Heat Pump Installation - What You Need to Know

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Why correct heat pump installation matters just as much as choosing the right unit

From an engineering standpoint, a heat pump is a reliable appliance - yet most faults and complaints about high consumption don't originate in the compressor or electronics, but in the installation. Incorrectly sized flow, a poorly placed outdoor unit, a missing hydraulic separator, or an underestimated electrical connection can reduce the real coefficient of performance (COP/SCOP) by 20 to 30% compared to catalogue values. While the unit itself has a lifespan of 15 to 20 years, an installation mistake shows up for that entire time - in higher electricity bills, in noise, in insufficient heating output during frost, or in premature compressor wear. This article summarizes everything to keep in mind when installing a heat pump - from preparation, through positioning the units, the electrical connection, hydraulic wiring, all the way to commissioning and common mistakes worth avoiding.

This article is deliberately advisory and independent of any specific product - at this time we don't have any specific model in stock in the Heat Pumps category, but the information below applies regardless of the brand and type of unit you eventually choose.

Types of heat pumps and their different installation requirements

The first step before any installation is to clarify what type of heat pump is involved, because each has completely different requirements for space, construction work, and permits.

Air-water (split and monobloc): the most widespread type in Slovakia thanks to simple installation without earthworks. It requires a suitable spot on the facade, terrace, or next to the house for the outdoor unit, and for the split version also a refrigerant pipe connection to the indoor unit.
Ground-water (with a horizontal collector): needs a plot with enough area (horizontal collector) or the possibility of drilling vertical boreholes (deep collector) - boreholes generally require notification to the mining authority and a hydrogeological assessment.
Ground-water (with vertical boreholes): the highest upfront investment in earthworks, but the most stable and most energy-efficient source, since ground temperature a few metres deep stays almost constant throughout the year (approx. 8-12 °C).
Water-water: uses groundwater via an intake and infiltration well, requires sufficient water yield and quality, and in many cases also a permit to abstract groundwater from the water management authority.

For the vast majority of family houses in Slovakia today, the air-water variant is used - it's the fastest to install (typically 1-3 days), requires no earthworks or special permits, and today already has comparable efficiency to ground systems thanks to advanced inverter compressors that also work at outdoor temperatures well below freezing.

Preparation before installation: heat loss and correct sizing

The most common mistake still repeatedly seen in the field is estimating the heat pump's output "by eye" or from a simple per-m² rule of thumb. The correct approach is the opposite:

Calculating the building's heat loss - ideally according to standard STN EN 12831, which accounts for the building envelope's construction, window area and type, orientation to the points of the compass, air exchange, and the design indoor temperature in each room.
Choosing the bivalent point - the temperature below which the heat pump alone stops covering the entire heat loss of the house and a supplementary source kicks in (see the section below).
Designing the heating system's temperature spread - the difference between the water temperature at the heat pump's inlet and outlet (typically 5, 7, or 10 K), which directly affects the size of the heating elements needed.
Choosing the unit's output class - with a safety margin generally up to 10%, never oversizing by tens of percent "just to be safe", since this causes frequent compressor switching (so-called cycling), lower efficiency, and faster wear.

Indicative heat consumption of existing family houses in Slovakia in practice falls within these ranges (the actual value is always calculated individually):

Building type	Specific heat loss	Indicative heat pump output for 120 m²
Uninsulated older house (pre-1990)	80-120 W/m²	10-14 kW
Partially insulated house	50-80 W/m²	7-10 kW
House insulated to current standards	30-50 W/m²	4-6 kW
Low-energy / passive house	10-30 W/m²	2-4 kW

We always recommend having the exact calculation done by a designer or an experienced installation company - the simplified estimate in the table above serves only as an initial orientation before a consultation.

Positioning the outdoor unit

For the air-water type, positioning the outdoor unit is one of the most important decisions in the whole project - it affects efficiency, noise, and the unit's lifespan.

Free airflow: the unit draws in a large volume of air (typically 2,000-6,000 m³/h depending on output) and blows the same volume of cooled air back out. If the discharge is blocked by a wall, fence, or other object, the air recirculates back into the intake, the inlet temperature drops, and efficiency deteriorates significantly - this is called a short-circuit (recirculation) flow.

Clearance distances generally recommended in practice (specific values vary by manufacturer and should always be checked against the installation manual):

from the house wall or a neighbouring structure in front (discharge side): at least 100-150 cm of free space;
from a side wall or obstacle: at least 30-50 cm;
from the neighbour's property boundary due to noise: according to a noise study, indicatively 3-5 m for typical outputs for a family house;
above the unit (roof overhang, balcony): sufficient space to avoid recirculation of the warm exhaust air and snow accumulating on the unit.

