Decentralised Ventilation in Berlin
Single-room solutions without complex ductwork.
Decentralised ventilation units are the fast, affordable solution for individual rooms without an extensive duct network. Each unit requires only a small core-drilled hole in the outer wall. Ideal for Berlin old-build properties where central systems are architecturally difficult to realise.
Retrofitting decentralised ventilation in a Berlin period building: core drilling, landlord and owners' association
Decentralised ventilation needs no duct network, no suspended ceiling and no plant room. Each unit needs one core hole through the external wall; behind it sits the fan with its ceramic heat store, inside a cover, outside a weather grille. That is exactly why it is the solution that can be retrofitted in an occupied Berlin apartment in a single day. Solid brick walls of 50 to 70 centimetres are no obstacle, they only extend the drilling time; in prefab concrete buildings we check the position of the reinforcement first. On facades with stucco or under heritage protection we place the hole on the courtyard side or in a window reveal so the street elevation stays untouched.
One question must be settled before drilling: who owns the wall? In a rented flat you need the landlord's written consent, in a condominium a resolution of the owners' association, because the external wall is common property. We supply the unit's data sheet, its sound values and a sketch of the drilling positions, just as we have done for air conditioning units for years. In conservation and heritage areas we agree the position with the district office in advance. In our experience this coordination takes longer than the installation itself, so we start it in parallel with choosing the units.
Decentralised ventilation with heat recovery: what a pair of units costs and what the price includes
Decentralised units work in alternating pairs: for around 70 seconds one unit pushes stale air out and charges its ceramic store with heat, then the direction reverses and the incoming fresh air picks that heat up again. This keeps 70 to 85 percent of the heat in the room. One pair typically serves two rooms, for example bedroom and living room. Our price for a pair includes both core holes, the units with inner cover and outer grille, the electrical connection to an existing circuit, the controller and commissioning with a briefing.
Shown separately are surcharges that only affect some apartments: a new cable if no circuit is nearby, scaffolding or an aerial platform if the outside of the hole cannot be reached from a balcony or window, and restoring stucco or render on the facade. Ask for these items in every comparison quote, because a unit price without drilling and connection is only half the bill. The price becomes binding after measuring on site; all figures on this page are guide values from our Berlin projects.
Mould and damp in the apartment: when opening windows is no longer enough
The most common reason for decentralised ventilation is not the energy price but a damp corner in the bedroom. After new windows or an insulated facade the apartment is so airtight that the moisture from cooking, showering and breathing no longer escapes on its own. Nobody in a working household manages to air the rooms three or four times a day. A pair of units with a humidity sensor then exchanges the air exactly when humidity rises above 60 percent and otherwise runs on its quiet base setting.
The order matters: existing mould must be remediated first, the cause at the thermal bridge must be known, and then ventilation prevents a relapse. If the external wall is uninsulated and the damage sits on a thermal bridge, ventilation alone is not enough and internal or facade insulation is needed as well. We tell you at the site visit which case applies to you, because we offer both from one source and have no interest in selling a unit that does not solve the problem.
Decentralised or central residential ventilation: which solution suits your apartment
A central residential ventilation system with ducts achieves 85 to 95 percent heat recovery, serves all rooms from one unit and is practically inaudible in operation. For that it needs ducts in every room, so either a full refurbishment, a suspended ceiling or usable shafts. In an occupied period apartment that is rarely feasible. The decentralised variant gives up the last ten percent of efficiency and gains retrofittability: no duct, no ceiling, one day of installation per pair of rooms.
Our rule of thumb: if the apartment is being gutted anyway or it is a detached house with attic and basement, the central system pays off. If the apartment stays occupied, it is about two to four rooms or consent for larger works is missing, decentralised ventilation is the right choice. The federal government funds both routes equally: a 15 percent grant on the system technology, 20 percent with an individual renovation roadmap. Our dena-listed energy consultant submits the application before the order is placed, otherwise the grant is lost.
Retrofitting decentralised ventilation: costs in Berlin
Guide values from our Berlin projects, each including core drilling, unit, connection to an existing circuit and commissioning. Where your project lands in the range depends on wall construction, accessibility of the outside, unit features and the number of rooms.
| Service | Typical price range | Duration |
|---|---|---|
| Standard pair with heat recovery, two rooms in alternating operation | 2,000 to 3,125 euros | 1 day |
| Premium pair with humidity sensor, pollen filter and app control | 3,000 to 4,500 euros | 1 day |
| Three-room apartment with four units | 4,000 to 6,250 euros | 1 to 2 days |
| Surcharge per core hole in solid brick or reinforced concrete | 150 to 300 euros | after survey |
| Surcharge scaffolding or aerial platform for inaccessible facade | 300 to 900 euros | after survey |
| Filter change and maintenance per year | 60 to 120 euros | annually |
All figures are guide values, not fixed prices. The quote becomes binding after measuring on site. The 15 or 20 percent grant is not deducted here and requires the application to be filed before the order is placed.
