Proper air distribution is critical for comfort, energy efficiency, and healthy indoor air. Unfortunately, this is also one of the most common areas where mistakes are made during installation. Ventilation should be designed so that fresh air mixes evenly with room air, without causing drafts or leaving parts of the room with poor ventilation.
- Key principles of good air distribution:
Diffuser placement: Supply air diffusers should be positioned so that the airflow spreads widely and mixes before it reaches occupants. In living rooms and bedrooms, the air should not blow directly on people sitting or sleeping. - Air velocity: Supply air should enter the room at the right speed — strong enough to spread and mix, but not so strong that it creates a noticeable draft in the occupied zone.
- Temperature difference: Slightly cooler supply air (typically 3–5 °C below room temperature in winter) helps mixing. If supply air is warmer than the room, it may rise and stay at the ceiling, leading to stratification and poor ventilation.
- Balance between rooms: Fresh air must be supplied where people spend time (living rooms, bedrooms) and extracted where pollutants and moisture are generated (kitchen, bathroom, WC). The airflow balance ensures proper circulation through the entire dwelling.
Common mistakes and misunderstandings:
- Diffusers placed too close to people → causes drafts, complaints, and users lowering ventilation unnecessarily.
- Using the wrong diffuser type → for example, simple grilles that blow air straight down instead of swirl or slot diffusers that spread air evenly.
- Too high supply air velocity → leads to noise and drafts.
- Too low supply air velocity → air “falls” before mixing, leaving parts of the room poorly ventilated.
- Placing supply and extract too close together → air short-circuits from supply to extract without mixing into the room.
- Not considering furniture layout → air blowing directly on a bed or sofa leads to discomfort.
- No adjustment after installation → dampers and diffusers should be balanced on site to ensure design airflow rates are achieved.
Why this matters:
If air distribution is wrong, occupants may complain about drafts, poor comfort, or “feeling cold air.” This often leads to users lowering or even turning off ventilation, which then compromises indoor air quality. Good diffuser selection and placement prevent these problems by making the airflow almost unnoticeable — you feel the comfort of fresh air, not the movement of air.
In short: ventilation should be felt as fresh and comfortable, not as moving or cold air. If you can feel the airflow directly, the diffuser type, position, or adjustment is probably not correct and should be reconsidered.