Centralized vs. decentralized recovery units – what is better for your home?

When you start designing a mechanical ventilation system with heat recovery, you almost always come across the first crucial question: one large central unit, or several smaller decentralized ones? At first glance, it seems to be a purely technical decision, but in practice, it affects the overall project cost, installation complexity, operating costs, noise level, and comfort for the next twenty years. In this article, we will explore both approaches in depth – with specific numbers, examples from real projects, and without marketing clichés.

Basic principle: how each system works

Before comparing, it is important to understand exactly what each system does. Heat recovery in general means recovering heat from exhaust air – the warm exhaled air transfers heat to the fresh cold air coming from outside, while the two air streams do not physically mix. The efficiency of this process, i.e. the percentage of heat that can be transferred, is a key performance parameter.

Centralized system – one brain for the whole house

A centralized system is based on one heat recovery unit – usually located in a technical room, boiler room, basement, or attic. This unit has its own heat exchanger, a pair of fans (supply and exhaust), filtration sections, and control. A branched ventilation network comes out of the unit – ducts bring fresh air to living rooms and bedrooms, and ducts remove used air from the kitchen, bathrooms, and WC. The air thus travels relatively long distances through the pipes.

The performance of a central unit for a typical family house usually ranges from 150 to 500 m³/h, with a unit of 200–350 m³/h being sufficient for a standard house with an area of 120–180 m². The ducts are either round (flexible pipe with a diameter of 75, 90 or 125 mm, led in a star pattern from a distribution box), or classic rectangular ducts.

Decentralized system – each room on its own

The decentralized approach places small units directly into the wall of each room (or one for every two rooms in paired arrangements). Each unit has its own small fan, a ceramic or plastic heat recovery accumulator, and is directly connected to the outside through an opening in the wall with a diameter of typically 160 mm. No internal piping, no air ducts between rooms.

These devices usually work in pairs (master + slave) or in synchronized groups: while one unit blows air in, the adjacent one blows air out, and after several tens of seconds the direction is reversed. Heat is stored in the ceramic filling of the heat exchanger and transferred during the opposite cycle. A typical decentralized ventilation unit HRC E – electronic version Master with a diameter of 160 mm can handle spaces from 15 to 40 m² and operates with a noise level typically below 35 dB(A) at medium performance.

Comparison of systems from the perspective of installation and construction interventions

This is one of the most important differences, which in practice decides the choice more than any technical parameter. Installation of a centralized system is a large construction project – it requires the realization of the entire ventilation network, which means drilling, milling grooves or routing pipes in drywall partitions, underfloor spaces and technical shafts. In practice, it is practically impossible to install a centralized system into an existing inhabited house without significant interventions.

On the other hand, decentralized units require only a hole in the wall – with a diameter of 160 mm, it is one drilling with a core drill, which an experienced mason can do even without special equipment. The entire installation of one room including electrical connection takes two to four hours. This is a crucial advantage in renovations, in houses with thick walls or in situations where you do not want to damage the plaster.

With a centralized system, distribution boxes are also necessary – so-called modular distribution cabinets to which individual branches of the distribution are connected. An example of typical accessories is connector for modular distribution cabinet for IVAR.PROFI-AIR CLASSIC (ex. 90 mm), which allows the assembly and extension of distribution sections. Proper dimensioning and arrangement of these elements requires an experienced designer – errors in the distribution are very difficult to correct later.

With a decentralized system, the quality of the external termination is also important. External aesthetic grid for IVAR.HRC diameter 160 mm is not just an aesthetic accessory – a properly shaped grid prevents the entry of insects, leaves and prevents backdraft of air when the unit is turned off. I always insist on using a quality solution on the outside, not a generic flat grid from the hardware store.

Energy efficiency – where are the real differences?

On paper, centralized systems look better – modern counterflow heat exchangers achieve heat recovery efficiency of 80 to 92 %, while the rotary ceramic heat exchangers in decentralized units typically range between 70 and 85 %. Theoretically, therefore, a centralized unit is more energy efficient.

Reality is more complicated, however. With a centralized system, you have to subtract the heat losses of the long distribution – air traveling several meters through pipes across a cold attic or technical room loses heat. If the pipes are not sufficiently insulated (and in practice they often are not), the real system efficiency drops to 65–75 %. In addition, the larger fan of the central unit consumes more electrical energy – typically 50 to 150 W during normal operation.

Decentralized units have a shorter thermal path – air passes through the ceramic accumulator directly into the room, and losses are minimal. The electrical power of a unit for one room is 3–8 W, for a whole house with eight units it is 24–64 W. If we take both components into account, in well-designed and implemented installations, the energy differences between the systems are smaller than they seem at first glance.

