Garden Fan Sizing Calculator

Dial in airflow fast for healthier garden spaces. Account for altitude, filters, and ducting losses. Pick a fan size that matches your target conditions.

Calculator Inputs

Switching updates labels and recommended defaults.
Choose ACH for general ventilation; heat removal for strict temperature control.
Used for selection guidance (not a pressure model).
Use average height for sloped roofs.
Typical: 6–12 ACH for greenhouses; higher for enclosed rooms.
Include lights, pumps, and sun gain estimates.
Smaller rise requires more airflow.
Covers seasonal peaks and uncertainty.
Filters, louvers, bends, screens, and grills.
Converts required delivery to catalog rating.
Higher altitude reduces air density and fan delivery.
Per-fan sizing uses operating fans only.
Used to estimate a practical fan diameter.
Enter per-fan rating to estimate achieved air changes.

Formula Used

Air changes method
  • Volume = Length × Width × Height
  • Base CFM = Volume(ft³) × ACH ÷ 60
  • Base m³/h = Volume(m³) × ACH
Heat removal method
  • CFM = BTU/hr ÷ (1.08 × ΔT°F)
  • m³/h ≈ (2.985 × Watts) ÷ ΔT°C
  • Then apply safety, losses, altitude, and efficiency factors.
Final airflow
Required = Base × Safety × Loss × Altitude ÷ Efficiency
Altitude factor uses a density-ratio approximation: ρ/ρ0 ~ exp(-h/8434).

How to Use This Calculator

  1. Pick your unit system and sizing method.
  2. Enter the space dimensions using average height.
  3. Set ACH or enter heat load and allowed temperature rise.
  4. Add safety margin, loss allowance, and site altitude.
  5. Choose installed and spare fan counts for per-fan sizing.
  6. Review total airflow, per-fan airflow, and suggested diameter.
  7. Export CSV or PDF for purchasing and documentation.

Example Data Table

Scenario Space Method Inputs Estimated required airflow Suggested fan size
Small greenhouse 20×12×8 ft ACH 8 ACH, 15% safety, 10% losses ≈ 3,700 CFM ≈ 24 in axial
Grow tent room 4×3×2.2 m Heat 1200 W, ΔT 6°C, 15% safety ≈ 690 m³/h ≈ 315–355 mm inline
Filtered shed 16×12×9 ft ACH 10 ACH, 20% safety, 25% losses ≈ 4,500 CFM ≈ 30 in, higher pressure
Examples are illustrative; always check fan curves and resistance.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.