Step-by-step installation of decentralized HRC ventilation unit

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Step-by-step installation of a decentralized ventilation unit HRC

Decentralized ventilation units with heat recovery are among the most popular solutions for ventilating single-family homes, apartments, and offices today. Unlike central systems, they do not require extensive ducting running through the entire building – each unit is responsible for ventilating one room separately, while recovering heat from the exhaust air. The result? Fresh air, minimal heat loss, and relatively simple installation.

Despite the fact that installation may seem simple at first glance – "drill a hole, plug it in, wire it up" – in practice, installation errors can manifest for many years ahead: condensation dripping down the wall, noise, insufficient heat recovery, or premature wear of the device. In this article, we will go through the entire process from measuring and preparation through drilling the core hole, inserting the sleeve, installing the unit, to electrical connection, startup, and adjustment. We emphasize the details that most installation manuals skip.

If you are still considering whether a decentralized system is the right choice for you, we recommend reading the article Centralized vs. decentralized heat recovery units – what is better in our Knowledge Center first. If you have already decided, read on.

What is a decentralized HRC unit and how it works

HRC (Heat Recovery Controller / Heat Recovery Cell) is a compact unit built directly into the perimeter wall. In most versions, it operates on the principle of periodic air flow direction switching – for several minutes it exhausts air outside and heats the ceramic heat recovery insert, then reverses the direction and the same insert preheats the incoming fresh air. This cyclic principle achieves a heat recovery efficiency of 75–92%, which is comparable to high-quality central systems.

A typical representative of this category is, for example, the decentralized ventilation unit HRC E – electronic version – 05 Master; pr. 160 mm. Its dimensions of 180 × 180 × 540 mm and weight of 4.0 kg are typical for this class of devices – the device is relatively long, which is related to the wall depth and the length of the heat recovery insert. The diameter of 160 mm determines the diameter of the core hole that needs to be drilled.

The unit is mounted into a wall sleeve that passes through the entire wall thickness. On the exterior side, a protective grid is mounted (e.g., external aesthetic grid for IVAR.HRC – pr. 160 mm), and on the interior side, an aesthetic cover with a filter and control elements.

What you need before starting the installation

Tools and materials

Core drill bit (corona) – diameter 2–3 mm larger than the outer diameter of the sleeve (for HRC with a diameter of 160 mm, usually a corona ø163–165 mm)
Drill or hammer drill with sufficient power (minimum 1,500 W for a concrete wall, ideally diamond core drilling for thick walls)
Water level, laser level, or cross laser level
Tape measure, pencil, string
Shoe for measuring wall thickness
Hammer and chisel (for possible reinforcement or hole adjustment)
Sealant (PUR foam) for sealing and fixing purposes, sealant, plaster patch
Screwdriver, sheet metal shears (or grinding disc)
Extension cord and circuit breaker
Detection device for reinforcement and wiring in the wall (so-called stud finder / metal detector)

Construction materials

Wall sleeve (usually part of the unit package or delivered separately)
Mineral wool or PUR foam for filling the gap between the sleeve and the wall
Vapor barrier tape (mandatory in passive houses and low-energy buildings)
Sealant for final sealing of the openings on both sides

Documentation and preparation

Before drilling, check the building's project documentation or have the wall scanned by a professional. In panel buildings, reinforcement steel may pass through the wall, while in the wall of an old brick house, there may be an old installation. This saves nerves and money. At the same time, check where the nearest electrical outlet is – the HRC E unit is electrical and requires 230 V / 50 Hz power supply.

Choosing the right location for installation

The location of the unit in the room significantly affects its efficiency and comfort. A few basic rules that an experienced installer never skips:

Installation height

The optimal height of the center of the opening is 1.7–2.0 m above the floor. A unit installed too low blows cold external air directly onto the occupants of the room during the air intake phase – which is uncomfortable and can cause health problems. A unit installed too high (e.g., right under the ceiling) reduces the efficiency of air mixing in the room. For kitchens, many installers recommend a height of 1.8–1.9 m, while for living rooms you can go a bit higher.

