Where and How to Properly Place Fans in a Grow Tent or Grow Room

Precise climate control is the foundation of success in indoor cultivation. Still, the correct placement of fans is often an overlooked detail that can significantly affect the microclimate in the grow space. Air circulation influences plant growth as well as their resistance to diseases and pests. In this guide we will discuss the importance of fans, their effective placement, and add tips for growboxes and growrooms.

When cultivating plants indoors we use two basic types of fans, each for different purposes. Exhaust fans remove the “used” air from the grow space. The intake of fresh air can be passive or you can use a second fan for this purpose, which is especially useful in larger growrooms. Continuous air exchange helps maintain stable temperature and humidity in the cultivation area. A consistently optimal climate is important both for plant photosynthesis and as a prevention against mold and pest outbreaks.

Circulation fans placed inside the grow space are meant to mimic the natural wind that acts on plants outdoors and stimulates them to develop strong stems. Constant air movement also makes life harder for pests and discourages them from settling on plants. Properly placed circulation fans help prevent pockets of hot or cold air, for example under lights or in the corners of the growroom.

Types of fans for indoor cultivation

• Clip-on circulation fans are the most commonly used type. You can easily attach them to tent poles and they are most suitable for small or medium-sized growboxes.
• Stand oscillating fans are suitable for moving air in medium or large tents and growrooms. They take up a bit more space than the clip-on variant. They are usually larger and, thanks to oscillation, cover more cultivation area.
• Floor fans excel in high performance and are most often used in large growrooms to move air between aisles of plants. They can also be used in large tents. Be careful with strong airflow which can damage plants.
• Exhaust fans of various types are an indispensable part of every indoor growroom. Older models with an AC motor are noisier and consume more energy than newer models powered by an EC motor. Modern exhaust fan versions are easier to regulate and have a somewhat higher purchase price.

Fan placement in small grow tents

In small grow tents up to roughly 2 m² of cultivation area you will usually be fine with one exhaust fan and one circulation fan.

• Circulation fans should be placed in a corner of the tent 20–50 cm above the tops of the plants. The airflow should reach the top and middle parts of the plants. In a small space the fan may be very close to the leaves, so set it to a lower speed to avoid drying out the plants. For these purposes small clip-on fans with or without oscillation are sufficient.
• Additional circulation fans are usually not necessary in small grow tents. If you want, you can place a small fan near the base of the tent so the air is directed toward the lower parts of the plants. The substrate will dry out a bit faster in that case. Small clip-on fans are suitable for this purpose.
• Exhaust fan should always be placed at the top of the tent so it can effectively extract the warm air rising from the lights. An intake fan is not needed in smaller tents.

Fan placement in medium-sized tents

Medium-sized grow tents with an area over 2 m² may require several circulation fans and one or two fans for exhaust and possibly intake.

• Circulation fans install similarly to the smaller tents, i.e. in a corner 20–50 cm above the tops of the plants. If you want better air movement or are growing in a medium tent, place a second circulation fan in the opposite corner. The airflow should be directed slightly above the tops of the plants toward the lights.
• Additional circulation fans can be used to move air at floor level or through the middle parts of the plants. This is especially useful if you grow many plants close together, for example with the SoG method. For these purposes you can use oscillating, floor, or clip-on fans.
• Exhaust fans as with smaller tents install at the top of the growbox. In medium-sized tents a second intake fan may also be required.

Fan placement in large tents and growrooms

Large growboxes and growrooms covering tens of square meters require a more sophisticated ventilation arrangement to ensure adequate airflow throughout all parts of the cultivation area.

• Circulation fans install in every corner of the tent or cultivation room. Make sure the fans evenly cover the upper, middle, and lower parts of the plants. For larger cultivation spaces, stand oscillating and floor fans are most suitable.
• Exhaust fans must have sufficient capacity for large tents or growrooms and multiple units for intake and exhaust may be required. To successfully control and optimize climate in large spaces growers typically use automatic climate control units.

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