Ventilation systems: how to get fresh air with comfort

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Controlled residential ventilation, or KWL for short, is difficult to do without in modern types of building. Read at effizienzhaus-online, between which types you can decide, where the advantages and disadvantages lie and how much a ventilation system costs on average!

Automatic air exchange for well-insulated buildings

Controlled living space ventilation serves to improve the living climate. It regulates humidity and thus prevents the formation of mold. Regular air exchange is mandatory in well insulated buildings with airtight envelope, because it does not occur by itself through joints and gaps.

The simplest solution is regular airing. But this is neither particularly convenient nor very reliable. It is too easy to neglect the air exchange over a longer period of time. Or, on the contrary, the windows remain open. With high heat losses as a result. Energy-efficiently planned buildings and high-quality renovated old buildings combine modern heating and good insulation with automated ventilation.

Ventilation centralized or decentralized?

The most important distinction between ventilation systems is that between centralized and decentralized systems. Decentralized systems supply a single room, while in a centralized residential ventilation system, one system is connected to each room.
The centralized solution is more efficient in itself but also more expensive to purchase. For new buildings, it is therefore usually planned from the outset. In this way, ventilation ducts can be elegantly integrated into the building structure alongside the rest of the building services equipment.
Decentralized solutions are more frequently used in old buildings. They then primarily supply the rooms in which ventilation plays a particularly important role.

Pure exhaust air systems are relatively inexpensive

A further distinction is that between exhaust air systems and aeration and deaeration systems. Pure exhaust air systems occur more frequently than decentralized ventilation systems. You can actively discharge humid air from the bathroom and kitchen. Passively, fresh air can flow into living rooms and bedrooms through vents in doors and windows.
A decentralized exhaust system is straightforward to install with a simple core drilling or a small wall opening. It is the cheapest solution to ensure automatic air exchange for kitchen and wet rooms.

Decentralized ventilation system with heat recovery

More complex and higher-quality forms of decentralized residential ventilation operate as an aeration and deaeration system. In alternating operation the fan switches alternately to exhaust and supply air. Then only one breakthrough is necessary. With two ducts, the system can often operate more efficiently and reliably in comparison.
Usually such systems are combined with a heat exchanger. It can extract up to 75% or more of the heat from the exhaust air and return the energy to the interior with the fresh air. This minimizes the heat loss during ventilation. Passive house standards are virtually unachievable without this feature.

Central, controlled living space ventilation

In a central system, each room is connected to the ventilation system via ventilation pipes this ensures an even, controlled distribution of fresh air throughout the house.
As a rule, only the kitchen and bathroom are connected to the exhaust air system. Moisture and odors can be optimally dissipated. Ducts are in the floor or in a suspended ceiling. The supply air is often drawn from below, while the exhaust air is extracted from above.
In summer, cool air reaches the inside directly via the bypass at night, helping to prevent overheating. The actual, central ventilation system is often located under the roof. With additional sound insulation on the supply and exhaust air pipes, noise pollution can usually be avoided completely.

Advantages and disadvantages of a ventilation system

  • High energy savings when ventilating
  • The air in the living space is always fresh and unused
  • The supply air is pre-cleaned with pollen and fine dust filters
  • Less dust pollution and benefits for allergy sufferers
  • Air can become dry – humidifier prevents it
  • Filters and heat exchangers need to be maintained and cleaned to prevent germination
  • Not or only with difficulty combinable with room air dependent fireplace
  • Flow noise possible at high operating level and unfavorable building conditions
  • In the case of decentralized systems, also fan noise

Plan professionally for good efficiency

The savings effect can be lost with incorrect planning. In continuous operation, no efficiency advantages are then achieved over window ventilation, despite the heat exchanger. A professional planning does not see the living space ventilation as a single measure. Instead, it is optimally adapted to the property as a coherent part of an overall concept that includes all energy-related aspects of the house.

Costs and subsidies of a ventilation system

Those who retrofit a ventilation system in an existing building currently benefit from particularly high subsidies. This is available through the federal funding for efficient buildings (BEG), program 152 of the kreditanstalt fur wiederaufbau (kfw) or the tax office under the following conditions:

– grant or loan with repayment subsidy of 20 to 25 percent via BEG funding (loan as of 01.07.2021)

– tax relief amounting to 20 percent of the renovation costs via the tax bonus for renovations

– tax relief amounting to 20 percent of the craftsmen's wage costs via the tax bonus for craftsmen's services.

It is important that the ventilation system is a central exhaust air system, a central or decentralized ventilation system with heat recovery or a compact unit with an exhaust air heat pump. In addition, retrofitters must apply for the funds with an energy consultant prior to awarding supply and service contracts. Exception: tax bonuses for renovation work and craftsman services can also be applied for retrospectively and without an energy consultant.