Ventilation system

Ventilation system - a technical system for the controlled ventilation of living spaces that exhausts stale air to the outside while simultaneously supplying fresh outdoor air, without the need to open windows. In the real estate industry, controlled residential ventilation (CRV) plays a central role, particularly in energy-efficient retrofitted buildings and new construction.

Centralized and Decentralized Systems Compared

In a centralized ventilation system, a single unit-usually installed in the basement, attic, or utility room-supplies all rooms in the apartment or house via a duct network. Air is introduced into living rooms and bedrooms through supply air vents and extracted from the kitchen, bathroom, and toilet through exhaust air vents. Centralized systems achieve high heat recovery rates of 80 to 95 percent and operate particularly efficiently in new buildings, where the ventilation ducts are planned during the construction phase.

Decentralized ventilation units, on the other hand, are installed directly into the exterior walls of individual rooms. They are ideal for retrofitting existing buildings, as no ductwork needs to be installed. The units operate in pairs on a rotating basis: while one exhausts air to the outside and stores heat in a ceramic core, the other brings in fresh outside air and releases the stored heat. Heat recovery in decentralized systems ranges from 70 to 90 percent.

DIN 1946-6 specifies when a ventilation plan must be developed. For new buildings and energy-efficient renovations-such as when replacing more than one-third of the windows or installing roof insulation-proof of sufficient minimum air exchange is mandatory. Often, this can only be ensured with a mechanical ventilation system, as the airtight building envelope no longer allows for natural air exchange.

Heat Recovery and Energy Savings

A key quality feature of modern ventilation systems is the heat recovery efficiency. This indicates how much of the heat contained in the exhaust air is used to heat the fresh air. In high-quality central systems, 85 to 95 percent of the heat is recovered-which means that even when the outside temperature is minus 10 degrees, the incoming fresh air is preheated to over 18 degrees without the heating system having to kick in.

Over the course of a year, a ventilation system with heat recovery can reduce a building’s heating requirements by 20 to 40 percent. This directly impacts heating costs and is often essential for meeting energy-efficient building standards (e.g., KfW 55 or KfW 40). Anyone wishing to take advantage of federal subsidies for energy-efficient buildings (BEG) will find it nearly impossible to avoid installing a mechanical ventilation system in highly insulated buildings.

Mold Prevention, Maintenance, and Costs

A key argument in favor of a ventilation system is protection against mold growth. In well-insulated buildings with airtight windows, manual ventilation is often insufficient to reliably remove humidity-especially in bedrooms and bathrooms. The ventilation system ensures continuous air exchange and maintains relative humidity within the recommended range of 40 to 60 percent.

Costs vary significantly depending on the system and building size. Decentralized single-room ventilators cost between 300 and 800 euros per unit plus installation-for an apartment, we estimate 3,000 to 6,000 euros. Centralized systems with heat recovery, including ductwork and installation, range from 8,000 to 15,000 euros for a single-family home.

Regular maintenance is crucial for proper function and hygiene. Filters should be replaced every three to six months; we recommend professional maintenance with duct cleaning every two to three years. Dirty filters increase electricity consumption and can degrade air quality.

Practical Tip for Nuremberg and Franconia

In the Nuremberg metropolitan region, the topic of ventilation systems primarily concerns the numerous post-war buildings from the 1950s to the 1970s, which are currently undergoing energy-efficiency renovations. Anyone planning a complete renovation with new windows and facade insulation in Südstadt, Langwasser, or Fürth cannot do without a ventilation concept compliant with DIN 1946-6.

For retrofitting in existing apartments, we recommend decentralized units, as they do not require complex ductwork and can also be installed in rented condominiums. Especially in Nuremberg’s Wilhelminian-style buildings with solid brick walls, the core drilling required for decentralized units is technically straightforward and can be completed quickly. Grants from KfW (Federal Funding for Efficient Buildings) or the Bavarian Modernization Program can significantly reduce investment costs-we are happy to advise you on current funding opportunities and, upon request, coordinate the entire process.

Frequently Asked Questions About Ventilation Systems

Does a ventilation system make sense in an older building?

Yes, especially after an energy-efficient renovation. Once new windows and exterior insulation seal the building envelope, the natural air exchange through gaps and cracks is lost. A decentralized ventilation system with heat recovery prevents mold, saves heating energy, and ensures a healthy indoor climate-without the need for constant manual ventilation.

How loud is a ventilation system?

Modern ventilation units operate at the lowest setting with a sound level of 15 to 25 decibels-comparable to the ticking of a clock. Decentralized units in bedrooms should be specifically set to night mode so as not to interfere with sleep comfort. We recommend paying attention to the measured sound power level when selecting a product.

What filters are needed, and how often do they need to be replaced?

Standard ventilation systems use coarse dust filters (G4/ISO Coarse) and fine dust filters (F7/ISO ePM1). The coarse filter protects the unit, while the fine filter traps pollen and fine dust. Filters need to be replaced every three to six months-more frequently during high-pollen seasons if necessary. Filter costs range from 20 to 50 euros per replacement.

Does a ventilation system need to be explained to the tenant when renting?

Yes. As a landlord, you are obligated to instruct the tenant on the operation and maintenance of the ventilation system. Incorrect operation-such as leaving the system turned off permanently or neglecting to change the filter-can lead to mold, which can then give rise to disputes over liability. We recommend providing written instructions and a maintenance schedule as an attachment to the lease agreement.

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