Position in the wall

The unit must be installed in a perimeter wall facing directly outside. Never install it in an internal load-bearing wall (it doesn't make sense), or in a wall behind an unheated basement or garage – this could lead to unwanted cold air infiltration or condensation for other reasons. If there is a radiator on this wall, consider placing the unit above it – the heated air from the radiator will help with the distribution of fresh air.

What should not be done

Do not drill a hole in the corner of the room (less than 30 cm from the corner) – air distribution deteriorates and acoustic problems arise
Do not drill into a load-bearing structure without a static assessment
Do not forget the minimum distance from the window (at least 50 cm) – otherwise, air flow short-circuiting occurs and the air that has just arrived immediately goes back out
Avoid locations behind furniture or hidden behind a wardrobe

Core drilling – the most important step of the entire installation

Core drilling is the heart of the entire installation. It is done once and mostly permanently – repairing a poorly drilled hole is laborious and expensive. That is why it pays to be thorough.

Measuring and marking the hole

Mark the center of the future hole on the wall. Use a spirit level or a laser level to check that the point is truly in a horizontal plane – the HRC unit must be horizontally level or slightly (0.5–1°) sloped outward. This small outward slope is critically important: it prevents condensate water from dripping into the room.

The slope may seem negligible, but in practice we have seen dozens of cases where the installer did not pay attention to this detail and the owner had to deal with moisture on the interior wall or even a leaking facade from the inside. The rule is simple: for a wall thickness of 400 mm, it is sufficient to shift the exterior side 4–6 mm lower than the interior side (for a slope of about 0.5–1°).

Drilling itself

For brick masonry, a standard percussion drill with a 163 mm diameter core bit is sufficient. For reinforced concrete (panel houses, monolithic structures), we recommend ordering diamond core drilling – a specialized company or a rented set. Diamond drilling is more expensive, but cleaner, without vibrations and without the risk of damaging the reinforcement on impact.

Drill from the interior towards the exterior, not the other way around. The reason is practical: when the last layer is pierced, a breakout occurs on the exit side – interior cleaning is simpler and more aesthetically unobtrusive than exterior cleaning. In addition, you have better control over the slope of the hole.

Wall thickness also affects the length of the sleeve – check before ordering whether the supplied sleeve covers the entire thickness. Standard 160 mm HRC units are supplied with a sleeve length of 310–540 mm. For thicker walls (e.g. RC + insulation), an extension may be required.

Cleaning the hole

After drilling, thoroughly clean the hole of dust and debris. Check that the diameter is uniform along the entire length – with bricks, it sometimes happens that the core bit "drops" by a few millimeters. Reinforce the edges of the hole with a plaster patch or a bridging sealant to prevent the wall around the hole from crumbling.

Installing the wall sleeve

The wall sleeve is a plastic or aluminum pipe that passes through the entire wall thickness and protects it from mechanical damage and moisture. Proper installation of the sleeve is a prerequisite for the long life of the system.

Installation procedure

Insert the sleeve into the hole from the interior. Before inserting, wrap it with mineral wool or PUR tape of about 3–4 cm width around the entire perimeter – this layer of thermal insulation prevents the formation of a thermal bridge and condensation on the surface of the sleeve in the interior. In low-energy and passive houses, it is also mandatory to wrap the sleeve with a vapor barrier tape and directly adhere the excess tape to the vapor barrier in the wall.

After inserting the sleeve, check with a spirit level that it has the correct slope (see above). The gap between the sleeve and the wall (the remainder from the drilling) is filled with low-expansion PUR foam – not standard window mounting foam, as it expands too much and may deform the thin-walled plastic sleeve. After the foam has hardened, cut off the excess and apply a layer of sealant with a brush.

