Airflow Exchange
Expert Articles Expert Knowledge Centre
9th April 2015
Written by Gareth
Beginners Knowledge

If you have a grow room the importance of airflow cannot be overstated. Ventilation is the single biggest factor that helps to consistently produce high quality results.

There are three main roles of airflow are:

  1. The first role of airflow is to keep a constant supply of oxygen and carbon dioxide to the plant. Photosynthesis and respiration can be badly affected if these are not getting supplied in sufficient quantities. In the atmosphere, the air contains about 21% oxygen and 0.03% carbon dioxide. Not surprisingly this statistic makes carbon dioxide one of the biggest limiting factors for plant growth. If there is airflow around the plant then its supply of carbon dioxide can be maintained, if there isn't any airflow then the supply of carbon dioxide will effect the plant growth negatively.
  2. Second, airflow regulates the air temperature around the plant. The sun heats the surface of the earth, and in turn the surface heats the air closest to it. As this heats up, it rises and gets replaced by colder air further up in the atmosphere. This is convection. In a grow room, the volume of the air is limited because of its height so temperatures will rise a lot faster when the lights are on. This is called enclosed convection.
  3. Thirdly, airflow helps to control the water content in the air around the plant. Water vapour is produced by a plant during its growth and an air exchange between the plant and air occurs, the rate of which is determined by the pressure of water vapour inside the plant and that outside. This is called the Vapour Pressure Difference ( VPD ). The increase in relative humidity ( RH ) makes the VPD decrease. This makes the risk of disease increase. Airflow can remove this excess humidity. Of course, if there is too much airflow around the plant this can have a damaging effect also, as too much transpiration due to a high VPD will increase the risk of disease.

With these three considerations in mind it is recommended to:

- Invest in an extractor fan system.

This needs to be large enough to exchange the total volume of air in the room every few minutes e.g., for a grow tent 1m by 1m by 2m, the total volume of air = 2m3. So if you decide to change the air every 2 minutes, the hourly capacity of the extractor is 2 x ( 60/2 ) which is 60m3/hr. Please note, this figure only applies to extraction of air. In order to remove heat ( when using HPS grow light systems ) you may need to more than this figure.

Plan the route of your air extraction when you are building your grow room. Hot air rises so place the extractor at the top of the room. Air intake on the other hand should be nearer the floor. Don't forget to consider odour control as well - you don't want smells going out and upsetting the neighbours! Carbon filters fit onto the exhaust fan and filter out the smell.


- Create movement of air by oscillating fans.

Circulate the air inside the grow room with oscillating fans. Remember though, athough if positioned correctly they will help to manage hot spots, they will not create enough air movement to cool a room. They also serve a useful function of simulating fresh breezes and stimulate stronger stem growth. A wall mounted fan is great: one will be sufficient for a smaller grow room, but larger areas you will need two or more.


- Consider CO2

Extra C02 into a grow room will increase the yield of your crop. This is because whilst the levels of C02 in the air are on average 390 PPM (parts per million), many plants can use up to 1500-2000 PPM. This means that if yuo can increase your Co2 levels to closer to 1500ppm you will get much faster growth rates in both grow and flower stages, traditionally you would need to stop your extraction otherwise you will just be seeing the Co2 go out the extraction before it has the chance to be used. Now with new technology and use of Co2 bags there is another way.When using C02 your plants can handle higher room temperatures this can be a great advantage especially in summer. 


- Dehumidifiers and Rehumidifiers.

This will not only protect your plants from diseases arising from an atmosphere with too much moisture, But if your grow area isn't humid enough then your plants can really start to sturggle.

Ideal relative humidity levels are:

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