a corrosion inhibitor (e.g. based on molybdate) and biocide to the water in the system – this significantly extends the life of the system and reduces the formation of magnetite. The concentration and type of preparation must be in accordance with the manufacturer's recommendations for the HP.

Setting the control and first start-up

The first start-up of a heat pump is the technically most critical moment of the entire installation. At this moment, it is verified whether everything has been connected correctly, and the controller is set to the real parameters of the house.

Setting the heating curves

The heating curve defines what temperature of the supply water the HP should prepare at a specific outside temperature. For example: at –15 °C outside → 45 °C supply water for the floor, at +5 °C outside → 28 °C supply water. The curve is set in the controller and must correspond to the real characteristics of the heating system. Too steep a curve → overheated rooms, unnecessary consumption. Too flat a curve → insufficient heating in the cold.

In practice, the curve is set iteratively – after the first setting, it is monitored for several days and corrected according to the house's reaction. Therefore, it is good if the technician comes for a check after the first week of operation in the winter period.

Setting legionella protection

If the heat pump also heats DHW, the controller must be set to raise the DHW tank temperature to a minimum of 60 °C once a week (or according to EN 806 standard) (thermal disinfection – protection against legionella). This cannot be achieved by the heat pump alone at low outdoor temperatures – therefore, most units have an integrated electric booster (bivalent element), which takes over this role during the cycle. It is important to verify that this function is activated and correctly set.

Most common installation errors of heat pumps

Based on dozens of installation jobs and service visits, we summarize here the errors that are repeated. Some are minor and easily fixable, while others cost the customer thousands of euros in the form of high consumption or a damaged compressor.

1. Primary DHW tank or buffer too small

Heat pumps operate most efficiently when running longer cycles (30–90 minutes), not when turning on and off every 5–10 minutes. A too small tank causes so-called short cycling – the compressor turns on and off too often, which significantly shortens its lifespan. For a family house with 4 people, a minimum suitable DHW tank is 200–250 liters, 300 liters for larger families. A buffer for heating should have at least 30–50 liters per kilowatt of heat pump capacity.

2. Poor location of the outdoor temperature sensor

A sensor placed on a south-facing wall or near a kitchen exhaust in winter shows a higher temperature than reality. The heat pump thinks it is warmer outside and reduces the water output temperature – result: the house is cold, but the heat pump doesn't admit it. Solution: always place the sensor on a north or northwest wall, at least 2.5 m from the ground, protected by a small roof.

3. Insufficient flow in the hydraulic circuit

The heat pump requires a minimum water flow through the heat exchanger – insufficient flow (narrow pipe, clogged filter, forgotten closed valve) causes a shutdown to protect against high pressure in the refrigerant circuit. Error codes vary (E4, H3, etc. depending on the manufacturer), but the cause is always the same. Before starting, check that all valves are open and that the flow meter (if present) shows the correct value.

4. Missing or incorrectly set safety valve

The safety valve on the DHW tank must be connected with a drain – i.e. a pipe leading to a floor drain. If the drain is missing, during every thermal expansion water from the safety valve flows onto the floor or electrical installation. This is not just an inconvenience, but a safety risk.

5. Incorrectly set heating curve

If the technician sets the curve "by eye" without analyzing the house, the system either overheats (uses more electricity) or underheats (the house is cold). Correct setting takes several days of tuning and requires the technician to respond to customer feedback from the first frosty nights.

6. Ignoring the manufacturer's warranty conditions

Many customers have the heat pump installed by "a friend – an electrician" without an F-gas certificate, without professional first start-up, without an entry in the service log. At the first failure, the manufacturer will refuse warranty service – and since the compressor costs 800–2,000 euros or more, it is a painful lesson. Always ask the installer for a copy of the service log and the F-gas worker certificate.

Heat pump and existing heating – renovation versus new construction

In new construction, the hydraulics are designed to measure – ideally floor heating, correct tanks, copper or plastic piping. Renovation is a different matter: existing radiators, steel piping, perhaps an old boiler as a bivalent backup.

During renovation, consider the following:

Calculate whether existing radiators are sufficient for the low output temperatures of the heat pump (45–55 °C). If the boiler was set to 70–80 °C and the radiators were selected for that temperature, at 50 °C from the heat pump they will be undersized and rooms will not warm up. In that case, you need to add radiators or enlarge existing ones.
System flushing (see above) – do not skip even during minor renovations.
Hydraulic separation of the old and new circuits – if the gas boiler is kept as a bivalent source, both sources must be hydraulically and regulation-wise separated to avoid interference.

