Planning KWL: Controlled ventilation with heat recovery
A modern controlled domestic ventilation system (CDVS) with heat recovery saves up to 50% on heating costs, ensures hygienic indoor air, and is affordable with subsidies. The background: The more densely insulated and sealed buildings become, the less natural air exchange occurs—moisture, CO₂, and odors remain in the house, and manual window ventilation is hardly sufficient to reliably compensate for this.
A CDVS systematically solves this problem: it continuously exchanges air as needed, without valuable heating warmth being lost through open windows. This guide will take you through the planning—from how it works, to device selection, to subsidies—and shows what matters for a system that is expected to run reliably for two decades.
What is CDVS and how does heat recovery work?
The basic principle is simple: fresh outdoor air comes in, stale air goes out—the heat exchanger transfers the heat from the exhaust air to the supply air. The two airflows cross paths without mixing: they flow through separate channels of the exchanger, only the heat travels through the thin dividing walls from the warm exhaust air to the cold fresh air. This allows for up to 95% heat recovery—the supply air enters the rooms already pre-warmed, even if it's winter outside.
In practice, the supply air is directed into living areas like living rooms and bedrooms, while the exhaust air is extracted from wet rooms—kitchen, bathroom, toilet. The air thus flows through the apartment specifically from the clean to the contaminated areas. Key figures:
- 70–95% heat recovery
- 50% heating cost savings
- 20–25 years lifespan
Heat recovery distinguishes between two concepts: passive HRU exclusively transfers existing heat via the exchanger, while active HRU combines the exchanger with an integrated heat pump that additionally extracts heat from the exhaust air—allowing the device to also prepare hot water or actively heat.
Passive HRU
- Counter-flow heat exchanger
- Efficiency 70–90%
- Devices: Nilan Comfort 200/300
- Cheaper to purchase
Active HRU
- With integrated heat pump
- Effective efficiency > 100% (COP 3–5)
- Devices: Nilan Compact P, Combi
- BEG funding possible
Whether a central or decentralized system is better suited for your building is clarified in the comparison Central vs. Decentralized Ventilation.
Which CDVS device for which living space?
The size of the device depends on the required volume flow—i.e., the amount of air that needs to be exchanged per hour. This is determined by living space, room height, and number of occupants. An undersized device will constantly run at its performance limit, become loud, and wear out faster; a significantly oversized one costs unnecessary money and excessively dries out the indoor air in winter.
The correct dimensioning is therefore somewhere in between: the device should comfortably manage nominal operation in the middle speed range and still have reserves for peak loads—such as cooking or many guests. The following overview assigns the Nilan devices to typical living spaces.
| Living Space | Recommended Device | Volume Flow |
|---|---|---|
| ≤ 120 m² | Nilan Comfort 200 | 200 m³/h |
| 120–200 m² | Nilan Compact P | 300 m³/h |
| 200–300 m² | Nilan Combi 302/400 | 400 m³/h |
| Multi-family house | Nilan VPM 1200/1500 | 1200–1500 m³/h |
Complete devices can be found in the category Ventilation Systems, models with integrated heat pumps under Heat Pumps.
Advantages and Disadvantages of CDVS
A CDVS is a long-term investment, and it needs to be carefully considered. On the plus side, in addition to energy savings, the main advantages are living quality: constantly fresh air without drafts, filtered supply air without pollen and road dust, and effective protection against mold, because moisture peaks from bathrooms and kitchens are continuously removed. Allergy sufferers and residents on busy roads particularly benefit noticeably.
This is offset by the investment costs and moderate ongoing expenses. Filter replacement is not a trivial matter, but a prerequisite for hygienic operation—anyone who shies away from it should reconsider the decision for a CDVS. In old buildings, ducting is an additional planning challenge, as routes for pipes must be found through ceilings and walls retroactively.
Advantages
- Up to 50% heating cost savings
- Better air quality (F7/F9 filters)
- Mold protection through exhaust air
- Allergy-friendly
- Constant CO₂ values
- No shock ventilation needed
Disadvantages
- Investment 5,000–15,000 € (funding possible)
- Filter change every 6–12 months
- Power consumption 50–200 kWh/year
- Possibly needs sound attenuators in bedrooms
- Extensive ducting in old buildings
Maintenance and Funding
A CDVS is low-maintenance, but not maintenance-free. The majority of the care is routine that you can do yourself: changing filters and occasionally cleaning the valves. Only work on the internal components—heat exchanger, fan, duct system—should be handled by a specialist, and this is only required at long intervals.
By adhering to these intervals, you not only ensure hygiene but also economic efficiency: soiled filters increase resistance, drive up power consumption, and reduce heat recovery. You largely recover the maintenance costs through the maintained efficiency.
Maintenance Intervals
| Component | Interval |
|---|---|
| Outdoor air filter (F7) | 6 months |
| Exhaust air filter (M5) | 3–6 months |
| Clean heat exchanger | annually |
| Ventilation system service | every 2 years |
| Duct cleaning | every 5–8 years |
Pro tip: You can change the filter yourself in 5 minutes; a specialist should handle the heat exchanger and service. The Maintenance Plan for Ventilation Systems shows all intervals in detail.
Funding
Regarding investment costs, it is worth looking into government subsidies, as they can significantly change the calculation. A CDVS with an active heat pump is eligible for up to 70% funding through the BEG program—you can read the details in the article on Heat Pump Funding 2026. Pure ventilation units are funded through KfW Efficiency House programs. Important in both cases: the funding application must be submitted before commissioning—so plan the application phase into the project timeline from the start.
Frequently Asked Questions
Do I still need heating with CDVS?
With active HRU (Compact, Combi) and a well-insulated house, CDVS can suffice for heating. With passive HRU, a separate heating system remains necessary—CDVS then reduces its consumption.
How loud is a CDVS?
In living areas, 25–35 dB(A). With sound attenuators, barely audible. Planning is crucial: device location, decoupled mounting, and sound attenuators before bedrooms.
Is CDVS possible in old buildings?
Yes, but renovation is extensive. It's worthwhile with comprehensive modernization—then duct routes can be planned together with other trades.
What does a CDVS cost?
Single-family home ~150 m²: 5,000–10,000 € for devices plus 5,000–10,000 € for installation. With funding, effective additional costs approx. 50%.
Conclusion
A well-planned CDVS reduces heating costs, protects against mold, and consistently provides fresh air—and with a lifespan of 20–25 years, it's an investment that pays off over its entire period of use. Three things are crucial for success: the right device size for your living space, precise planning of ducting and sound insulation, and consistent maintenance during operation. Anyone who also utilizes funding opportunities before commissioning will significantly reduce the effective costs. Everything for your comfort ventilation—from the device to the filter—can be found in the ventilation range at wohnungstechnik.de.
