Requirements for ventilation concepts in residential buildings

The comfort of living spaces depends to a large extent on the quality of the air. For example, air with a high CO² content can cause fatigue and headaches, while air enriched with pollutants can even lead to long-term damage to health. Accordingly, it is important to develop an individual ventilation concept that suits the rooms and their users. This article explains which aspects need to be taken into account.


Why do you need a ventilation system at all?

There are many reasons for permanent air circulation in buildings. These include, above all, unpleasant odours, high humidity as well as fine dust and viruses. These air pollutants are problematic insofar as modern buildings are built particularly tightly in order to reduce energy losses as much as possible. As a result, there is practically no free ventilation through gaps and cracks. This makes an additional exchange of air through open windows necessary.

However, if this can only be done in the morning and evening, the supply of fresh air is often insufficient. In addition, open windows lead to heat loss and thus to higher costs. For these reasons, a ventilation system is often required in new buildings and renovated existing buildings. It ensures sufficient air exchange even without opening windows and, depending on the model, offers additional heat recovery. In order to take full advantage of these benefits, however, a few things need to be taken into account during the planning stage.


Requirements for ventilation systems

A detailed ventilation concept provides information about which form of ventilation is best suited for the respective area of application. Depending on the circumstances, the DIN 1946-6 standard (ventilation of dwellings) distinguishes between four levels, each with its own requirements for air quality.

1. Ventilation to protect against moisture

This form of basic ventilation ensures that moisture damage does not spread during absences and vacancies.

2. Reduced ventilation

Reduced ventilation removes pollutants from the air and ensures building protection even during medium-term absence.

3. Nominal ventilation

This form of ventilation is the standard type. It ensures a minimum hygienic standard and protection against structural damage.

4. Intensive ventilation

Ventilation of this type is required when the air has high humidity values at times. This is typically the case in kitchens and bathrooms.


The right ventilation for every application

Depending on the type of building, ventilation requirements and individual wishes, different types of ventilation systems are used. The most important are the following.

1. Exhaust air systems

Systems in this category are comparatively simple in design and are similar to those installed in interior bathrooms. A fan draws in the moist air from the kitchen and bathroom and transports it outside via exhaust air pipes. This creates a negative pressure that draws in fresh air from other rooms through door slots and other openings, which in turn are supplied through external diffusers in the house wall. Effective protection against contamination is ensured by replaceable filters. A disadvantage of the technology is that only comparatively small amounts of air are transported.

2. Central supply and exhaust air systems

In this category, the air flows through a central supply and exhaust duct, so that no diffusers in the house wall are required. Humid air from the bathroom and kitchen is drawn in and transported outside via exhaust ducts. Fresh air is sucked in from the outside area and fed into the living rooms via supply air ducts.

In the interest of optimal functioning, the following factors must be taken into account during planning:

  • the room air requirement
  • the size of the flat
  • the size of the household
  • Cleaning possibilities

3. Decentralised supply and exhaust air systems

Decentralised supply and extract air systems are characterised by the fact that they are very compact and do not require any additional ducts.

The diffusers are installed in the house wall. This has several advantages. On the one hand, new and existing buildings can easily be equipped with them, and on the other hand, the technology is cheaper than with a central supply and exhaust air system.


Different types of heat recovery

Ventilation systems equipped with heat recovery, as we also offer at LUNOS, open up great energy-saving potential. They extract heat from the exhaust air, which can then be used to heat rooms and water. In this way, the efficiency of the ventilation system can be significantly increased and the energy demand of the building reduced.

Depending on which technology is used, a distinction is made between different types of heat recovery systems.

Air-to-air heat exchanger:

With this technology, the warm extract air duct is led past the cold supply air duct, whereby the heat is transferred to the incoming air. If it is a decentralised supply and extract air system, the air exchange takes place within a single unit in the external wall.

Heat pump:

This alternative to the heat exchanger extracts its heat from the exhausted air and feeds it into the heating system. It can also be used to heat domestic hot water.

Ground heat exchanger as an add-on, e.g. on central ventilation systems:

Supply air pipes can also be installed in the ground. Especially in summer, this has the advantage that the supply air is led into the house at the lower temperature of the ground. However, it is important to lay the air ducts at a gradient, as otherwise the condensation moisture that accumulates can lead to bacterial and mould infestation. But even beyond this, there is always the risk of microbial contamination, which is why the technology is not recommended by the Federal Environment Agency.

Ground-source heat exchangers as an add-on, e.g. to central ventilation systems:

If the property is large enough, ground-brine heat exchangers are also a possibility. In this case, the geothermal heat is first transferred to a downstream brine-air heat exchanger, which largely eliminates any adverse effect on the supply air.

What to consider when planning ventilation systems

If you are planning a new building or a renovation, you should think about the design of the ventilation system as early as possible. The following factors in particular play a role here.

Air tightness of the building envelope:

To ensure that the ventilation system functions effectively, the building must be sufficiently airtight. This can be determined with the blower door test. This ensures that supply air enters the rooms exclusively through the intended ventilation openings and not uncontrolled through gaps and joints.

Positioning of the exhaust air zones:

The rooms from which extract air is extracted should be as close together as possible. This avoids risers and long horizontal ducts, which in turn reduces costs and materials.


Energy consumption is caused by the fans installed in the system. If the system is for a flat, the lowest level is usually sufficient. For single-family houses, you have to allow for an annual consumption of 200 - 400 kilowatt hours. If you use a well adjusted ventilation system, you can save considerably more energy than you consume.


A ventilation system must be permanently in a clean condition so that it can work efficiently. The prerequisite for this is that sufficient openings are planned for maintenance and that the supply and exhaust air ducts are protected as best as possible against dust and contamination, even during the construction phase.

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