Central MVHR vs Decentralised Units Compared

A home can look freshly decorated yet still suffer from streaming windows, musty bedrooms and mould returning around cold corners. When comparing central MVHR vs decentralised units, the right answer is not simply the system with the highest headline efficiency. It is the system that can be properly designed, installed, commissioned and maintained for the building in front of you.

Mechanical ventilation with heat recovery, or MVHR, removes stale, moisture-laden air while supplying filtered fresh air. The heat from the extracted air is transferred to the incoming air through a heat exchanger, helping to reduce heat loss compared with opening windows alone. Both central and decentralised approaches can improve indoor air quality, but they do so in very different ways.

What is central MVHR?

A central MVHR system uses one main heat recovery unit, usually located in a utility room, attic or service cupboard. Ductwork runs from the unit to the rooms that need fresh-air supply, typically bedrooms and living spaces, and to wet rooms such as kitchens, bathrooms and en-suites where stale air is extracted.

The system works continuously at a low background rate. Air moves through the home in a planned direction: fresh air enters habitable rooms, passes through transfer paths such as undercut internal doors, and is extracted from moisture-producing rooms. Boost controls increase extraction when someone showers, cooks or uses a utility space.

This is a whole-home solution. When designed well, it provides balanced ventilation throughout the property rather than addressing one room at a time. It is often the natural choice for new builds, major renovations and airtight homes where duct routes can be planned before ceilings and finishes are completed.

Where central systems work best

Central MVHR is particularly well suited to detached houses, larger extensions and new developments. It can also be a strong option for flat schemes where services are coordinated early and each dwelling receives its own system.

Its main advantage is control. A competent design can account for room use, occupancy, duct lengths, noise control, access for filters and the airflow rates required by the project. It can deliver consistent ventilation across several bedrooms and wet rooms from one carefully commissioned system.

The trade-off is installation complexity. Ductwork needs space, careful routing and proper insulation where required. Retrofitting it into a finished home may involve opening ceilings, boxing in services or working around structural constraints. Poor duct design, sharp bends or undersized ductwork can create noise and reduce performance, so this is not a system to treat as a simple appliance installation.

What are decentralised heat recovery units?

Decentralised units, also called single-room heat recovery ventilation units, are installed through an external wall. Each unit serves an individual room or a defined area. They extract stale air and bring in fresh air through the same wall-mounted device, recovering heat as the air passes through the unit.

Some decentralised systems operate in matched pairs. One unit extracts while the other supplies, then they reverse direction in sequence. Others have separate supply and extract paths within one unit. The arrangement matters because the building still needs a clear, controlled airflow strategy, not a collection of isolated fans fitted wherever condensation is most visible.

For an existing home, the appeal is obvious. Installation generally requires core drilling through an outside wall rather than running ductwork through the whole property. A bedroom, living room, home office or problematic bathroom can be upgraded with far less disruption than a full central system.

Where decentralised units work best

Decentralised ventilation is often the practical choice for occupied homes, flats and targeted mould or condensation problems. It is especially useful where there is no realistic route for extensive ducting, or where a homeowner wants to improve air quality room by room.

It can also suit phased upgrades. For example, a landlord may start with the bedrooms most affected by mould, then add units as refurbishment work takes place elsewhere. This can spread costs and reduce disruption, provided the overall ventilation plan remains appropriate for the property.

The limitation is that each unit has a local role. A larger house may need multiple units to achieve balanced coverage, and positioning must be considered carefully. A unit placed close to a bed, sofa or desk needs suitable acoustic performance and correctly selected operating speeds. External wall access, façade appearance and available power supplies also need checking before work begins.

Central MVHR vs decentralised units: the key differences

The most useful comparison is not centralised versus decentralised in isolation. It is whole-property performance versus targeted, low-disruption installation.

A central system has a higher upfront installation burden because of the unit, ductwork, terminals, controls and labour involved. In a new build, however, this work can be integrated into the programme, making it a sensible long-term investment. In a finished property, the same system may become costly if access is limited or decorative finishes must be disturbed.

Decentralised units usually have a lower barrier to entry. They avoid most internal ductwork and can be installed in selected rooms. Yet fitting several high-quality units across a larger home can narrow the cost gap. The cheapest route is not always the best value if the result leaves bathrooms, bedrooms or circulation areas without the airflow they need.

Central systems tend to offer a more discreet visual result indoors, with ceiling or wall terminals rather than room-mounted units. Their main fan is also located away from occupied rooms, although air movement through ducts can still create noise if the design is poor. Decentralised units are visible within the room, and their sound level is more immediately noticeable, particularly at night. Product selection, installation quality and commissioning matter greatly in both cases.

Maintenance is different rather than difficult. A central MVHR unit normally has filters to inspect and replace, along with terminals and condensate arrangements that need periodic attention. Decentralised units have individual filters and, depending on the model, heat exchanger cores that require cleaning. With several units, maintenance is repeated room by room. A system that is easy for the occupier to reach and understand is more likely to keep working as intended.

Do not overlook ventilation design and compliance

Ventilation is not solved by choosing a product from a specification sheet. Airflow rates, room use, building fabric, background infiltration, cooker extraction and transfer routes all affect the outcome. A powerful bathroom fan or heat recovery unit cannot compensate for a home that has no path for replacement air to move through it.

For new homes, material alterations and many renovation projects, ventilation should be considered against the relevant Irish Building Regulations and Technical Guidance Document F, including the requirements that apply to the scope of work. Builders, developers and property managers should also plan for testing, balancing and documentation rather than leaving ventilation until final snagging.

Commissioning is where a design becomes a working system. It verifies actual airflows, allows adjustments to be made and provides evidence that the installation performs as intended. This is vital for central MVHR, where every branch of ductwork affects the balance, but it is also valuable for decentralised installations where unit settings and room coverage must be checked.

Choosing the right route for your property

Start with the building, not the brochure. A new, airtight family home with several bedrooms and bathrooms will often benefit from a central MVHR design planned alongside the other services. A lived-in semi-detached house with repeated condensation in two bedrooms may be better served by decentralised heat recovery units, perhaps alongside improved extraction in wet rooms.

For flats, external wall availability and management-company requirements can influence the decision as much as technical preference. In commercial settings, occupancy patterns, internal layouts and the need for documented performance often make a designed central solution more appropriate, although localised units can be useful in small offices, treatment rooms or refurbished spaces.

A site assessment should look beyond the visible mould. It should identify moisture sources, check existing extract ventilation, consider the condition of windows and insulation, and establish whether there is enough practical space for ducting. At PureAir Solution, that means matching supply, installation and commissioning to the property rather than forcing every project into one system type.

The best ventilation system is the one residents can live with every day: quiet enough for sleep, accessible enough to maintain, capable of controlling humidity, and verified to deliver the airflow the building needs. Begin with a proper survey, then choose the solution that protects both the fabric of the property and the health of the people inside it.