HVAC & Energy

Air Changes per Hour Calculator

Relate room dimensions and airflow to nominal air changes per hour. Compare SI/US results and review the method, assumptions and related references below.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

Inputs

Solve forPreset

Room length

Room width

Room height

Air volume flow

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YOUR CALCULATION

Results

Air changes per hour

7.2 h⁻¹

Volume flow

100 L/s6,000 L/min360 m³/h1,585.0323 GPM (US)211.888 CFM

Room volume

50 m³1,765.7333 ft³

Nominal one-volume time

8.3333 min

Room volume and nominal air changes per hour · schematic, not to scale

Calculation breakdown

Result interpretation: Relate room dimensions and airflow to nominal air changes per hour

Assumptions & checks

Use the relevant outdoor, exhaust or filtered airflow explicitly; recirculation is not automatically fresh air. Nominal turnover is not infection clearance or code compliance.

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Formula

Relate room dimensions and airflow to nominal air changes per hour

ACH=Q(m³/s)×3600/Vroom; Q=ACH×Vroom/3600. Nominal turnover=60/ACH minutes. Worked example: A 5×4×2.5 m room has volume 50 m³; 100 L/s gives 7.2 ACH and 8.333 minutes per nominal volume.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Room length: 5 m
Room width: 4 m
Room height: 2.5 m
Air volume flow: 100 L/s

Result

Air changes per hour: 7.2 h⁻¹
Volume flow: 100 L/s
Room volume: 50 m³
Nominal one-volume time: 8.3333 min

Technical references for this calculation

Reference lookupDry Air Properties Table Reference lookupRound Duct CFM Chart

Frequently asked questions

What does this result tell me?

Use the relevant outdoor, exhaust or filtered airflow explicitly; recirculation is not automatically fresh air. Nominal turnover is not infection clearance or code compliance.

How can I check the calculation?

Worked example: A 5×4×2.5 m room has volume 50 m³; 100 L/s gives 7.2 ACH and 8.333 minutes per nominal volume. Review each stated input and unit; use project-specific values rather than treating the editable example as a requirement.

Reference data & method sources

CDC/NIOSH ventilation terminology
Volumetric airflow per room volume expressed per hour. No health or ventilation-code recommendation is calculated.
NIST SI conversion factors
SI/US dimensional conversions. Geometry and energy balances are stated explicitly, not attributed to a design standard.