Noise: modern outdoor units typically reach an acoustic output of 55-65 dB(A) during the day and can quiet down to 45-52 dB(A) in night silent mode. When placed close to a bedroom (your own or a neighbour's), you also need to factor in distance and a possible noise screen - sound decreases with distance from the source by roughly 6 dB with every doubling of distance. Placement directly under a bedroom window or in a corner between two reflective walls (where sound is amplified) is not recommended.

Structure and base: the unit is mounted on a reinforced concrete base, prefabricated feet, or wall-mounted brackets with anti-vibration pads that dampen the transmission of vibration into the house structure. Mounting on a wall next to a living room risks noise transmission through the structure, so a separate ground-level base is generally preferred in practice.

Condensate drainage and ice melt: during the defrost cycle and in rain, condensate drains from the unit and needs to be directed away from footpaths and entrances (risk of ice) - either into stormwater drainage or into a soakaway sloped away from the building.

Indoor unit and utility room

For split systems, an indoor hydraulic unit is installed inside the house (containing the circulation pump, an electric boiler as backup source, an expansion vessel, and controls); for monobloc systems, usually only a smaller distribution unit and a tank are inside. The following principles apply to the utility room:

enough working space around the unit (min. 60-80 cm) for servicing and replacing components;
a floor drain or catch tray in case of a water leak from the system;
the room shouldn't be directly adjacent to a living room because of the operating noise of the circulation pump and any electric boiler;
sufficient ceiling height and access to the electrical distribution board;
if a domestic hot water tank is also part of the setup, you need to allow for its floor footprint (typically 60-80 cm in diameter, 150-190 cm in height for a 200-300 l volume).

Heating system: temperature spread and compatibility with heating elements

A heat pump works most efficiently with a low-temperature heating system - the smaller the difference between the outdoor air temperature (or ground/water temperature) and the heating water temperature, the higher the coefficient of performance (COP). That's why installation always involves assessing whether the existing or planned heating system matches a low-temperature regime.

Type of heating element	Typical temperature spread	Indicative COP at -7 °C outside*
Underfloor heating	30/25 °C to 35/28 °C	3.2-4.0
Low-temperature radiators / fan convectors	45/35 °C	2.8-3.4
Classic (older) radiators, unmodified	55/45 °C and above	2.2-2.8

*Indicative values for a typical inverter air-water heat pump; actual COP depends on the specific model and conditions.

If the house has the original radiator system designed for a high temperature spread (e.g. 70/55 °C for a gas boiler), when installing a heat pump it is generally recommended to take at least one of the following measures: replacing some radiators with larger or low-temperature units with fan assistance, adding underfloor heating in at least some rooms, or hydraulically balancing the system with thermostatic valve heads to achieve the lowest possible real operating spread. Without this consideration, there is a risk that the heat pump will work, but with significantly worse efficiency than stated in the catalogue data sheets.

Electrical connection and required power input

A heat pump is an electrical appliance, and its connection has to be handled by the house's electrical wiring. Designing the connection involves assessing:

Supply: smaller outputs (up to approx. 6-9 kW) are usually single-phase (230 V), larger outputs are generally three-phase (400 V) for a more even grid load and lower starting currents.
Rated current and protection: according to the specific unit's rating plate, typically in the range of 16-32 A per phase including the backup electric boiler; you also need to allow for a type B residual current device (due to the inverter electronics) instead of a standard type A.
Main breaker capacity and reserve in the distribution board: especially in older houses with a 3×25 A main breaker, it's necessary to check with the electricity distributor before installation whether the reserve capacity is sufficient, or to request an increase.
Low tariff (off-peak): many grid operators offer a discounted rate for heat pumps (blocking the high tariff at certain hours) - this requires a separate metering circuit and a ripple control receiver, which needs to be arranged with the electricity supplier before installation.
Lightning protection and surge protection: the outdoor unit, as equipment on the facade/next to the building, should be included in surge protection (a surge arrester in the distribution board).

Bivalent heat source - when it's needed

For air-water systems, the heat pump's output falls as the outdoor temperature drops (less heat is "available" in the air). That's why design involves choosing the so-called bivalent point - the outdoor temperature below which the heat pump alone stops covering 100% of the house's heat loss and a supplementary (bivalent) source kicks in, most often a built-in electric heating element/boiler in the indoor unit.

In practice, for a typical family house in Slovakia the bivalent point is generally chosen between -10 °C and -18 °C, depending on the chosen output class and how many days a year such temperatures actually occur at the given location (a monovalent design for the lowest possible temperature would unnecessarily oversize the unit for the rest of the heating season).

Below the bivalent point, it doesn't necessarily mean "switching" to a different source - the so-called parallel bivalent mode is more common, where the electric boiler adds to (not replaces) the heat pump's output only by the missing difference, so the heat pump keeps running and the supplementary source only covers the peak. As a result, even on the coldest days of the year, the electric boiler contributes only a small part of the total energy delivered over the season (typically under 5%), since extreme frosts make up only a small fraction of the heating hours in a year.

