Where Should Circulation Fans Be Placed in a Greenhouse?


Ventilation extends your growing season while protecting plants from insects that threaten them, and also decreases thermal stress and condensation on walls and ceilings. Best way to find the Greenhouse Ventilation Exhaust Circulation Fans.

Greenhouse fans should be strategically installed and sized to ensure even air circulation and temperatures throughout. Their location should match with prevailing summer winds for optimal efficiency.

Ceiling Vents

Proper ventilation placement can make a big difference in the efficiency of greenhouse circulation systems. Roof vents should be set opposite one another while side vents should be located near the base of walls to promote cross-ventilation and allow cool air to freely enter, escape excess heat, circulate throughout, and revitalize plants in your greenhouse structure. This provides optimal temperature regulation as well as refreshing breezes that stimulate plant life.

In the summer months, vents should be placed near plant canopy height for optimal cooling results; this enables fresh outside air to move upwards more readily than warm greenhouse air and reach the ceiling, providing an inflow of new air into your greenhouse. However, during winter conditions they should be situated closer to ground level to prevent warm air being drawn back in.

As part of your ventilation system, the intake louvers mustn’t become blocked by vegetation or structures within your greenhouse. A louver area at least half as large as that of your fan size should facilitate air exchange – this helps eliminate pockets of high humidity in addition to decreasing fungal diseases that develop when moisture stays on leaf surfaces or the frame itself.

A steady airflow in your greenhouse is critical to optimizing plant growth because it prevents excess moisture and heat build-up on leaf surfaces that could otherwise inhibit photosynthesis. Furthermore, moving air reduces relative humidity levels within the canopy as well as plant surface surfaces while also maintaining gas exchange between boundary layer air and the outside air.

Constant air movement also serves to control the temperature in your greenhouse, making it particularly useful during the winter. Furthermore, this movement helps keep plant leaves, stems and fruit cool to prevent damage caused by freezing temperatures.

Before heating season starts, to ensure your ventilation system is functioning as designed, take time to assess its static pressure with a manometer and ensure it falls between 0.03 to 0.13 inches – any reading over this could indicate problems with either vents themselves or inadequate makeup air supply.

Side Vents

Ventilation fans in greenhouses increase air movement, helping maintain consistent temperatures throughout and decreasing heat loss. Cooled and moistened air also cools plants down while protecting them from diseases, mildew, and insect pests; while evaporative cooling produced by ventilation fans can also help decrease summer temperatures in the greenhouse. Ventilation fans are especially beneficial in regions with strong winds or when rain or snow prevents the opening of the roof of the greenhouse.

The location and size of the intake louver play an essential role in the performance of any system. Fans should be designed to produce one volume of air change per minute in a greenhouse with an 8-foot height and should aim to raise temperatures approximately 10 degrees lower than the outside temperature.

Side vents should be placed near the base of a wall for better airflow and natural convection, creating a balanced ventilation system across all areas of a greenhouse. When combined with roof vents, these create an effective system.

Louvers constructed of poly-covered or glass should provide the appropriate amount of airflow for each fan. Their operation should be managed via motorized dampers or solenoids connected to each thermostat that operates each fan, although small, tight houses often experience negative pressure quickly when their fan turns on, which in turn causes their louver to close due to negative pressure caused by negative airflow and can damage greenhouse plants or prevent fans from functioning correctly.

Another popular form of ventilation is using natural systems that rely on buoyancy to move air, with wind speed providing the exchange of internal and external air. Although such methods work effectively for most weather conditions, achieving adequate airflow may prove more challenging when low humidity levels exist or when winds blow in an opposite direction to what would normally be ideal during summer ventilation.

Selecting a combination of roof, end, and side vents that provides adequate ventilation of your greenhouse in most weather conditions will enable you to effectively ventilate it. However, it is also crucial that you monitor its conditions regularly and adjust as necessary; thermometers, hygrometers, and carbon dioxide sensors allow you to track temperature, humidity, and CO2 levels within your greenhouse for efficient monitoring and adjustment of ventilation strategies accordingly.


Many greenhouse owners choose to implement a powered ventilation system in their greenhouse, and louvers on both walls act as fans to circulate air throughout. The louvers help create an even temperature distribution while simultaneously decreasing humidity pockets; motorized versions with flanged seals may provide the best seal, which also works great if using thermostatically-controlled fans that turn themselves on when the set point has been reached.

To achieve optimal fan airflow systems in greenhouses, it is suggested that exhaust and circulation fans have a combined total capacity that exceeds two times the floor area of the greenhouse. If you are growing tall crops or hanging baskets, additional capacity may be necessary due to additional turbulence created. Louvers should be sized appropriately to match this capacity of the fan system and placed either above the crop canopy or along sidewalls depending on growing space size and evaporation rates during your growing season.

Ventilation systems that utilize roof and side vents with louvers can be equally effective, provided they are sized appropriately. In a greenhouse measuring 150 feet long, fans should be placed at one end wall while louvers at the other to allow them to align with prevailing summer winds for maximum effectiveness. Longer greenhouses should incorporate fans at both ends to provide replacement air while encouraging even air movement throughout.

A greenhouse’s fans should be set to rotate every eight minutes to achieve maximum efficiency, helping prevent overheating of its crops and promote plant growth. Along with proper fan sizing, weather conditions must also be closely monitored so you can adjust ventilation strategies as necessary; during hot and sunny days it is recommended that vents be kept open to release extra heat through natural convection; at night however, they should close to conserve warmth and avoid overheating.

Exhaust Fans

Location is of critical importance in greenhouse ventilation. A fan too far from either end will struggle with working against summer winds to pull air out and cool the greenhouse effectively. Ditto for any doors opening into or near any fan; for instance, a single-span hoop house with vents at one end and fans at the other will only work effectively as long as any open doors remain. Air travels the path of least resistance, meaning an exhaust fan could only cool the first few feet of the greenhouse.

Fans that work well with natural ventilation systems typically feature high CFM (cubic feet per minute) ratings, designed to move enough air each minute to replace what has been lost, thus maintaining even temperature distribution and decreasing humid pockets in your greenhouse. This type of passive ventilation is perfect for greenhouses located in temperate climates as it saves growers time opening and closing vents manually.

For optimal active ventilation, you will require intake and exhaust fans connected to a thermostat that is designed to turn on when desired greenhouse temperatures are reached. They’re typically installed in one end wall ridge’s ridge crest ridged ridged ridged ridged wall’s ridge crest that draws air through continuous louvers attached to motorized dampers or solenoids for proper performance.

Fans rated for CFM should be sized to provide at least one air exchange per minute to avoid stale air buildup in a greenhouse and protect plants from fungal diseases and pests that thrive in moist, stagnant air. A ventilation system designed for your greenhouse volume should generate at least one complete air change within 10 minutes; additionally, the intake louver area should be at least 1.25 times the fan area to achieve more even temperatures, particularly poly-covered greenhouses. It is important to conduct periodic checks of your ventilation system, as stale air can collect in areas not properly ventilated. Regular checks on this component will prevent buildup in areas not properly being ventilated – inspection should take place as this preventable buildup could occur otherwise.