Investment and operating costs – the real picture

Comparing prices is a sensitive topic, as it depends on the specific project, house layout and local market. Despite this, characteristic patterns can be identified.

Centralized system – cost calculation

The central unit itself for a family house with a capacity of 300 m³/h typically costs from 1,500 to 4,000 euros, depending on the brand and equipment. In addition, you need to add material for the distribution – pipes, distributors, bends, insulation, grilles, valves – which for a 150 m² house costs another 800 to 1,800 euros. Installation of ventilation is a skilled job and reliable companies charge 60–90 euros/hour; the total installation including regulation and commissioning can easily reach 2,000 to 4,000 euros. Total investment costs for a new build thus range from 4,000 to 10,000 euros, and even more in complicated installations.

Decentralized system – cost calculation

For a 150 m² house, you typically need 6 to 10 decentralized units (depending on the layout and room sizes). The price of one unit ranges from 250 to 600 euros. Installation is significantly simpler – with an experienced two- or three-person team, you can fit out the whole house in one day. Total investment costs are thus typically 2,500 to 6,000 euros, i.e. 30–50 % lower than with a centralized system.

Operating costs are also lower with a decentralized system – the filter is cleaned on each unit separately and it is a simple operation without special tools. The heat recovery inserts are removed and cleaned as needed, usually once every 3–6 months, which we will describe in more detail in the article Maintenance and cleaning of heat recovery inserts – how often and how properly. With a centralized system, service is more technically demanding – you need access to the unit, the filter is larger, and replacement of the heat recovery block is more expensive.

Noise – where and who is it disturbing?

One of the most common complaints about central systems is noise. The central unit produces vibrations and noise that can spread through the piping throughout the entire house. If the unit is not properly anti-vibration mounted, if the piping is not separated by rubber inserts, and if the ducts are not properly dimensioned (air speed over 2.5 m/s in the duct generates flow noise), the result can be unpleasant. In practice, we have resolved several complaints where the central unit in the basement caused a buzzing resonant sound in the bedroom upstairs – a problem that required a complete reprofiling of the unit's mounting.

Decentralized units have small fans directly in the wall of the room, which sounds paradoxical – yet in practice, they are quieter because the small motor generates significantly fewer vibrations and there is nothing to spread through the piping. Quality units operate at medium performance at 25–32 dB(A) – that is quieter than a whisper. A problem can be the frequency tone of the motor and the switching sound when changing direction (every 70–90 seconds), but modern electronic versions with EC motors eliminate this effect through smooth regulation. More on this topic can be found in the article Noise from heat recovery units – causes and solutions.

Flexibility and the possibility of phased implementation

Here, the decentralized system has a clear advantage. You can start with one or two units in the bedroom and children's room – that is, where air quality at night is most important – and gradually add more. With a central system, you have to implement the entire duct network at once, otherwise it makes no sense.

This flexibility is also the reason why decentralized units are popular in apartment and row house renovations, where each room is renovated separately. We have seen customers who gradually equipped their entire apartment with six units over three years, adding each one during the renovation of the respective room. Such an approach is practically unthinkable with a central system.

Flexibility is also evident when changing the layout – when a children's room becomes an office and the way spaces are used changes, the setting of a decentralized unit can be easily adjusted directly on site. A central system requires reprogramming the controller and possibly adjusting the balance of the entire network.

Where the central system truly excels

It would be unfair to only criticize the central unit – in the right conditions, a central system is clearly a better choice.

• Large houses over 200 m²: With a larger floor area, the number of required decentralized units increases significantly, investment costs rise, and coordinating the synchronization of many units becomes complicated. A central unit can handle the entire house simply and elegantly.
• Requirement for central filtration: For allergies, asthma, or in areas with high dust levels, it is advantageous to have one high-performance filter (e.g., H13 HEPA) for the entire house. A central unit makes this easy, while decentralized units are limited by the size and available space in the unit.
• Integration with air conditioning or heat pump: A central ventilation network allows not only fresh air distribution but also cooling or reheating – this is practically impossible with decentralized units.
• Passive house or low-energy standard: Here, the designer is required to achieve high system efficiency, and a central counterflow unit with over 90% efficiency provides more room to meet the standard requirements.
• Single central control: With a central system, you control the entire house from one control panel or mobile app – it is more convenient than manually adjusting each decentralized unit separately (although modern systems allow centralized control of decentralized units via communication protocols).

