Where and how to correctly place fans in a grow tent or grow room

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

When growing plants indoors, we use two basic types of fans, each for different purposes. Extract fans remove “stale” air from the growing space. Fresh air can be supplied passively, or a second fan can be used for this purpose, which is especially useful in larger grow rooms. Constant air exchange helps maintain a stable temperature and humidity in the growing space. A consistently optimal climate is important both for plant photosynthesis and as prevention against mould and the spread of pests.

Circulation fans placed inside the growing space are designed to imitate the natural wind that affects plants outdoors and stimulates them to form strong stems. Constant air movement also makes life more difficult for pests and discourages them from settling on plants. Correctly positioned circulation fans help prevent pockets of hot or cold air from forming, for example under lights or in the corners of the grow room.

Types of fans for indoor growing

• Clip-on circulation fans are the most commonly used type. They can be easily attached to the tent poles and are best suited to small or medium-sized grow boxes.
• Oscillating pedestal fans are suitable for moving air in medium-sized or large tents and grow rooms. They take up slightly more space than the clip-on version. They are usually larger and, thanks to oscillation, cover more of the growing area.
• Floor fans stand out for their high output and are most often used in large grow rooms, where they move air between the aisles with plants. They can also be used in large tents. Be careful with the strong air stream, which may damage plants.
• Extract fans of various types are an essential part of every indoor grow room. Older types with an AC motor are noisier and consume more energy than newer models driven by an EC motor. More modern versions of extract fans are easier to regulate and the purchase price is slightly higher.

Fan placement in small tents

In small grow tents with roughly up to 2 m² of growing area, you will usually manage with one extract fan and one circulation fan.

• Circulation fans should be placed in the corner of the tent 20-50 cm above the tops of the plants. The air stream should reach both the upper 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 output so that the air does not dry out the plants. For this purpose, small clip-on fans with or without oscillation are sufficient.
• Additional circulation fans are usually not needed in small grow tents. If you wish, you can place one small fan at the base of the tent so that the air is directed at the lower parts of the plants. In that case, the substrate will dry out slightly faster. Small clip-on fans are suitable for this purpose in small tents.
• Extract fan always belongs in the upper part of the tent so that it can efficiently remove warm air rising from the lights. An intake fan is not necessary in smaller tents.

Fan placement in medium-sized tents

Medium-sized grow tents with an area above 2 m² may require several circulation fans and one or two fans for extraction and possibly also air intake.

• Circulation fans should be installed in a similar way as in smaller tents, that is, in the corner 20-50 cm above the tops of the plants. If you want to ensure better air movement or are growing in a medium-sized tent, place a second circulation fan in the opposite corner. The air stream should be directed slightly above the tops of the plants towards the lights.
• Additional circulation fans can be used to move air near the floor of the tent or in the middle parts of the plants. This is especially useful if you are growing many plants close together, for example with the SoG method. For this purpose, you can use oscillating, floor or clip-on fans.
• Extract fans, just like in smaller tents, should be installed in the upper part of the grow box. In medium-sized tents, a second fan for air intake may also be needed.

Fan placement in large tents and grow rooms

Large grow boxes and grow rooms with tens of square metres of area require a more sophisticated ventilation arrangement to ensure sufficient air flow in all parts of the growing space.

• Circulation fans should be installed in every corner of the tent or grow room. Make sure the fans evenly cover the upper, middle and lower parts of the plants. For larger growing spaces, oscillating pedestal and floor fans are most suitable.
• Extract fans must have sufficient output in the case of large tents or grow rooms, and several units for air intake and extraction may also be needed. For successful climate control and optimisation in large spaces, growers usually use automatic climate control units.

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