Our services in detail
Why Montali?
We combine academic analysis with master craftsman excellence. This means: well-thought-out planning, efficient execution and communication you might not expect from a trade company. As a Berlin master craftsman company, we take responsibility – from subsidy consulting to final sign-off.
Frequently asked questions about Decentralised Ventilation in Berlin
Central KWL supplies all rooms via a shared duct network and typically achieves 85–95 % heat recovery. Decentralised units work room by room with small individual devices (~90 cm × 25 cm × 25 cm) and achieve 70–85 % recovery via ceramic heat exchangers. Decentralised systems are significantly cheaper (€1,000–1,500/unit vs. €6,250–15,000 for central KWL), easier to retrofit, and have no ventilation hoses in the house. Disadvantage: lower efficiency and higher power consumption with multiple units. Particularly in Berlin old-builds, often the best compromise solution.
Decentralised units produce 25–35 dB(A) at normal operation (level 2–3 of 4) – about like quiet conversation. On level 1 they drop to 20–25 dB(A), on highest level 40–45 dB(A). The outdoor unit produces typically 40–48 dB(A) from 2 m distance. With acoustic accessories (elastic mounts, sound-damped pipes) the level can be reduced by 3–5 dB. The best solution is correct manufacturer selection and installation – some units are noticeably quieter than others.
A core-drilled hole (Ø 75–100 mm) in the outer wall requires written landlord consent and possibly homeowners' association (WEG) approval for multi-unit properties. Usually unproblematic since the installation is reversible (hole gets sealed after moving). We prepare a consent letter for the landlord and coordinate with any scaffolding or facade work. With listed building protection, planning permission from the monuments authority is required – complicates installation but is feasible.
As a rule of thumb: 1 decentralised ventilation unit per 40–60 m² living space, minimum 1 unit each for bedroom and kitchen. An 80 m² apartment typically needs 2–3 units in alternating operation (1 supply-air unit bedroom, 1 extract-air unit kitchen, possibly 1 more unit for living room). This gives total costs of €3,750–6,250 for complete coverage. Central KWL would be similarly priced but significantly more efficient. We advise based on layout and usage.
For single-family homes no permit is required. For multi-unit properties you need landlord consent (usually unproblematic) and WEG approval in larger complexes which we verify upfront. For listed buildings an authority permit is required – this can take 4–8 weeks but is usually granted. Costs for permit: €250–625. We apply for this and often can offer an alternative (e.g. surface-routed piping) if core-drilling is denied.
Theoretically yes, practically difficult – decentralised ventilation units have wall penetrations and cannot simply be 'plugged in' to central systems. If your old-build is later renovated and you want central KWL, the decentralised units must be removed and new ducts routed. Costs for this conversion about €3,750–7,500. But that's a thought for 15–20 years down the line. Today decentralised is the quickest and most cost-effective solution – you can always upgrade later.
Yes. Ventilation systems with heat recovery count as system technology in the federal funding for efficient buildings and receive a 15 percent grant, 20 percent with an individual renovation roadmap. Requirements are units with sufficient heat recovery, application before placing the order and confirmation by a listed energy efficiency expert. We handle that step because our energy consultant is dena-listed. Alternatively, 20 percent of the costs can be deducted from income tax over three years; both together is not possible.
Against mould caused by overly humid room air, yes. Two people release around one litre of water into the air overnight, and with the window closed the humidity in an airtight period apartment quickly rises above 70 percent. A unit with a humidity sensor removes this moisture continuously. If the mould sits on a cold thermal bridge, for example the outer corner behind the wardrobe, the wall must additionally be insulated. Existing mould is remediated before installation, otherwise the ventilation spreads the spores.
Yes. The ceramic store transfers the heat of the exhaust air to the incoming fresh air, so even at sub-zero temperatures the air enters the room pre-warmed and there is no draught. At very low temperatures condensate can freeze inside the unit; modern units detect this and briefly run in exhaust direction only until the store is clear again. Decentralised ventilation does not need a frost protection heater. All that matters is keeping the outer grilles free of leaves in autumn.
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