Greenhouse Fan Calculator
Determine exact CFM airflow and exhaust fan sizing required to vent heat, control relative humidity, and deliver fresh CO2.
Complete Ventilation Guide: Greenhouse Fan & CFM Calculator
Proper greenhouse ventilation is critical to regulating microclimate temperature, relative humidity, and carbon dioxide levels. Without adequate air movement, solar radiation rapidly overheats the enclosure, leading to heat stress, blossom drop, and rampant fungal infections like gray mold (Botrytis). Searching for a greenhouse fan calculator, greenhouse cfm calculator, greenhouse cfms calculator, greenhouse exhaust fan calculator, or greenhouse air flow calculator brings you to the essential engineering equations governing agricultural airflow.
The Standard Greenhouse Ventilation Formula
For warm summer conditions, agricultural extension guidelines recommend exchanging 1.0 to 1.5 times the total interior volume of air per minute. The core formula is:
Required CFM = House Volume (cu ft) × Desired Air Changes per Minute × Elevation Factor × Solar Gain Factor
Step-by-Step Volume Calculation
To compute interior volume for a gable greenhouse:
- Main Rectangular Block: Width × Length × Eave Height
- Triangular Roof Gable: 0.5 × Width × (Peak Height - Eave Height) × Length
- Total Volume: Add Rectangular Volume + Triangular Gable Volume
Matching Fan CFM to Intake Louvers
An exhaust fan cannot pull air effectively if air intake openings are restricted. Negative pressure starves fan motors and creates air resistance. Maintain a minimum of 1.25 to 1.50 square feet of motorized intake louver opening for every 1,000 CFM of exhaust capacity.
💡 Pro Circulation Tip: HAF Fans
In addition to exhaust fans, deploy Horizontal Air Flow (HAF) circulation fans inside the canopy moving ~2 to 3 CFM per sq ft of floor area. This breaks up leaf boundary air layers and ensures uniform CO2 distribution.