Ventilation Adjustment — Balanced and Efficient Ventilation

Correct ventilation adjustment is a prerequisite for good indoor air quality and energy-efficient living. Improperly adjusted ventilation can cause numerous problems: excessive exhaust airflow creates negative pressure in the dwelling, which draws cold air through the building envelope, causing a sensation of draft and, in the worst case, moisture damage.

On the other hand, insufficient ventilation leaves moisture and contaminants in the dwelling, degrading indoor air quality. Properly adjusted ventilation efficiently removes excess moisture and contaminants, provides sufficient fresh air, and maintains balanced pressure in the dwelling without drafts.

Ventilation adjustment is a professional task that requires precise measurements and expertise. The adjustment process proceeds as follows:

• Initial measurement: The airflows of all supply and exhaust air valves are measured with a specialist meter
• Target value determination: The required airflow is calculated for each room based on its intended use
• Valve adjustment: The valves are set to the correct positions to achieve the target airflows
• Unit adjustment: The air handling unit's fan speeds are adjusted according to overall airflow requirements
• Verification measurement: All airflows are re-measured to confirm the final result

The adjustment is documented in a report that records the measured airflows for all valves. This document is useful for future maintenance.

Older buildings often have gravity-based ventilation, where performance relies on temperature differences and wind effects. Gravity-based ventilation is often insufficient, especially in summer and mild autumn, when the temperature difference between indoor and outdoor air is small.

Gravity-based ventilation can be improved in several ways:

• Supply air valve installation: Adequate replacement air supply is a prerequisite for gravity-based ventilation to function
• Exhaust fan installation: A fan installed at the top of the chimney boosts extraction
• Apartment-specific mechanical ventilation: A separate supply-exhaust unit provides controlled ventilation

The performance of gravity-based ventilation should be monitored particularly in moisture-prone areas such as bathrooms and kitchens. If the mirror remains fogged for a long time after a shower, the ventilation is likely too weak.

A building's pressure balance is a key factor for indoor air quality and structural durability. Ideally, the dwelling should be slightly under negative pressure relative to the outside, so that moist indoor air cannot penetrate into the structures. A suitable negative pressure is 0 to 5 pascals.

• Excessive negative pressure (over 10 Pa): Causes a sensation of draft, draws contaminants from structures into the indoor air, and makes it difficult to open doors
• Positive pressure: Moist indoor air penetrates into structures and can cause moisture and mold damage
• Balanced: Air circulates in a controlled manner through valves without harmful pressure fluctuations

Pressure measurement is part of the ventilation adjustment work. The measurement ensures that there is no harmful positive or negative pressure in the dwelling, and airflows are adjusted as needed to correct the pressure balance.

Ventilation adjustment is relevant in many situations:

• After renovation: Changes to room layout or intended use affect airflow requirements
• After duct cleaning: Cleaning changes the flow resistance in the ducts, so valves should be readjusted
• Sensation of draft: A persistent draft sensation indicates an imbalance between supply and exhaust airflows
• Moisture problems: Bathroom moisture does not clear normally or windows fog up easily
• New unit installation: Airflows must always be adjusted when replacing the air handling unit

Well-adjusted ventilation works unobtrusively — indoor air stays fresh, moisture does not accumulate, and energy consumption remains reasonable. The cost of adjustment work is a small investment compared to the problems that incorrect airflows can cause in the long run.