Where the decentralized system clearly wins

• Renovation of an occupied building: The strongest argument by far. There is no need to tear down plaster, create shafts, or disturb the existing layout.
• Apartment buildings and apartments: Each apartment is autonomous, and no coordination with the building manager or other owners is needed.
• Phased implementation: Ideal for gradually equipping a house according to financial possibilities.
• Smaller houses and cottages: For spaces up to 120–150 m², a decentralized system is more cost- and logistically advantageous.
• Low noise: When absolute night quiet in bedrooms is a priority, modern decentralized units are hard to beat.
• Simple maintenance without a professional: A regular user can easily clean the filter and ceramic insert without the help of a service technician.

Technical details – pipe diameters and seals

For those interested in a deeper technical view, we provide a few notes on sealing and connecting components, which are key to safety and efficiency in both systems.

In decentralized units, the tightness of the connection with the wall opening is critically important – any leakage at the interface between the unit and the building opening causes thermal bridges, condensation, and worsens acoustics. A high-quality 63 mm diameter tongue-and-groove seal for the Classic system is an example of a solution where flexible tongues copy the irregularities of the inner surface of the opening and at the same time allow for easy installation and removal without tools.

In a centralized system, we regularly encounter the need to amplify the control signal or increase the air volume in distant branches. For this purpose, auxiliary components such as amplifier for diameters 75 or 90 mm can be inserted into the ducting where pressure loss on a long branch causes insufficient flow. Proper balancing of the system is one of the most demanding phases of installation of a centralized system in practice – we deal with it in detail in the article How to properly design a ventilation system with heat recovery.

Regarding pipe diameters: in centralized systems with a star layout, the most commonly used ducts are 75 mm in diameter (for individual rooms) and 90 mm (for main branch collectors). The main pipe between the unit and the distributor has a diameter of 160 to 250 mm. Detailed information on dimensioning can be found in the article What pipe diameter do I need for heat recovery ventilation.

Combined solutions – hybrid approach

In practice, nothing is black or white. Some projects use a hybrid approach – a central unit serves common areas and main rooms, while some distant rooms or additions are handled in a decentralized way. Such a solution is more complex in terms of project planning (it requires coordination of two systems), but it can be optimal in the renovation of a larger house, where the centralized system was installed during the original construction and the new addition is handled in a decentralized way.

Another combination is the use of a central unit for ventilation and at the same time adding decentralized units in rooms with higher humidity (bathroom, laundry room), where local extraction of moist air is more advantageous than relying solely on central exhaust.

Practical examples of customer projects from experience

Example 1: Single-family house in a new build, 180 m², passive standard

The investor wanted a low-energy house with certification. We chose a centralized counterflow unit with 91% heat recovery efficiency, an integrated bypass for summer night cooling, and HEPA filtration due to a family member's allergy to pollen. The ducting was implemented as a star layout in the floor structure during the rough construction phase. Total investment: 8,200 euros including installation. After starting the system, it has been running smoothly, the system's electricity consumption is 65 W in normal operation, which corresponds to three light bulbs.

Example 2: Brick apartment building, apartment 85 m², renovation

Third-floor apartment, thick brick walls, neighbors above and below. A centralized system was ruled out from the start – concrete in the ceiling, wires in the walls, no technical room. We designed five decentralized HRC units with a diameter of 160 mm, two of which were paired and synchronized in the bedroom and children's room, and three individual units in the living room and study. Installation took two days, and the opening work (drilling) took one day. The client was satisfied, especially because he could live normally during the installation and the apartment remained livable. Total costs: 3,600 euros.

Example 3: Cabin 60 m², insufficient ventilation, asthma

The cabin owner suffered from asthma and had to ventilate by opening the window every hour, which was unbearable in winter. Two pairs of decentralized units (four units in total) solved the situation in less than a day of installation. Ceramic heat recovery preserves heat, and the air is filtered through a fine filter. Result: subjectively much better air quality, heating costs decreased because heat was not lost by window ventilation. Cost of the solution: 1,800 euros.

Legislation, standards and energy certificate

In Slovakia, mechanical ventilation with heat recovery is gaining prominence in connection with the building energy performance certificate (EPC). STN EN 15251 defines classes of indoor air quality, STN EN 13779 deals with performance criteria for ventilation systems. For passive houses, the requirement for minimum heat recovery efficiency according to the criteria of the Passivhaus Institute (PHI) applies, where efficiency must be over 75% and specific electrical consumption (SFP) must be under 0.45 Wh/m³.

An interesting fact is that in the calculation model of the energy certificate, decentralized systems are sometimes rated worse due to the lower nominal efficiency of the heat exchanger, although real operation can be energy-wise comparable or better. This is an area where it is advisable to consult with an energy certifier before choosing a system, so you know what impact the technology choice has on the final energy label of the house.

