Ventilation design
Design greenhouse ventilation that adapts to every season
Understand natural and mechanical airflow, calculate fan capacity, and maintain vents so your plants stay productive year-round.
Ventilation system options
Natural ventilation
Relies on wind and buoyancy. Ridge vents exhaust hot air, while side vents or roll-up sides admit cooler air. Effective when vent openings equal 15–20% of floor area.
Mechanical ventilation
Uses powered fans to pull air through the greenhouse. Requires matched intake shutters and fan capacity sized to air volume and heat load.
Hybrid systems
Combine natural vents with supplemental fans to handle extreme weather while keeping energy use low.
Fan sizing quick-start
- Calculate greenhouse volume (length × width × average height).
- Determine desired air changes per minute (1.0 for warm climates, 0.75 for mild conditions).
- Multiply volume by air changes to find required fan capacity (CFM). Split capacity between multiple fans for redundancy.
- Size intake shutters or louvers to match fan CFM with minimal static pressure.
Seasonal ventilation strategy
Spring
Check vent openers and fans before the first warm spell. Transition from passive winter circulation to active ventilation as sun angle increases.
Summer
Run vents and fans together with shade cloth and evaporative cooling to keep temperatures below 86°F (30°C). Increase air changes to offset humidity.
Fall
Gradually reduce fan run times as nights cool. Maintain gentle circulation to prevent condensation without overcooling the structure.
Winter
Keep vents mostly closed but cycle fans periodically to refresh air and prevent stratification. Monitor humidity and use short heat-and-vent cycles to drop excess moisture.
Ventilation maintenance checklist
- • Clean vents, louvers, and fans every month during high-use seasons to remove dust and algae.
- • Lubricate hinges and moving parts on vents and automated openers twice per year.
- • Inspect belts, bearings, and motor mounts for wear; replace as needed before peak season.
- • Test thermostats and controllers quarterly to ensure they activate vents and fans at the correct setpoints.
Frequently Asked Questions
How do I know if my vents are large enough?
Measure total vent opening area. If it is less than 15% of floor area, add additional vents or roll-up sides. Monitor internal temperatures on sunny days; if they exceed outside temperatures by more than 10°F (6°C), increase ventilation capacity.
What if I can’t install large fans?
Use multiple smaller fans distributed along the sidewalls to achieve the required total CFM. Combine with natural ventilation to reduce mechanical load.
Do I need backup power?
Yes for mechanical systems. Install battery backups or generators so fans and controllers continue operating during outages, especially in hot climates.