Greenhouse Ventilation / Fan Sizing Calculator
Estimate a summer exhaust-airflow target using the UMass floor-area and design-height method.
Your planning estimate
Enable JavaScript to run this calculator. The formula and assumptions are available below.
How this tool works
UMass describes a summer design target based on floor area × 8 ft × one air exchange per minute. The separate natural-vent reference is 15–20% of floor area for the combined side openings AND a matching ridge-opening area; it is not 15–20% shared between both.
Fan target CFM = floor width × floor length × design height × air changes per minute. No additional division by 60.
What this estimate does not tell you
Fan airflow must be checked at the actual system resistance, not only a free-air rating. Screens, louvers, shutters and inlets affect delivery. The natural-vent figures are a separate reference, not an equivalent mechanical fan design. Ventilation alone does not guarantee air below outdoor temperature. No wiring or installation specification is supplied.
Sources & verification
Manufacturer figures are reproduced as documented. Editorial comparisons and calculations are identified separately.
- UMass Extension — Ventilation for Greenhouses ↗ — checked 2026-09-19.
- UMass Extension — Natural Ventilation in Greenhouses ↗ — checked 2026-09-19.
Source pages can change. The supplier’s current exact-model documentation and local requirements control final decisions. Report a correction.