Both systems bring in filtered fresh air and recover heat from the air they extract. A central system uses one unit and ducts to every room; it usually recovers more heat, filters better and runs quietly from a technical room. Common reversing wall units work in pairs without ducts and suit renovations where ducts will not fit. For a new airtight home, central ventilation is the usual choice, and it is what BioBuilds installs.
An airtight, well-insulated home needs controlled ventilation: opening windows cannot replace stale air fast enough without losing the heat the envelope keeps in. Mechanical ventilation with heat recovery (MVHR) solves both problems. The question for a new home is which layout to choose. This guide compares central and decentral systems on the points that matter for living with them: heat recovery, air quality, noise, maintenance and cost. For what MVHR is and what it costs, see our guide to heat recovery ventilation.
How does central ventilation with heat recovery work?
A central system has one unit, usually in a technical room, utility room or ceiling void. Ducts take fresh air to the living room and bedrooms and extract stale, humid air from the kitchen, bathroom and utility room. In the unit, the two airflows pass each other in a heat exchanger without mixing, so the outgoing air warms the incoming air. Fans run continuously at a low setting and can be boosted for cooking or showers.
Because the whole house runs through one unit, the airflows are balanced, filters can be fine, and the fans sit away from the rooms you live in.
How do decentral ventilation units work?
Decentral units are fans built into the external walls of individual rooms. Most work in pairs: one unit blows air out while the other draws air in, and they swap direction at a fixed interval. A ceramic or similar store in each unit absorbs heat from the outgoing air and returns it to the incoming air on the next cycle. There are no ducts, only wall openings.
Paired reversing units are quick to fit into an existing house, and each device has a fan, filter and wall opening. Other decentral designs supply and extract air simultaneously through a heat exchanger; some can also serve an adjoining room. The number of devices depends on the ventilation design.
Central or decentral: how do they compare?
| Central system | Decentral units | |
|---|---|---|
| Layout | One unit, supply and extract ducts | Wall devices; number and placement depend on the design |
| Heat recovery | Counter-flow heat exchanger; certified units reach high efficiencies | Reversing heat store or continuous-flow heat exchanger; performance depends on equipment and operating conditions |
| Air quality | Fine filters possible at one point; balanced supply and extract | Smaller filters per unit; airflow per room |
| Noise | Unit outside the living rooms; ducts with silencers | Fan in the room's wall, audible in quiet bedrooms |
| Installation | Duct routes planned with the house | Core drill per unit; no ducts |
| Maintenance | Filters changed at one unit | Filters changed at every unit |
| Best for | New builds and full renovations | Renovations where ducts cannot be fitted |
In a new home, ducts can be planned with the house. A central system keeps filter changes at one point and fans out of bedrooms. Compare the certified heat recovery of the actual units: the Zehnder ComfoAir Q450 in the larger BioBuilds homes reaches 88% in its Passive House Institute certificate.
Compare whole-home installed quotes at the same design airflow: include ducts and silencers for a central system, or all wall devices, openings and controls for a decentral system. Include filter replacement and fan electricity costs.
Which ventilation system suits a new low-energy home?
For a new build designed for very low heating demand, a central system is the usual choice. The building envelope keeps heat in; the ventilation system must not lose it again through the air. The Passive House Institute certifies ventilation units only if their effective heat recovery is at least 75% and their electricity use stays low, and central units are designed to reach those figures across a whole home.
Decentral units still have a place: in renovations where there is no space for ducts, or for a single room added to an existing house. In a new airtight home, several pairs of wall units add wall openings, fans in the bedrooms and more filters to change. Compare heat recovery for the chosen equipment at the design airflow.
What ventilation do BioBuilds homes have?
BioBuilds installs central Zehnder ventilation with heat recovery: the compact Zehnder EVO in Wanderlust, and the Zehnder ComfoAir Q450 with the ComfoClime Q module in Serenity, Sanctuary and Bloom. Zehnder rates the ComfoAir Q450 at up to 96% heat recovery; in the Passive House Institute's component certificates, the Q450 reaches 88% and the EVO 84% effective heat recovery, both above the 75% the institute requires. BioBuilds fits Zehnder's standard filter set: ISO ePM1 65% (F7) on the fresh air and ISO Coarse 65% (G4) on the extract air, so the supply filter holds back at least 65% of the finest particles (PM1).
Ventilation is included in the Turnkey finish and is an option in Exterior Finished, where it costs €9,520–€29,155 depending on the model, including an illustrative 19% German VAT. Both finishes are built on BioBuilds' Passivhaus-certified building system. To see the price with your chosen finish, configure your home.
How do you maintain ventilation with heat recovery?
- Filters. Change them on the manufacturer's schedule, and more often near busy roads or fields. Central systems need one set of filters; decentral systems need one per unit.
- Valves and grilles. Clean the supply and extract valves from time to time without changing their settings.
- Settings. Use the boost mode for cooking and showers, and a lower setting when the house is empty.
- Service. A periodic check of the unit, condensate drain and airflows keeps the system efficient.