On the exterior end of the sleeve, install a protective exterior grid. We recommend an aesthetic solution – for example, exterior aesthetic grid for IVAR.HRC – e.g. 160 mm – which both aesthetically covers the opening and prevents the entry of insects, birds and larger debris. The grid is usually attached with screws or snaps into the sleeve.

Installation of the HRC unit itself

Once the sleeve is mounted, sealed, and fully cured (PUR foam typically requires at least 24 hours), you can proceed with the installation of the ventilation unit itself.

Preparing the unit before inserting

Before inserting, check the ceramic recovery insert – it should be dry, clean, and undamaged. If the device has been stored for a longer period, also inspect the fan module. Make sure all seals (rubber rings, tongue-and-groove seals) are in place. For proper sealing of the connection between the sleeve and the unit body, special tongue-and-groove circular seals are used – these ensure that air flows only in the controlled direction through the recovery insert and not through gaps around the unit body.

Inserting the unit into the sleeve

Insert the unit into the sleeve from the interior side. Make sure it does not get stuck or twist – most HRC units have directional markings on the body (e.g., an arrow pointing upwards), so you can insert it in the correct position for the proper operation of the fan and condensate drainage. The unit should be held in place by friction and pressed against the interior cover.

The interior front panel (cover with filter) is attached to the wall around the opening using screws. Make sure the cover fits tightly against the wall all around – otherwise, air will leak around the frame instead of passing through the filter. In the case of an uneven wall (e.g., stucco), use sealing compound under the frame of the cover.

Systems with multiple units and boosters

In larger installations or in larger rooms (over 30–35 m²), sometimes two HRC units are used in one room. If the system requires connection to a central duct or coordination of multiple channels, it is necessary to use appropriate connecting components – for example, booster – e.g. 75 mm or 90 mm; classic, which allows increasing air flow in the system without excessive noise. For modular ducting, components such as connector for modular distribution box – e.g. 90 mm; classic are used.

Electrical connection and configuration

HRC E units (electronic version) require connection to 230 V / 50 Hz. This is a point where many DIY enthusiasts struggle, and we recommend calling an electrician – at least for the actual electrical installation.

Requirements for the electrical connection

Power supply 230 V AC, 50 Hz, power consumption depends on the model (typically 3–18 W during operation, max. 25–35 W at full power)
Recommended protection: 10 A type B circuit breaker, surge protector
Supply cable min. 3×1.5 mm² (CYKY or equivalent), protected in a cable tray or in-wall
Socket or fixed supply behind the cover – some units have a connector, others have a direct cable

Setting up the control electronics

The electronic version HRC E 05 Master has a built-in control module, which allows:

Setting the direction change interval (typically 60–90 s)
Setting the ventilation intensity – usually 3 levels (30/50/80 m³/h)
Connecting to an external hygrostat or CO₂ sensor (for more advanced installations)
Linking between two paired units (for larger rooms) – paired units alternate direction synchronously, which eliminates the problem of short-term flow of cold air

Settings are usually done via DIP switches on the control board or via an app (if the unit has a WiFi module). Details can always be found in the installation manual of the specific unit.

First start-up – what to check

After completing the installation and electrical connection, the first start-up follows. We recommend doing this systematically and not immediately expecting maximum performance:

Visual inspection: Check that all covers are in place, the filter is correctly inserted, and the external grid is properly secured.
First switch-on at the lowest level: Turn on the unit at the lowest performance (e.g. 30 m³/h) and listen – the fan should run quietly without vibrations. Any squeaking, clanking, or uneven operation indicates a problem with the bearing or foreign object in the duct.
Airflow check: Place your hand near the interior grid and check that you feel airflow. In one phase of the cycle, you should feel suction (air going out), in the other phase supply (air coming in). The cycle typically lasts 60–90 seconds.
Exterior check: Go outside and place your hand (or a piece of paper) near the external grid. Check that the airflow corresponds to the interior phase.
Recovery temperature measurement: In cold weather (e.g. +5 °C outside, +21 °C inside), the incoming air at the room entrance should be significantly warmer than the outside air – at least +14 to +17 °C, which corresponds to a recovery efficiency of 75–85 %.
Condensate: In cold weather and with humid interior air, condensate may form in the sleeve. After 24 hours of operation, check that the condensate drains outside and does not drip into the interior.