Most common mistakes when choosing a system

Over the years of practice, we have seen these recurring mistakes:

• Underestimating the building preparation: A customer orders a centralized system, but during implementation it turns out that there is no space in the ceiling for ducting and the renovation would cost more than the entire system. Always start with a building survey, not with the selection of the unit.
• Overdimensioning decentralized units: More does not mean better. An overly powerful unit in a small room causes drafts and unnecessary noise.
• Neglecting thermal insulation of ducts: In a centralized system, insulation of pipes running through unheated areas is often neglected – the result is a drastic drop in real efficiency.
• Incorrect synchronization of decentralized units: If units in adjacent rooms blow in the same direction at the same time (both in or both out), pressure problems occur. Correct synchronization is technically simple, but must be checked during commissioning.
• Ignoring the location of the external outlet: The air outlet on the façade must not point to a corner, under an overhanging part of the roof, or near window openings – otherwise, reverse circulation occurs. More on this topic in the article Rooftop vs. façade outlets for heat recovery – which to choose and when.

Most frequently asked questions (FAQ)

Can I install decentralized units myself, without a professional?

Basic installation – drilling a hole, mounting the housing, inserting the unit – is technically accessible to a skilled DIY enthusiast. The more critical part is the electrical part: the unit requires connection to 230 V and, in the case of paired or group installations, also correct connection of control wires for synchronization. If you do not have experience with electrical installation, we recommend leaving the electrical connection to an electrician. A detailed procedure can be found in the article Installation of a decentralized ventilation unit HRC step by step.

How many decentralized units do I need for a 130 m² house?

A general rule says one unit for every 20–35 m² of living area, depending on the layout and the performance of the specific unit. For a 130 m² house with a standard layout (four rooms, two bathrooms, kitchen, living room), plan for 5 to 8 units. The exact calculation is based on the hygienic minimum air exchange: 25–30 m³/h per person in the bedroom, 40–60 m³/h in the living room and study.

Is a centralized system suitable for the renovation of an older house?

Technically yes, but in practice it is very demanding and expensive. Implementation of ducting in an existing house requires either cutting grooves and subsequent plastering, or the construction of drywall false walls and soffits, which fundamentally changes the interior appearance. In many cases, the total cost of renovation with a centralized system is two to three times higher than with a decentralized solution, and the result is not always better. An exception is when the house is completely renovated down to the "rough construction" stage.

How do decentralized units handle moisture condensation?

Ceramic heat recovery units in decentralized systems have minimal issues with condensation when properly sized and set up – the ceramic absorbs moisture during exhaust and releases it back during supply air, effectively transferring moisture (latent heat) as well. In extreme cold below –10 °C, freezing may occur on the outer side of the casing, but modern electronic controls (such as in the HRC E electronic version Master unit) automatically activate defrost cycles. In centralized systems, condensate is drained from the unit via a hose – it is necessary to connect it to a sewer or condensate tray.

What happens if the central unit fails?

This is one of the underestimated risk factors of a centralized system. In the event of a failure, ventilation for the entire house stops – no room, no space. In winter, without ventilation, humidity and CO₂ concentration quickly rise. A service technician and spare parts must arrive promptly. In a decentralized system, a failure of one unit does not affect the others – the house remains ventilated, only one room temporarily operates passively. This aspect of redundancy is an important argument in favor of decentralization when assessing long-term operational reliability. For information on common faults and their solutions, see the article Common faults of heat recovery units and how to resolve them.

Is it possible to connect a decentralized system to "smart home" control?

Modern electronic versions of decentralized units (such as HRC E) support communication via RS-485, Modbus or proprietary protocols. Connection to KNX, Loxone or Home Assistant systems is technically possible via appropriate gateways, although it requires professional setup. Centralized systems traditionally offer broader support in this area, as suppliers provide complete control systems with touchscreens, mobile apps, and integration with weather stations. If smart home integration is your priority, check the supported protocols of a specific model before purchase.

Conclusion: there is no clear winner

After reading the whole article, you have probably understood why the question "what is better" has no simple answer. Both systems have a solid place on the market and both are excellent solutions when applied correctly.

A centralized system is optimal for new construction of larger houses, passive houses, cases with HEPA filtration requirements, and integrated HVAC control. A decentralized system excels in renovations, apartment buildings, smaller spaces, phased implementation, and anywhere there is no space or willingness to perform major construction work.

If you are at the beginning of the decision-making process, we recommend starting with a detailed analysis of the building condition, layout, and your own priorities (cost, noise, filtration, flexibility). More general information on system selection can be found in the article How to choose a mechanical ventilation system with heat recovery for a family house and for more common questions also in Frequently asked questions about mechanical ventilation with heat recovery. The right choice made at the beginning of the project will save you years of frustration and thousands of euros in unnecessary costs.

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