frånventilation

Frånventilation is a term sometimes used to describe ventilation that removes air from a building or a room to the outside, typically referred to in Swedish as frånluftventilation. In practice it denotes systems where the majority of indoor air is exhausted and replacement air enters passively or through dedicated make-up air. This type of ventilation is common in older buildings or retrofit projects where a simple exhaust concept is favored over more complex systems.

How it works and typical components

A frånventilation system relies on exhaust fans placed in rooms where air exchange is most needed, such as bathrooms, kitchens or utility spaces. The exhausted air creates a negative pressure that draws outdoor air in through leaks, cracks, vents or dedicated make-up air inlets. In less advanced installations, make-up air is indirect and uncontrolled; in more modern setups, make-up air may be actively supplied to maintain indoor air balance. Ductwork, filters and noise-reducing components are often present, though the system generally lacks a dedicated mechanism to recover energy from the exhausted air.

Advantages and limitations

Advantages include a relatively simple installation, lower upfront cost, and effective removal of moisture, odors and contaminants at their source. Limitations include energy loss from warmed or cooled indoor air, potential negative pressure that can draw in outdoor pollutants or dampness through unwanted openings, and uneven air distribution if the building is not well sealed. The system can also influence indoor humidity and may require make-up air considerations to prevent backdrafting or pressure imbalances.

Applications and context

From-ventilation is frequently used in smaller or retrofit projects and in areas where targeted removal of moisture and odors is prioritized. In modern energy-efficient buildings, balanced ventilation with heat or energy recovery (HRV/ERV) is often preferred to minimize energy waste while providing controlled, whole-house ventilation.