ACH to CFM calculator (room ventilation airflow)
Turn floor area, ceiling height, and target air changes per hour (ACH) into CFM plus m³/h and L/s for fan and duct rough sizing. This page answers ventilation volume turnover, not cooling tons—use it before detailed outdoor-air or contaminant models.
Input parameters
Quick examples:
About this calculator
Estimates bulk airflow from geometry and ACH so you can compare fan duty across warehouses, workshops, and retrofit zones. For cooling and heating kW/ton block loads, use the HVAC Capacity Calculator. Browse all HVAC tools on the HVAC Calculators Hub.
Calculation results
What you are seeing: total airflow if the entire room volume were turned over at the ACH you typed. Not modeled: duct leakage, heat recovery, variable-volume turndown, zonal mixing, or minimum outdoor-air fractions. Next: use HVAC Capacity for tonnage/kW, or Industrial Energy Estimator once you have motor kW.
Professional disclaimer
This calculator provides preliminary airflow estimates only. For final ventilation design, contaminant control, and compliance with local building codes, consult a licensed mechanical engineer or certified industrial hygienist.
ACH screening bands (conceptual)
Use project-specific criteria; the table is for classroom-style triage only—not a code extract.
| Space | Typical screening ACH (broad) |
|---|---|
| General office (comfort turnover) | 4–8 |
| Warehouse (full volume rarely mixed) | 1–4 |
| Light workshop / fab bay | 6–12 |
Scenario snapshots (volume vs ACH)
- 200 m² × 4 m = 800 m³ at 6 ACH → about 2,830 CFM continuous equivalent if the full volume participates—click Quick example to load.
- High-bay warehouse: if only the lower 4 m are actively mixed, reduce effective volume before trusting ACH-driven CFM.
- Containment or fume hood labs: ACH alone is insufficient; stop at this tool and use controlled exhaust design methods.
Formula & explanation
Volume V = area × height (m³). Hourly airflow Qm³/h = ACH × V. Then
CFM = Qm³/h ÷ 60 × 35.3147 and L/s = Qm³/h ÷ 3.6.
This page vs HVAC Capacity: here you set how often the room volume turns over; there you estimate sensible/latent block energy (kW, tons). They are complementary checks in early design.
Guides: HVAC sizing guide · How to calculate HVAC capacity · HVAC Calculators Hub
Frequently asked questions
What does ACH mean in HVAC?
ACH counts how many times the room’s total air volume is replaced per hour under the scenario you assume. It helps communicate purge and general ventilation concepts but does not, by itself, define compliant minimum outdoor air.
How do you convert ACH to CFM?
Compute volume in cubic meters, multiply by ACH for m³/h, divide by 60 for m³/min, then multiply by 35.3147 to get CFM. This page automates that chain from area and height.
What ACH is typical for warehouses versus offices?
Offices often use higher turnover numbers in early narratives than tall warehouses where only part of the volume is conditioned or destratified. Treat any default ACH as a stakeholder placeholder until standards and risk review lock it in.
Does this calculator replace ASHRAE 62.1 outdoor air calculations?
No. Code and ASHRAE procedures combine people, area, zone type, and filtration. Use this tool only for ACH-driven bulk airflow from the volume you enter.
How is CFM related to m³/h and L/s?
Cubic meters per hour equals CFM times 1.699010796. Liters per second equals cubic meters per hour divided by 3.6. The results block lists all three for cross-border equipment datasheets.