Inputs
Example data table
Sample inputs for quick testing.
| Scenario | Size | Occupants | ACH | Rp | Ra |
|---|---|---|---|---|---|
| Site office | 6×5×3 m | 6 | 6 | 10 | 0.3 |
| Workshop bay | 12×8×4 m | 10 | 8 | 10 | 0.6 |
| Training room | 10×7×3 m | 20 | 6 | 7.5 | 0.4 |
Adjust rates to match your local code or design guide.
Formula used
- Area A = L × W
- Volume V = A × H
- ACH method Q = (ACH × V) / 3600
- People + Area Vbz = Rp×P + Ra×A
- Effectiveness Voz = Vbz / Ez
- Credit Voz,adj = max(0, Voz − infiltration)
- Design Choose ACH, People+Area, or max.
Conversions: 1 m³/s = 2118.88 CFM, and 1 m³ = 1000 L.
How to use this calculator
- Choose your units and the calculation method.
- Enter room dimensions, occupants, and target ACH.
- Set Rp, Ra, and Ez from your design criteria.
- Add an infiltration credit only with justified data.
- Click Calculate to view airflow targets instantly.
- Download a CSV or PDF report for project records.
Ventilation targets used on job sites
Indoor ventilation planning supports worker comfort and contaminant control during construction and fit‑out. This calculator estimates required supply or exhaust flow and reports air changes per hour (ACH), outdoor air per person, and a simple carbon‑dioxide check. Use it to size temporary fans, ducts, and openings, and to document assumptions for safety meetings. It also helps coordinate with HVAC commissioning and ensures temporary ventilation does not conflict with fire protection or containment plans during active phases.
Air changes per hour and room dilution
ACH describes how many room volumes are replaced each hour. Higher ACH improves dilution of dust, VOCs, and moisture, but may increase heating or cooling demand. The calculator converts room volume from length, width, and height, then computes ACH from total airflow. Comparing ACH before and after changes helps verify whether added fan capacity meaningfully reduces risk.
Outdoor air per person and occupancy load
Occupancy strongly drives fresh‑air needs. The tool estimates outdoor air flow per person using your chosen standard rate and the current headcount. If the per‑person value is low, consider reducing occupancy, scheduling high‑emission tasks off‑hours, or increasing outdoor intake. For enclosed spaces, the CO₂ estimate highlights when breathing load can outpace ventilation.
Exhaust, make-up air, and pressure control
Balanced systems matter. Excess exhaust can pull fumes from adjacent areas, while excess supply can push dust into clean zones. The calculator summarizes net flow and indicates whether the space trends negative, neutral, or positive. Pair this with temporary barriers, local capture at sources, and filtration when outdoor air is limited by weather or security.
Interpreting results for safer indoor work
Treat results as engineering guidance, not a substitute for measurement. Confirm airflow with an anemometer, verify pressure direction with smoke, and monitor CO₂ or particulate levels when feasible. Recheck inputs when layouts change, doors are propped open, or new equipment is added. Document final settings and maintenance intervals for filters and fans.
FAQs
What does ACH mean in practical terms?
ACH is the number of room volumes replaced each hour. Higher ACH generally improves dilution of airborne contaminants, but it can increase energy use and drafts. Use ACH together with source control and filtration for best results.
Which airflow value should I enter, supply or exhaust?
Enter the dominant mechanical flow affecting the zone. If you have both, enter supply and exhaust separately so the calculator can report net pressure trend. For natural ventilation, estimate combined inflow through openings using measured or rated fan data.
How do I choose an outdoor air rate per person?
Start with your project’s specification or a recognized indoor air guideline. Higher rates are preferred for high‑density areas or odor‑producing tasks. When outdoor air is constrained, add local capture and high‑efficiency filtration to compensate.
Why does the calculator show a CO₂ estimate?
CO₂ is a convenient proxy for ventilation versus breathing load. Elevated CO₂ can indicate insufficient outdoor air for the current occupancy. It does not measure chemicals or dust, so use additional monitoring when those hazards are present.
What should I do if the space is predicted negative pressure?
Negative pressure is useful for dusty or odorous work zones, but it can draw pollutants from adjacent areas. Seal gaps, provide dedicated make‑up air, and verify direction with smoke. Keep doors controlled to maintain the pressure plan.
How often should I reassess ventilation during construction?
Reassess whenever occupancy changes, partitions move, weather conditions shift, or new emission sources appear. As a minimum, review weekly and after major schedule transitions. Record fan settings, filter changes, and any field measurements for accountability.