A good ventilation setup in your growing room is very important.

Plants breathe and get rid of various unnecessary elements through foliage. When proper ventilation is not provided, the pores of the leaves get clogged, leading to the plant’s weakening and progressive death. If there is a sufficient air movement, the leaves can breathe and the plant will grow happily.

You would be amazed by the amount of new growers I met neglecting this aspect; when primarily investing a fair amount of money in their first growing equipment, unaware beginners often see it as a secondary priority, and although it is possible to grow healthy plants in poorly ventilated grow tent, the use of indoor grow fans ensures a larger and healthier development leading to a better yield.


Introduction to grow room fans

There are various types of fans you may use to maintain your plants in good conditions:

  • The exhaust fan, or extractor, is the central piece of a basic setup. It takes the air out of your grow box, renewing it and helping to maintain a bearable temperature for the plants.
  • An intake fan can be added in some cases, to increase air circulation.
  • A simple fan will always be needed to move the air around leaves and buds.

You may use only an indoor grow extractor fan and a simple fan, they create climatic conditions good enough for most of small to medium sized projects. However, an intake fan for grow tent might be needed in larger areas or in case your lamps create a high heat output.
Let’s take a closer look at these three fans.

Grow room exhaust fans, intake fans and simple fans

The exhaust fan: 

  • By sucking the air from the inside, this fan provides the basic air-renewal. It can be used alone, one side drawing in the fouled air and the other one exhausting it outside. The air intake is then passive, the depression created being sufficient enough to create a vacuum effect leading fresh air in your grow box through the intake vent left open.
  • One great advantage of air exhaustion is it also allows to cool downthe heat-loaded atmosphere induced by the lamps, especially if you use HID lights (MH or HPS) which are known to greatly increase the temperature when lit-up, and many growers use it to regulate climatic conditions when summer heat related problems show up.
  • It also helps to control humidity in your grow space. If a greater level is needed for seedlings and clones, to much humidity can lead to nasty fungi development in your buds and it should be regulated carefully during blooming stages.
  • There are different points of views when it comes to the amount of ventilation you should provide. Some like to leave the fans on all the time, others prefer to use them only once every hour using a dedicated exhaust fan timer.


There are 3 main types of fans used in grow spaces:

  • Axial Flow: they are the less powerful ones, might be used for tiny areas or in larger projects using low heat output lamps like LED or fluorescent.
  • Centrifugal Flow: those are the best ones. You can find Squirrel Cages or Vortex style models, both are powerful and will last long even when used 24/7. A major inconvenience linked to their use is the loud noise they produce, which increases accordingly to their power and the duct’s length.They are the only type you can use if you need a carbon filter for grow tent.
  • Mix Flow: these are powerful in-duct (inline) mounted fans. They are quieter than the previous ones and can be used with success in small to medium sized projects, especially if your lamps don’t increase the temperature much (LED, CFL, fluorescent tubes). However, they won’t last as long as the centrifugal types and cannot be used along with carbon filters for grow rooms.


Temperature control Equipment:

  • A Cooltube is a reflector equipped with a glass tube surrounding the bulb and connected to the extractor through an air duct. It allows the exhausted air to pass around the bulb and cool it on its way out.
  • Air cooled hoods are pretty similar to cooltubes but instead of surrounding the bulb only, the glass covers the entire surface of the reflector. They are more expensive and considered as more efficient.

Noise Reduction equipment:

Main problem of all these devices is the noise, it can be loud, very loud. If your setup is located in your house and the noise is annoying or if it’s anywhere else and you just don’t want anyone to notice that never-stopping sound you might consider those items:

  • A noise reduction box, is a simple insulated wooden box in which you place your extractor.
  • A muffler is a device you place as a part of your ducts.
  • Speed controllers for fans are used to reduce the speed and thus the noise created by the device.
  • Noise-insulated ducts.

Match your needs:

Exhaust fans have a CFM (cubic feet per minute) rating. It’s important to get a fan with the correct CFM rating for your size’s space and take into consideration the lamp’s heat output.


Here are some examples:

Room Size Minimum CFM recommended
2 x 2 x 5.25 ft 157
3 x 3 x 5.3 ft 166
5 x 5 x 6.6 ft 355 (2 lamps)
8 x 8 x 6.6 591 (3 lamps)


The intake fan:

An intake fan for grow tent become necessary when running 2 / 3 lamps or more, and using a big fat extractor to cool the place down. If too much air is being taken out without a fan bringing air in,  fresh air will go straight to the carbon filter, missing the plants on its way up. The intake fan should always be somewhat smaller than the exhaust one so the room is always under some suction.

You can use mix or axial flow models for that purpose, or centrifugal ones in really large tents.


The simple fan:

Air circulation is just as important as air replacement and should be provided at all times, especially during the budding phase. All the plants should be moving in a breeze every few seconds. Good conditions can be obtained with large ground fans or smaller oscillating fans.

However, they should never point directly at the plants, but rather on a tent’s side or above plant tops.

These fans can be pretty noisy as well despite their size, especially clip fans attached directly to your tent’s structure and creating strong vibrations.


An air-circulation fan:

  •  strengthens the plant stems, making them ready to bear heavy flower tops
  • helps control fungus and pest infestations
  • prevents the creation of hot or cold air pockets