Calculator Inputs
Example Data Table
| Scenario | Size | Target | Margin | Output |
|---|---|---|---|---|
| Drywall sanding area | 30 ft × 20 ft × 10 ft | 8 ACH | 15% | ~920 CFM (combined) |
| Paint touch-up room | 8 m × 5 m × 3 m | 10 ACH | 10% | ~1320 m³/h (ACH) |
| General fit-out zone | 40 ft × 25 ft × 12 ft | 6 ACH | 10% | ~1320 CFM (ACH) |
Example outputs are rounded and depend on the selected method.
Formula Used
- Room volume: V = L × W × H
- Floor area: A = L × W
- ACH method airflow: Q = (V × ACH) / 60 (for CFM) or Q = V × ACH (for m³/h)
- People + area airflow: Q = (Occupants × Rateperson) + (Area × Ratearea)
- Safety margin: Qfinal = Qbase × (1 + Margin/100)
- Fan count: Fans = ceil(Qfinal / FanCapacity)
Combined mode selects the larger base airflow before applying margin.
How to Use This Calculator
- Select the unit system used on your site documents.
- Enter length, width, and height for the work zone.
- Set a target ACH based on the task intensity.
- Add occupants and optional rates for dilution guidance.
- Choose combined mode when uncertainty is high.
- Apply a margin to cover losses and dirty filters.
- Press calculate and review airflow plus fan quantity.
- Use export buttons to keep a shareable record.
Ventilation targets for temporary construction spaces
Air exchange planning protects crews when dust, fumes, or moisture rise quickly. Many tasks need higher dilution than normal occupancy spaces. Use the calculator to translate a target air change rate into airflow for the exact room volume. Add a safety margin to cover filter loading, duct losses, and imperfect mixing. For enclosed basements or interior buildouts, plan access paths for supply and exhaust to prevent short circuiting. Include temperature, humidity, and noise considerations when selecting equipment. These factors affect comfort, drying time, and worker acceptance on the site.
Choosing ACH versus occupancy based airflow
ACH is useful when contaminants scale with surfaces and processes, such as sanding or cutting. Occupancy plus area rates help when bioeffluents and general background sources dominate. In combined mode the calculator selects the larger base airflow, reducing under-ventilation risk. If your specifications cite a standard rate per person and per area, enter those values and compare against the ACH method to document your basis.
Accounting for contaminant generation and capture
Ventilation is strongest when paired with source control. Where possible, capture dust at tools, isolate mixing zones, and keep doors closed to limit spread. If a process produces bursts of emissions, consider increasing ACH for the active period and lowering it during idle time. The fan count estimate helps you plan modular equipment so airflow can scale up during peak work.
Fan sizing, distribution, and practical constraints
Select fan capacity that reflects real delivered flow, not nameplate only. Long ducts, bends, and filters can reduce airflow significantly. Distribute multiple smaller fans to improve coverage and to maintain redundancy. Place exhaust near the source when contaminants are heavier or localized, and provide make-up air to avoid excessive negative pressure that can backdraft appliances or pull in unconditioned air.
Documentation, commissioning, and ongoing verification
Record dimensions, method, margin, and final airflow in your site log. After setup, verify with anemometer readings or hood measurements at grilles, then adjust as work zones change. Re-check after filter changes and when partitions move. Export the report to share with safety teams and inspectors, and keep a consistent approach across rooms and shifts.
FAQs
What does “ACH” mean in this calculator?
ACH is air changes per hour. It is how many times the room’s air volume is replaced in one hour. Higher ACH typically means better dilution for dust, fumes, and moisture.
When should I use combined mode?
Use combined mode when you have both a process target and people based guidance. The calculator selects the larger base airflow, then applies your safety margin for a conservative requirement.
How do I choose a safety margin?
Start with 10% to 20% for temporary setups. Increase it when ducts are long, filters load quickly, or mixing is poor. Keep it practical so equipment and power limits are respected.
Why is my required airflow higher than my fan rating?
Fan ratings are often at free air conditions. Real installations add losses from ducting, grilles, filters, and bends. Use measured delivery when possible, or add margin and consider multiple fans.
Can I size fans for a partial shift or short task?
Yes. Set an ACH that matches the active work period and verify the setup. For short high emission tasks, higher airflow during the task can reduce exposure compared with a constant low rate.
Does this replace professional ventilation design?
No. It is a planning and documentation tool. For hazardous substances, confined spaces, or regulated exposures, follow applicable standards and consult qualified ventilation or safety professionals.