More on the choice between types of heat pumps and when it is worth renovating with an existing system can be found in the article Air-to-water heat pump vs. ground-to-water – which is more profitable.

Installation protocol and handover of the work

Proper installation does not end with turning on the heat pump. Handover of the work must include:

Completed installation/service protocol with date, names of technicians, set values, pressures, set curves.
Copy of the electrical inspection report.
Copy of the worker's F-gas certificate (for split systems).
Record of the pressure test of the hydraulics.
Customer instruction: how to set the room thermostat, how to read error codes, where the main switch of the heat pump is, where the safety valve is, where the filter is and how to clean it.
Setting the date of the first annual service – ideally before the winter season.

Without these documents, the customer runs into problems when making a complaint, when applying for a subsidy (e.g. the Green Home program) and when selling the property.

Most Frequently Asked Questions (FAQ)

Can I install an air-to-water heat pump myself if I am handy and know heating systems?

The hydraulic part (pipework, buffer tank, circulation pumps) can be handled by an experienced plumber or technically skilled handyman. However, the refrigerant part (if it is a split system) and the electrical connection must be carried out by a certified person – otherwise you risk losing the warranty, rejection of subsidies, and in the case of a refrigerant-related failure, legal liability. Monoblocks are simpler in this respect, but manufacturers usually require professional first start-up as well.

How long does the full installation of a heat pump take?

For a typical single-family house (monoblock air-to-water, new installation, TÜV tank 200 l, buffer): 2–3 working days for an experienced two-person team. If it is a renovation with pipe replacement, new pipe laying, or a customer where you need to coordinate with an electrician, mason, and plumber, realistically expect a week of work spread over several days.

What to do if the heat pump throws an error code right after startup?

Note the code and do not turn off the heat pump forcefully – let it enter the error state on its own and restart it. If the error repeats, contact the installation company. The most common causes after a new installation: insufficient flow (closed valve, insufficiently filled system), air in the heat exchanger, too low outside temperature at first start (some models refuse to start below –10 °C without preheating), or incorrect temperature sensor wiring. The article Common heat pump faults and how to recognize them contains a detailed overview of codes and their causes.

Must the outdoor unit of the heat pump be reported to the building authority?

In Slovakia, the outdoor unit of an air-to-water heat pump at a single-family house is usually considered a technological device, not a building – and typically no notification or building permit is required. Exceptions are locations with special conditions (heritage zones, zoning plans with noise restrictions). Always check the current status at the local building authority, as regulations may vary from one municipality to another and the situation is evolving.

What are the installation costs of a heat pump (excluding the cost of the equipment)?

It depends heavily on the scope of work. Roughly for a single-family house: installation of the unit and tank 800–1 500 €, electrical installation 400–800 €, hydraulics (if new pipework or manifold is needed) 600–2 000 € and more. Overall, a full "turnkey" installation from a reputable company costs 2 000–5 000 € for an average single-family house – excluding the cost of the heat pump. Prices vary by region and complexity of the job.

Why is the heat pump noisier after installation than expected?

Vibrations and noise after installation can have multiple causes: the outdoor unit is not mounted on anti-vibration pads, the bracket is anchored into a hollow wall, refrigerant pipes touch the wall and transfer vibrations to the structure, or there is air in the hydraulic circuit (hydraulic noise – "hissing" of water in the pipes). Most of these problems can be fixed without major intervention – it is necessary to identify the source and eliminate it. A more detailed discussion is available in the article Maintenance and service of heat pumps – what you can do yourself and what you cannot.

Conclusion

Installation of a heat pump is not complicated if approached systematically and with sufficient preparation. Most of the problems customers encounter after installation – high consumption, noise, outages, cold house – have their roots in specific decisions made (or not made) during installation. A properly dimensioned system, professionally designed hydraulics, qualified technicians, and thorough regulation setup are an investment that pays off in reliability and low operating costs for the entire life of the equipment.

If you are considering a heat pump and have not yet decided which type and capacity is suitable for you, we recommend starting with the articles How to choose a heat pump – what to focus on before purchase and What capacity of heat pump do I need for my house. If you already have the equipment and are dealing with connecting accessories, also see Connecting and installing heat pump accessories step by step.

Do you have a question on this topic?

Not sure or dealing with a specific situation in your household? Write to us – we are happy to help.