Ventilation Rate Calculator

Calculator Inputs

Room name

Dimension unit

Target ACH (1/h)

Length

Width

Height

Direct room volume

Direct volume unit

Direct floor area

Direct area unit

Occupants

Outdoor air per person (m³/h·person)

Outdoor air per area (m³/h·m²)

Contaminant generation (m³/h)

Indoor concentration limit (ppm)

Outdoor concentration (ppm)

Safety factor (%)

Existing fan flow (m³/h)

Operating hours per day

Example Data Table

Scenario	Volume (m³)	Area (m²)	Target ACH	Occupants	ACH Flow (m³/h)	Occupancy Flow (m³/h)	Dilution Flow (m³/h)	Final Flow with 10% Safety (m³/h)
Example Lab	288.00	96.00	6.00	15	1,728.00	403.80	34.48	1,900.80
Small Workshop	180.00	60.00	8.00	8	1,440.00	218.00	50.00	1,584.00
Office Zone	240.00	80.00	4.00	20	960.00	524.00	27.78	1,056.00

These rows illustrate how the governing method controls the final airflow before the safety factor is applied.

Formula Used

V = L × W × H

Q_ACH = V × ACH

Q_occ = (N × R_p) + (A × R_a)

Q_dilution = G ÷ ((C_i - C_o) / 1,000,000)

Q_final = max(Q_ACH, Q_occ, Q_dilution) × (1 + Safety/100)

ACH_effective = Q_final ÷ V

Here, volume is in m³, area is in m², airflow is in m³/h, contaminant generation is in m³/h, and ppm values are converted into a dimensionless concentration difference for dilution sizing.

How to Use This Calculator

Enter room dimensions in meters or feet, or type a direct volume and floor area.
Set the target ACH for mixing or cleanliness performance.
Enter occupancy airflow rates to account for fresh air demand from people and floor area.
Add contaminant generation and concentration limits when dilution control matters.
Apply a safety factor, compare with existing fan capacity, and review the graph and export files.

FAQs

1) What is ventilation rate?

Ventilation rate is the airflow needed to replace or dilute indoor air. It is usually expressed in m³/h, L/s, or CFM, depending on design practice and equipment data.

2) Why compare ACH, occupancy, and dilution methods?

Each method protects a different requirement. ACH targets mixing, occupancy covers fresh air for people, and dilution limits pollutant concentration. The largest airflow is usually the safest design basis.

3) What does ACH mean?

ACH means air changes per hour. A value of 6 ACH means a volume of air equal to the room volume moves through the space six times each hour.

4) When is the dilution equation useful?

Use dilution when you know how much contaminant is generated and the maximum indoor concentration allowed. It is useful for tracer gases, fumes, and simple mass-balance estimates.

5) Why add a safety factor?

A safety factor accounts for leakage, imperfect mixing, changing occupancy, filter loading, and uncertainty in assumptions. It gives margin so real operation stays closer to the target.

6) Can I use feet instead of meters?

Yes. Choose feet for dimensions or ft³ and ft² for direct values. The calculator converts everything internally and reports final airflow in standard engineering units.

7) What if ACH and occupancy results disagree?

Use the higher airflow unless your design standard states otherwise. The larger value better protects the controlling condition, whether that is fresh air demand or room mixing.

8) Does this calculator size ducts or fans completely?

No. It estimates required airflow only. Final fan selection also needs pressure loss, filter resistance, noise limits, duct layout, and efficiency checks.