Greenhouses are designed to trap heat and create stable growing environments. During warmer months, this can quickly lead to excessive temperatures and high humidity. Ventilation plays a key role in exchanging warm, stale air for cooler, fresh air and maintaining balanced conditions.
Ventilation is a plant health tool, not just a way to cool a greenhouse. It affects temperature, humidity and airflow through the crop zone, which influences disease pressure and plant performance. Just like measuring pH and EC helps you manage the root zone, understanding ventilation helps you manage the climate zone. Below are eight common questions growers ask about greenhouse ventilation.
1. What are weather stations and why do I need one?
Regardless of the automation system you choose, a weather station is a critical component. Weather stations collect data from outside the greenhouse, including temperature, humidity, solar radiation, rainfall, and wind direction.
This external data works alongside internal sensors that monitor the greenhouse microclimate. Together, they help growers make informed decisions about when and how to ventilate.
Points to consider:
- Install the weather station in an accessible location for regular cleaning
- Keep sensors clear of debris such as leaves, dust, or bird droppings
- Reliable data depends on robust, accurate sensors that can withstand outdoor conditions
2. What are greenhouse roof vents?
Roof vents are a passive cooling method that relies on natural convection. Warm air rises and exits through the roof vents, drawing cooler air in from below.
Roof vents are particularly effective in temperate climates and can be adjusted to either release heat or retain warmth as needed. Common roof vent designs include open-panel, retractable-film, flat-roof, and low-profile systems.
Points to consider:
- Using cooler outside air during warm conditions is cost-effective
- Roof vents help maintain temperature and humidity setpoints
- Open roof structures increase natural light levels
- Mesh screens can reduce pest entry but may limit airflow by up to 45%
3. What are side vents?
Side vents increase airflow while helping protect crops. In bench-based growing systems, sidewalls can be rolled up to bench height, allowing cool air to flow beneath the plants.
Side vents reduce reliance on fans and electrical systems, making them a cost-effective ventilation option. Research has shown that combining roof and side vents delivers the most effective airflow, particularly in warm, low-altitude climates.
4. What is buoyancy-driven ventilation?
Buoyancy-driven ventilation occurs when differences between indoor and outdoor temperatures create airflow. Warm air rises due to lower density, creating upward movement similar to a chimney effect.
Advantages include:
- Does not rely on wind
- Provides relatively stable airflow
- Allows control over air intake locations
Limitations include:
- Depends on sufficient temperature differences
- Outside air quality can affect greenhouse conditions
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Performance is influenced by greenhouse design
5. What is wind-driven ventilation?
Wind-driven ventilation occurs when pressure differences form between the windward and sheltered sides of a greenhouse. Air naturally moves from high-pressure to low-pressure areas.
This method works best when vents are positioned to take advantage of prevailing winds. Wind-driven ventilation is less effective if roof vents are not complemented by side vents.
Points to consider:
- Greenhouse length and layout affect airflow efficiency
- Wind conditions vary throughout the day and season
6. What size should roof and side vents be?
According to the American Society of Agricultural and Biological Engineers, roof vent area should equal the combined sidewall vent area. Each should account for at least 15–20% of the greenhouse floor area.
7. Where should vents be placed?
Roof vents are typically hinged along both sides of the ridge. Side vents are usually positioned at bench height to encourage airflow across the crop zone.
8. Why is greenhouse height important?
Taller greenhouses are generally easier to ventilate. Increased height enhances the buoyancy effect, allowing warm air to rise above the crop canopy and exit more efficiently.
In regions with consistently high heat and humidity, natural ventilation alone may not be sufficient. Additional airflow or extraction systems may be required to maintain stable conditions.
Related greenhouse climate topics
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Knowing when to ventilate is just as important as having vents.
Bringing outside air into a greenhouse can stabilise conditions or make them worse depending on temperature, humidity, and wind. Bluelab helps growers monitor both internal and external conditions so ventilation decisions are based on real data, not assumptions.
Contact Bluelab to discuss monitoring and measurement options for your grow environment.