Typical problems during installation and how to avoid them

Over the years of practice we repeatedly encounter several mistakes that we would like to avoid:

Insufficient slope of the sleeve

By far the most common problem. The sleeve is horizontal or even slightly sloped inward. Result: condensate runs down the inner wall, mold and a wet stain appear at the edge of the cover. A solution in a finished wall is very unpleasant – the unit must be removed, the sleeve disassembled and reinstalled. Therefore, invest enough time in the correct slope before embedding.

Incorrect insulation of the sleeve

If the sleeve is not insulated around its perimeter with mineral wool or PUR tape, a thermal bridge is created. In winter, the sleeve cools down and moisture from the air condenses on its surface inside. After years, this leads to damage to the plaster and mold on the wall around the cover.

Missing sealing gasket

If the unit is not properly sealed in the sleeve, air "short-circuits" – it flows around the body of the unit rather than through the heat recovery insert. Result: low heat recovery efficiency, cold draughts, increased noise. Check the condition of the seals during every disassembly for cleaning.

Forgetting the filter

The frame of the interior cover contains an air filter (usually class G3 or G4). This filter must be replaced or cleaned regularly – every 3–4 months under normal pollution conditions, and monthly in higher pollution conditions (near a road, during pollen season). A dirty filter dramatically reduces air flow, increases noise and shortens the life of the fan. More on this topic can be found in the article Maintenance and cleaning of heat recovery inserts – how often and how to do it properly in our Knowledge Center.

Incorrect position – short-circuit airflow

A unit installed too close to a window or in a room corner has a problem with short-circuit airflow: fresh air that has just entered is immediately drawn back out without mixing properly with the air in the room. Result: reduced air quality despite the unit running. Always maintain a minimum distance of 50 cm from windows and 30 cm from corners.

Maintenance after installation – what and when

A decentralized HRC unit is an almost maintenance-free device, but "almost" does not mean "none". Regular maintenance prolongs the life of the device and keeps its performance at the declared level.

Every 1–3 months: Visual inspection and cleaning of the interior filter (vacuum cleaner, possibly washing in lukewarm water and drying)
Every 6 months: Removal and inspection of the heat recovery insert – must not be wet, dirty or cracked
Once a year: Inspection of the exterior grille – remove leaves, insects, spider webs; check the condition of the grille seal
Every 2–3 years: Inspection of the sleeve and seals, check the mounting of the cover and grille; if the device is exposed to hard water (condensate), clean it of limescale

The topic of faults and their solutions is also covered in a separate article Common faults of heat recovery units and how to eliminate them in this Knowledge Center.

Specific situations and practical recommendations

Installation in an insulated house (ETICS)

In houses with wall insulation (external thermal insulation composite system ETICS), installation is more complicated. The wall thickness increases by the thickness of the insulation (EPS, mineral wool, PUR boards), so the total sleeve length can reach 500–600 mm or more. Key points are:

Use an extension sleeve of the correct length
Mount the exterior grille so that it protrudes at least 30 mm from the surface of the insulation (to prevent rainwater from seeping into the insulation)
Seal the junction between the grille and the insulation with vapor-tight sealant resistant to UV
If the insulation was installed later (renovation), always drill a new hole through the insulation using a drill of sufficient length

Installation in old houses with thick walls

Old rural houses, stone or brick houses from the 1940s may have walls of 60–80 cm thickness. For such cases, special extended sleeves and adapters are available. Drilling is more demanding – usually a diamond drill is required. The slope is even more important here, as a longer sleeve can collect more condensate.

