CFM — cubic feet per minute — is the unit US fan and blower ratings speak, where European AHU datasheets use m³/h and ventilation codes use L/s. The bridge factors are published in NIST SP 811 Appendix B: 1 CFM = 4.719474×10⁻⁴ m³/s, which makes 1 CFM ≈ 1.699 m³/h and CFM = L/s × 2.11888. A 1,000 CFM ERV is therefore about 1,699 m³/h or 472 L/s on a European commissioning sheet, and the arithmetic scales linearly — a 100 CFM supply diffuser is roughly 170 m³/h.
Ventilation requirements land in this unit at the end of a standard’s procedure. Under ASHRAE 62.1 the required outdoor air is Q = Rp × occupants + Ra × floor area: a 50 m² office for 10 people (Rp = 2.5, Ra = 0.3 L/s) needs 2.5 × 10 + 0.3 × 50 = 40 L/s — about 85 CFM — and dividing the flow by the room volume turns the same number into ACH for a per-space check.
One caution keeps CFM honest: it is a volume flow at the conditions where it is measured. Comparing an airflow at duct conditions with a standard-condition rating (SCFM) requires a density correction, not a unit conversion — the same m³/h is a different mass flow at a different temperature. Flow is also a magnitude, not a signed quantity, which is why converters reject negative entries as sign mistakes.