Buffer tank and hydraulic separator

Inverter heat pumps can smoothly modulate their output, but with very low heating water flow (for example when the thermostatic valve heads on most radiators are closed) or when combining several heating circuits with different temperature spreads (e.g. underfloor heating + radiators at the same time), the system generally includes:

Hydraulic separator (low-loss header): separates the heat pump's primary circuit from the secondary heating circuits, prevents them from affecting each other, and protects the heat pump from flow fluctuations.
Buffer (balancing) tank: increases the system's thermal inertia, reduces the number of compressor on/off switches (cycling), and allows smoother operation even at low momentary heat demand. The volume is generally chosen at roughly 10-20 l per kW of heat pump output, with the exact value depending on the type of wiring and the manufacturer's recommendation.
Mixing (weather-compensated) valve on the secondary circuit: if one circuit requires a different temperature than another (e.g. radiators at 45 °C and underfloor heating at 30 °C), a separate mixing circuit with its own pump ensures the correct temperature for each branch.

Controls, weather compensation and post-installation setup

The quality of the controls significantly affects real operating efficiency. The basic elements of a correctly set-up system:

Weather compensation control - the heating water temperature automatically adjusts to the current outdoor temperature according to a set curve, instead of a fixed flow temperature. A correctly set curve is one of the most effective ways to reduce running costs without any construction work.
Room thermostat / room temperature sensor - corrects the weather compensation curve based on the actual temperature in a reference room, and can also enable time programmes (setback at night, comfort during the day).
Domestic hot water preparation control - the schedule for heating the tank (e.g. outside the heating peak or during off-peak tariff hours) and setting the anti-legionella cycle.
Smart control / app - most modern heat pumps offer remote access via a mobile app, which makes it easier to monitor operation, error messages, and consumption.

The initial setting of the weather compensation curve and parameters is usually only indicative - the installation company or service technician usually fine-tunes it during the first heating season based on the house's actual behaviour and feedback from the owner (e.g. "I'm still cold in the mornings" or "we're overheating, the radiators are too hot").

Refrigerant, pressure tests and installer qualification

For split systems (outdoor and indoor units connected by refrigerant pipework, not just water), working with refrigerant is regulated by special rules (so-called F-gas):

installation, brazing of copper pipework, evacuating the circuit and charging refrigerant may only be carried out by a company/technician with a valid certificate under the regulation on fluorinated greenhouse gases;
after connection, the circuit undergoes a nitrogen pressure test (checking joints for leaks) and is then evacuated to remove moisture and air from the pipework - skipping this step is one of the most common causes of later compressor failures;
the amount and type of refrigerant (today most often R32 or R290/propane in some modern models) must match the manufacturer's specified amount for the given pipe length, with additional top-up calculated for longer runs;
for monobloc units (the whole refrigerant circuit is already complete and charged at the factory inside the outdoor unit, with only water running between the units), this restriction doesn't apply - the connection is purely plumbing work, which is one reason for their popularity in renovations.

Even the plumbing and electrical part of the installation itself should be carried out by a professionally qualified person (per the regulation on professional competence in electrical engineering, a licensed trade for installing heating equipment) - this in turn affects the validity of the manufacturer's warranty, which for many brands is conditional on installation by a certified partner.

Installation schedule - how long it takes

An indicative timeframe for a typical air-water installation into an existing house with an existing heating system (without earthworks):

Phase	Indicative duration
Site visit, measurement, design and quote	a few days to 1-2 weeks
Ordering the unit and delivery time	2-8 weeks (depending on model and season)
Installing the outdoor and indoor units, pipework and electrical connection	1-2 days
Pressure test, evacuation, refrigerant charging (for split systems)	half a day to 1 day
Filling and venting the heating circuit, first start-up	half a day
Setting up the controls and training the owner	1-2 hours

When combined with renovating the heating system (e.g. adding underfloor heating, replacing radiators, a new distribution board), the schedule extends by additional days to weeks of construction work. For ground systems (boreholes, horizontal collector), you need to allow additional weeks for earthworks and the necessary permits.

Indicative installation costs

The installation price varies significantly depending on the system type, access to the utility room, the length of the pipe runs, and the scope of related construction work. Indicative cost components (excluding the price of the unit itself):

Air-water split/monobloc installation into a prepared system - the lowest item, including mounting the units, connections, electrical work, and start-up.
Modifications to the heating system (hydraulic balancing, a new buffer tank, mixing circuits) - a medium item, depending on scope.
Upgrading the electrical connection with the distributor, or possibly a new breaker/distribution board - a one-off but not negligible cost, if needed.
Earthworks for ground-water systems (boreholes or horizontal collector) - the highest additional item among all types, potentially making up tens of percent of the total project budget.

