Ventilation ACH Calculator
Air changes per hour your current fan/AHU actually achieves in a space.
Measure Q at the grilles, not the fan rating — duct leakage commonly steals 20–30% between the two.
Formula
Ventilation ACH Calculator is a free ach calculator for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Ventilation ACH Calculator
Air changes per hour your current fan/AHU actually achieves in a space. The calculation implements ACH = Q(m³/h) / V_room (ASHRAE 62.1; CDC ventilation guidance). Measure Q at the grilles, not the fan rating — duct leakage commonly steals 20–30% between the two.
How to use Ventilation ACH Calculator
- 1Enter Airflow delivered in L/s.
- 2Enter Space volume in m³.
- 3Read Air changes per hour instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Ventilation ACH Calculator?
- ✓Implements the standard formula — ACH = Q(m³/h) / V_room
- ✓Reference cited on-page: ASHRAE 62.1; CDC ventilation guidance
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Built-in engineering verdict flags out-of-range results instantly
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Ventilation ACH Calculator use?+
It computes ACH = Q(m³/h) / V_room, per ASHRAE 62.1; CDC ventilation guidance. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
Measure Q at the grilles, not the fan rating — duct leakage commonly steals 20–30% between the two.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Ventilation ACH Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
Related Engineering tools
Reynolds Number Calculator
Compute Re from density, velocity, pipe diameter and viscosity — with instant laminar/turbulent classification.
● LiveLaminar vs Turbulent Flow Classifier
Classify hydraulic-oil or process-fluid flow regime from kinematic viscosity, line velocity and tube bore.
● LiveBernoulli Equation Solver
Solve downstream pressure between two points from velocities, elevations and fluid density (ideal, lossless).
● Live