Supply Air

Supply air is the fresh outdoor air that is filtered, conditioned, and ducted into a building's living spaces by the ventilation system. In a mechanical supply and exhaust ventilation system, supply air passes through the air handling unit where it is filtered to remove particles, heated (usually via the heat recovery cell), and distributed through ducts to bedrooms, living rooms, and other occupied spaces.

The quality and volume of supply air directly determine indoor air quality. Finnish building codes require a minimum ventilation rate of approximately 0.5 air changes per hour for residential buildings, which translates to roughly 6 liters per second per person. Inadequate supply air leads to elevated carbon dioxide levels, excess humidity, stale odors, and an increased risk of condensation and mold in structures.

Supply air should be delivered to rooms where people spend the most time, while exhaust is extracted from rooms that generate moisture and contaminants (kitchens, bathrooms). This creates a controlled airflow pattern from clean spaces to dirty spaces, ensuring that pollutants are carried out of the building rather than spread through it.

If rooms feel stuffy despite the ventilation being on, the supply air volume may be insufficient or the airflow may be out of balance. Common causes include clogged filters, blocked diffusers, or incorrectly adjusted dampers. A ventilation professional can measure and adjust supply air volumes to meet design specifications and restore comfort.