In all cases, the airflow capacity of the intractor must always be lower than the extractor capacity, specially when using carbon filters (thanks to the pressure all the odorous air passes through the filter). Generally, a simple inline fan will work perfectly as intractor.
There are several rules to calculate the power of the extractor in relation to the available space, but none of them takes into account all the different factors: light output used, volume of the growing space and outdoor temperature.
Using cooltubes in indoor growing tents
Cooltubes reduce the heat generated by the bulbs
Properly ventilated marijuana plants
Which extractor fan do I need for my cannabis growing space?
Never stop the air extraction system completely for some hours, since plants always need a minimum air renewal to ensure a correct respiration.
Cool tubes and cool hoods are used to guard plants from the excess heat generated by lights.
The intake fan should be always less powerful than the exhaust fan, so that, instead of the negative, you don’t get the positive pressure and the tent doesn’t get filled like a balloon, sending weed odors everywhere.
If you browse through cannabis forums, you may come across numbers like every 3-5 minutes. It could be enough, especially with weaker lights, but cheap ventilation may lead to smaller yields. So for our grow room ventilation calculator, we’ll use a more serious approach.
Oscillating fans are used inside the tent and create an air movement above the canopy level. This allows to cool down the plant tops which are the closest to the lights and suffer the most from heat.
A grow tent ventilation setup could be a most basic contraption or a very sophisticated system. It all depends on the scale of your grow-op. In any case, setting up ventilation systems for grow rooms is extremely easy if you use a few formulas and numbers that we have provided in this article.
A passive ventilation system makes use of the fact that the hot air always rises. So you only need one vent in the bottom part of your grow space and another — in the upper part. When the air gets heated by the lights, it goes out the tent through the upper hole. This creates the negative pressure, and the cool air from outside enters the tent through the bottom hole.
Example: Your grow tent ventilation kit should provide 300 CFM. You’re looking at a 680 m/h3 grow tent extractor fan. Is it powerful enough? Multiply 300 by 1.699. You get 509.7 m 3 /h. So 680 m/h3 is more than enough.
Hot and humid environments also attract various pests. Spider mites, for example, thrive and multiply in great numbers when the air is hot, humid, and stale. If you don’t want to lose your whole crop, set up a good ventilation system.
If you have a small grow box with rigid walls, rather than a grow tent, you can install a wall fan. They are also called bath fans or bathroom fans. This is a good option for those who want to buy their cheap ventilation kit locally and don’t have a hydro shop nearby.
Under this scheme, the intractor fan – which gets fresh air from the outside and directs it inside the growing space – should be placed in the lower part of the grow room. In the rare case of needing to raise the temperature of the room, even with the lights on, we should do the contrary, placing the extractor fan in the lower part of the room and the intractor fan hanging above the reflectors (which of course won’t be air cooled).
We must not forget the importance of humidity when growing cannabis indoors. When we have a small space full of plants, humidity levels rise notably, especially when plants are flowering. Our ventilation system renews the air of our grow room, keeping humidity levels at optimal values. During the growth stage , the humidity level should be around 70%, 50% during bloom to avoid mold issues. If necessary, growers also use humidifiers/dehumidifiers to raise or lower these values and provide their favourite cannabis varieties with the perfect environment.
Ventilation and temperature in indoor grow rooms
A commonly used formula to know the necessary airflow capacity (m3/h) of our extractor fan is top calculate the total volume of our grow room (m3) and remember that our extractor should renovate all the air of our room in less than 5 minutes. Of course, and in regard with temperature, it is not the same using CFL’s or LED panels than HPS lamps. The temperature of our grow room also depends on both the airlfow capacity of our intractor fan and the place where the air comes from: it is quite different having the air intake inside the house than in a shady and fresh corner of our backyard. Thus, before purchasing our extractor fan, we must take into account both the total volume of our grow room and the lighting system used.
Climate control systems for cannabis grow rooms
This is why, normally, air extraction fans are used in all indoor grow rooms, to which growers connect carbon filters to remove the odour from the plants while also removing heat and humidity. For improved performance, growers also use intractor fans (always of lesser airflow capacity than the extractor fans, so negative pressure is created and odours don’t escape the growing space through holes or zippers) which are constantly supplying the grow room with fresh air from the outside. Finally, using fans inside the growing space is also recommendable, since they produce a constant airflow that helps avoiding heat/air pockets.