Greenhouse Ventilation Calculator
Exhaust fan sizing for a greenhouse.
Enter your values
ⓘ Live results
Results
- Summer exhaust
- 2,304 CFM
- Winter minimum (2 CFM/sq ft)
- 576 CFM
- Floor area
- 288 sq ft
- Intake louvre area
- 4.6 sq ft
- Suggested fans
- 1 unit(s)
Quick answer
A greenhouse typically needs 8-12 CFM per square foot of floor in summer, corrected for altitude and shading.
CFM = area x 8 x altitude factor / shade factor
How to use the Greenhouse Ventilation Calculator
- 1Measure the greenhouse footprint.
- 2Add altitude and any shade cloth already fitted.
- 3Size intake louvres at roughly 1.25 times the fan area so the fans are not starved.
Worked example
Using the values the calculator loads with:
Inputs
- Length24 ft
- Width12 ft
- Altitude0 ft
- ShadingNo shade cloth
Results
- Summer exhaust2,304 CFM
- Winter minimum (2 CFM/sq ft)576 CFM
- Floor area288 sq ft
- Intake louvre area4.6 sq ft
- Suggested fans1 unit(s)
Frequently asked questions
Two-speed fans?
Yes — a low speed near 2 CFM per sq ft handles spring and autumn without chilling plants.
Where do fans go?
Exhaust at one gable end, intake louvres at the opposite end for end-to-end sweep.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.