Air changes (ACH) calculator
Room volume × air-change rate = required airflow. Enter dimensions or a volume directly, then pick a room type from a common international reference list (IMC / ASHRAE 170 values) or Poland's detailed PN-83/B-03430 / Dz.U. table — or just type your own ACH.
How to use this calculator
- Choose the input method — room dimensions, or a volume directly.
- Enter the room size, or its volume.
- Pick a room type from the reference list to auto-fill typical ACH values, or enter your own supply/extract ACH.
- Add a safety margin if you want one built into the airflow.
- Read the required airflow in your chosen display unit.
What this calculates
Air changes per hour (ACH) is simply how many times the entire volume of a room is replaced with (theoretically) fresh air in one hour. Once you know a room's volume and the air-change rate it needs, the required airflow follows directly:
V̇ = V × ACH
V̇ = required airflow, m³/h
V = room volume, m³
ACH = air changes per hour, h⁻¹
That's the entire calculation — the only real engineering judgement is picking the right ACH for the room in question, which is what the room-type list is for.
Where the room-type ACH values come from
The room-type dropdown has two source groups, kept clearly separate. "Common rooms — general guideline (international)" transcribes the widely published International Mechanical Code (IMC) Table 403.3.1.1 minimum-ventilation values and ASHRAE 170 (healthcare) figures, as republished across multiple HVAC references — not read from a licensed copy of either standard, so treat it as a widely-cited starting point rather than a verified code excerpt. The Poland-specific groups underneath aren't a new table either — they're read directly, at page load, from the same reference data used by our Ventilation Airflow Calculator: PN-83/B-03430 (Az3:2000) and the associated Dz.U. regulation citations, transcribed from the Venture Industries Group "Wentylacja i klimatyzacja — Pomoce projektowe" guide. Where a source publishes a range instead of a single figure, this tool fills in the midpoint as a starting point and states the full range in the note underneath — edit it if you have a more specific design figure.
Supply and extract are always shown separately, and are equal by default. A few Poland source-table room types (mostly laundry and industrial process rooms) specify a different air-change rate for supply than for extract, to keep the room under negative or positive pressure relative to its surroundings — picking one of those fills in both rates for you. You can also just type different supply/extract numbers yourself.
The optional safety margin adds a flat percentage on top of the volume × ACH result for both supply and extract — useful for covering duct leakage, filter loading, or simply not wanting to run right at the calculated minimum.