Updated on 24.8.2026
Smart ventilation protects your most important investment – your home. Modernisation of ventilation is an important part of a renovation project. Almost half of the heating energy consumption in a traditional house is caused by ventilation. This is why the energy-efficiency of a ventilation system plays a major role in the efforts to save energy.
Heating system renovation, additional insulation and window replacement improve the airtightness of the building and reduce air leaks. Therefore, it is particularly important to modernise the ventilation system so that it supports the energy saving goals of the renovation project. The savings must not be achieved at the cost of the quality of indoor air or the health of the structures. Inadequate ventilation causes moisture damage to the structures and makes them susceptible to mould growth.
When Should a Ventilation System Be Replaced?
Especially in detached houses built before the 1980s, ventilation is often based on a natural ventilation system, where air exchange occurs naturally through the effects of temperature differences and wind via ventilation openings and relatively leaky building structures.
Converting a ventilation system to mechanical ventilation is advisable when extensive renovations are carried out to improve the airtightness of the building, for example by adding insulation and replacing windows and doors. In such cases, natural ventilation no longer functions adequately because uncontrolled air leakage is significantly reduced. In an airtight building, a controlled mechanical ventilation system is essential to ensure sufficient and healthy indoor air quality.
Insufficient ventilation following renovation work can also lead to excessive moisture accumulation within building structures, potentially resulting in mold damage. In addition, a ventilation system equipped with heat recovery supports the energy-efficiency goals of the renovation by reducing heat losses and improving overall building performance.
Effective Ventilation Protects Against Moisture
If indoor humidity levels become too high, moisture can easily condense on window surfaces or within cold external wall structures. Prolonged exposure to moisture creates conditions that promote microbial growth and the development of mold, which can eventually cause significant damage to building structures.
An efficient mechanical ventilation system, such as a MyVallox ventilation unit, removes carbon dioxide, excess moisture, odours, and airborne pollutants from the building in a controlled manner. In addition, heat recovery based on a plate heat exchanger prevents contaminants in the extract air from mixing with the incoming fresh air, further improving indoor air quality.
Mechanical Ventilation Design and Sizing
When converting a building to a mechanical ventilation system, several key factors must be considered during the design and implementation phases. These include the correct sizing of the ductwork and the feasibility of installing the duct system within the existing building structures. In addition, the ventilation unit must have sufficient capacity to provide the required airflow rates for the building, ensuring that the system operates efficiently and as intended.
Finally, the airflow rates must be carefully balanced to achieve a comfortable and healthy indoor environment. The design and implementation of these elements require the expertise of HVAC professionals. Proper system sizing is essential to ensure that the ventilation unit can deliver the required airflow while maintaining energy-efficient operation.
Is Upgrading to Mechanical Ventilation Worth It?
In many cases, upgrading to a mechanical ventilation system can be considered a worthwhile investment. This is especially true in older houses where ventilation is based on a natural ventilation system and renovation work is often needed. In such properties, once air-tightening measures have been carried out as part of a renovation project, a mechanical supply and extract ventilation system with heat recovery can significantly improve indoor air quality, reduce moisture accumulation, and help prevent mold growth and unpleasant odours.
In addition, heat recovery technology enables energy savings by capturing heat from the extract air and using it to warm the incoming fresh air. This improves the overall energy efficiency of the building and reduces heating costs.
Although installing a mechanical ventilation system can be relatively expensive and may require structural modifications, the long-term benefits, such as improved living comfort, healthier indoor air, and potential increases in property value, often make the investment worthwhile.
However, the decision to upgrade to mechanical ventilation should always be made on a case-by-case basis, taking into account the characteristics of the building as well as the needs and expectations of its occupants.
Examples of Ventilation Renovations in Detached Houses
Ventilation renovation of a one-and-a-half-storey house built in the 1950s
The one-and-a-half-storey house built in the 1950s was renovated to meet today’s living requirements. The windows, entrance doors, kitchen and sauna facilities were renovated, and the cellar was replaced with a combined fireplace room and exercise room. Because the renovation considerably increased the airtightness of the building, natural ventilation was replaced with a mechanical supply and extract system.
Transverse ventilation ducts were placed almost completely within the cellar. The living areas required only vertical ducts and a few short horizontal ducts that were easily made invisible with the help of enclosures. Exhaust air was led out through the cellar wall.
The ventilation unit chosen was Vallox 110 MV, mounted near the sauna facilities in the cellar. The unit is equipped with a built-in humidity sensor, which enables automatic ventilation boosting after bathing.
Ventilation renovation of a one-family house with a low-height attic
Natural ventilation was replaced with modern low-energy ventilation. The low attic space did not allow the ventilation ducts to be installed in the traditional way.
The Vallox BlueSky air distribution system, which is based on a small and flexible ventilation duct, was mainly mounted on the walls in the entrance hall. The ducts were encased, and additional lighting was installed on the bottom surface of the cases. Installing the ducts indoors also eliminated the need for insulating the ducts from the cold.
The ventilation unit chosen was Vallox 110 MV, installed in the changing room close to the sauna facilities. The unit is equipped with the easy-to-use MyVallox Control control system that is based on the choice of mode and enables an automatic ventilation efficiency adjustment according to the humidity content of air.
