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Air ventilation
airflow calculator
Calculate airflow through a door gap, transfer air grille, vent, or make-up air opening. The calculator has three modes: room-by-room sizing according to D2/FINVAC guidelines, single-room verification, and direct calculation using the orifice equation.
How does the calculator work?
The calculator is based on the orifice equation: Q = Cd · A · √(2·Δp / ρ), where Cd is the discharge coefficient, A is the free area of the opening, Δp is the pressure difference, and ρ is air density. In practice, you enter the opening dimensions and the pressure difference, and the calculator tells you how much air flows through the opening.
In room-by-room mode, the calculator automatically calculates each room’s airflow requirement according to D2 and the FINVAC 2018 sizing guideline. In supply-air rooms (bedroom, living room, study), the requirement is calculated in two ways—by floor area (0.5 dm³/s per m²) and by number of occupants (6 dm³/s per person)—and the higher value is used. In extract-air rooms (kitchen, bathroom, WC), D2’s fixed extract airflow rates are used.
The results are indicative. Actual flow is affected by wind, temperature differences, room layout, and the opening’s location. The calculator’s accuracy is approximately ±15–25%.
Do you want an accurate assessment for your property?
The calculator provides direction, but accurate numbers can only be obtained by measurement. An air ventilation survey (from €248) is a 30-minute visit where we assess the situation on site and determine what should be investigated further. The survey fee is credited if you order follow-up work.