Installation in a multi-story apartment building

In apartment buildings, you must obtain approval from the building manager or apartment association before installation. An external intervention in the façade requires approval. In addition, you must consider how the exterior grille will look in the context of other elements on the façade. In some apartment buildings, there is a shared ventilation shaft – in such cases, HRC is not applicable and ventilation must be solved in another way (see the article How to choose a mechanical ventilation system with heat recovery for a single-family house in the Knowledge Center).

Noise

Decentralized HRC units are very quiet under normal conditions – typical noise level is 20–35 dB(A) at medium performance, which is less than a whisper. If the unit is noisy, the cause is almost always in the installation: unbalanced fan (foreign object), vibration of the cover against the wall (missing sealing strip under the frame), sleeve resonance. More on this topic: article Noise from heat recovery units – causes and solutions in the Knowledge Center.

Most frequently asked questions (FAQ)

Can I install an HRC unit myself, or do I need a professional?

The construction part (drilling, installing the sleeve) can be handled by a skilled DIY enthusiast with the right tools. The electrical connection must be done by a licensed electrician – otherwise you may have problems with insurance and warranty of the device. We recommend a final inspection of the entire installation by a professional in the field of HVAC.

How long does the installation of one unit take?

With preparation and professional diamond drilling, it takes about 2–4 hours per unit including waiting time for the curing of the PUR foam (which hardens in 30–60 minutes). If you include masonry finishing and painting, you should count an additional day of work. Installation of a full system for a 3-room apartment (4–6 units) takes an experienced team 1.5–2 working days.

What is the optimal drill bit diameter for HRC with a diameter of 160 mm?

The outer diameter of the sleeve for HRC 160 mm is usually 165–168 mm (depending on the manufacturer). The bit should be 1–3 mm larger, typically ø168–170 mm. A too large gap (more than 5 mm) is unnecessary and complicates sealing; a too small gap (less than 1 mm) may prevent the sleeve from being inserted. Always check the dimensions in the technical documentation of the specific unit.

What to do if there is no exterior wall in the room?

This is a situation that occurs in practice, for example, in central rooms of an apartment or in a bathroom without a window. In such a case, it is not possible to install a decentralized HRC unit and a central ventilation system with ducting must be used. More information can be found in the article How to properly design a ventilation system with heat recovery and in the category mechanical ventilation with heat recovery.

How long does a ceramic heat recovery insert last?

High-quality ceramic inserts have a lifespan of 10–15 years with proper maintenance. Their lifespan is reduced by mechanical damage (e.g., careless disassembly), grease contamination (so HRC is not suitable for the kitchen without a special grease filter), and extreme conditions (strong frost below -15 °C causes condensate to freeze in the insert). In such cases, the unit automatically switches to a protective mode – more in the article Common faults of heat recovery units and how to eliminate them.

Is it possible to connect HRC to a central control of a smart home?

Depends on the model. Electronic versions of HRC E usually have outputs for external control (relay, 0–10 V input) and some have a WiFi module for direct connection to KNX, Modbus or proprietary applications. When planning smart home integration, always check the compatibility of the specific model with your control system before purchase.

Conclusion

Installation of a decentralised ventilation unit HRC is not rocket science, but it is a craft that requires precision, patience and thorough preparation. The key points that determine the success or failure of the entire installation are the correctly selected and marked installation location, precisely drilled and properly angled hole, thorough thermal and airtight insulation of the sleeve, and correct electrical connection. If you master these points perfectly, you will enjoy a device that brings you fresh air year after year, saves energy and practically requires no maintenance.

To choose the right accessories, spare parts and add-ons for your HRC unit, go to the mechanical ventilation with heat recovery category on atria.sk, where you will find a complete range including external grilles, seals, boosters and other accessories.

Do you have a question about this topic?

Having trouble making a decision or dealing with a specific situation in your home? Write to us – we are happy to help.