An exact quote will always be provided by the installation company after an on-site visit - it depends on local conditions, accessibility, and the scope of work, so we deliberately don't give specific amounts here, which could be misleading outside the context of a specific project.

Commissioning, inspections and documentation

After installation is complete, the customer should receive the following from the installation company:

Commissioning report - generally issued by the manufacturer or an authorised service partner, confirming correct setup and often a condition for the validity of an extended warranty.
Electrical inspection report - mandatory documentation confirming the safety of the unit's connection to the electrical grid.
Refrigerant circuit leak-tightness report (for split systems with a refrigerant charge above the statutory limit), including a record of the amount and type of refrigerant.
Operating manual and service book for the unit, where all subsequent service work is logged.
Training - explaining basic operation, temperature settings, the hot water heating schedule, and what to do if a fault is reported.

We recommend keeping the documentation together with the proof of purchase - it is often needed when making a warranty claim, applying for a subsidy, and when selling the property.

The most common mistakes when installing a heat pump

Underestimated heat loss calculation - output chosen "by eye" or as a flat rate per m² without accounting for the actual state of insulation and windows.
Incorrect placement of the outdoor unit - blocked air discharge, recirculation of cooled air back into the intake, noise directed toward a bedroom or neighbours.
Keeping the original high-temperature radiator system without any modification - the unit works, but with substantially worse efficiency than what is actually achievable.
Omitting a hydraulic separator or buffer tank where their inclusion is required - shows up as frequent compressor switching on and off (cycling), which shortens its lifespan.
Insufficient evacuation of the refrigerant circuit in split systems - residual moisture in the circuit can damage the compressor over time.
An undersized electrical connection chosen without consulting the distributor before installation, which only turns out to be insufficient once the unit is first started up.
An incorrectly set weather compensation curve after start-up - either unnecessarily high (wasting energy) or too low (insufficient comfort, the bivalent source frequently kicking in).
Missing or belatedly addressed frost protection for outdoor pipework and the condensate drain during frost.

Maintenance after installation

Even a correctly installed heat pump needs regular care to maintain its efficiency throughout its lifespan:

regularly cleaning the outdoor unit's evaporator (fins) of dust, pollen, and leaves, which restrict airflow;
checking the free space around the unit, especially before the winter season (clearing snow, removing overgrown vegetation);
checking the pressure in the heating system and topping up water if needed;
an annual service inspection recommended by the manufacturer, generally including checking the refrigerant circuit for leaks, electrical connections, and the controls' functionality;
monitoring error messages via the unit's display or mobile app and addressing deviations promptly instead of ignoring them.

Regular maintenance is also generally a condition for keeping the extended warranty period that many manufacturers offer beyond the statutory warranty.

Frequently Asked Questions (FAQ)

Can a heat pump be installed with the original radiators without replacing them?
Yes, in most cases it can, but efficiency will be lower than with a low-temperature system. Solutions include hydraulically balancing the system, replacing only the least powerful radiators with larger ones or fan-assisted types, and correctly setting the weather compensation curve to achieve the lowest possible real operating spread.

Do I need a building permit to install a heat pump?
For the air-water type in an existing family house, this is generally maintenance work/a change of heating source, which in most cases doesn't require a building permit, though a notification to the building authority may be sufficient - the exact procedure always depends on the local building authority and the scope of related construction work, so it's worth checking in advance. For systems with boreholes (ground-water), the administration is more extensive (notification to the mining authority, a hydrogeological assessment).

How long does the installation itself take?
For a simpler air-water system into a prepared heating system, the installation itself (excluding ordering and delivery of the unit) is usually done in 1 to 2 days. When combined with renovating the distribution or with ground systems, the time extends to days or weeks.

Is the noise of the outdoor unit a problem in a built-up residential area?
Modern units have a noise level in night silent mode comparable to a typical home fridge. With correct placement (sufficient distance from bedroom windows, no reflective surfaces close by) and by keeping the recommended distances from the neighbour's property boundary, noise usually isn't a problem in typical residential areas.

Do I need a backup heat source with a heat pump?
With a correctly designed bivalent point, a modern inverter heat pump can cover the vast majority of the heating season on its own. The supplementary source (most often a built-in electric heating element) serves only as a safeguard for extremely frosty days, which make up only a small fraction of the heating hours in a year, and also as a backup in case of a fault or servicing.

Can a heat pump also be connected to an existing pool or hot water heating?
Yes, several systems allow for simultaneous control of domestic hot water preparation and supplementary pool heating, generally via a separate controlled circuit with its own pump and priority control between heating, hot water, and the pool. The specific option depends on the chosen model and its control unit.

Have a question about heat pump installation?

Dealing with a specific house, an older radiator system, or not sure whether your electrical connection can handle the installation? Write to us - we're happy to help.