Ventilation Myths #3/8. Demand-controlled ventilation is expensive.
According to modern building practices, it’s no longer possible to build houses with natural ventilation. Buildings are designed to be highly insulated and airtight. Windows have triple seals, and walls do not let air through—whether the house is built from wood, logs, blocks, or concrete. A building constructed to today’s standards requires mechanical ventilation to ensure sufficient air exchange and humidity balance.
A properly designed and executed ventilation system is not costly to operate. If ventilation creates excessive expenses, the reason is usually a poor design or poor implementation.
For room-based demand-controlled ventilation, Aerefy’s projects show a base consumption of only 0.25 W/m², which equals 6 Wh/m² per day. For example, in a 400 m² building that means just 100 W, and with 8 occupants, about 200 W. That’s less than the power used for the building’s lighting—or about half the consumption of a single powerful desktop computer. This translates to 2.2 kWh/m² per year, or roughly 0.9 MWh annually for a 400 m² house. At an average electricity price of €0.10/kWh, the yearly running cost of the ventilation system in this house is just €87.
In A-class energy houses, heating costs during winter are typically 10–30 times higher than ventilation costs. The biggest losses often come from inefficient heat recovery—literally pumping warm air out of the building. So when passive house owners complain about high ventilation costs, the real problem usually lies in energy-hungry systems and poorly executed solutions.
Room-based demand-controlled ventilation also comes with much lower maintenance costs. If there’s no need to keep air moving unnecessarily, filter replacements and duct cleaning are required far less often. Not to mention, the indoor air quality in occupied zones is significantly better.
In well-sealed houses, airflow and ventilation control must also be carefully planned for kitchen hoods and fireplaces, since both require compensation air to work properly. It’s not uncommon to see cases where ventilation pulls cold air back inside through the hood, or where you have to open windows just to light the fireplace for avoiding smoke entering the room.
In low-energy buildings, large part of energy consumption doesn’t come from ventilation or the heating—it comes from the occupants: heating domestic water, running appliances, using computers, and removing excess heat generated by people, household activities, and the sun.
While modern construction has achieved excellent thermal efficiency, managing excess heat removal via ventilation remains a challenge—sometimes even year-round in office buildings even in colder climates.