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Fresh Air in cannabis grow room

Nearly all living things depend on air of good enough quality. For people, that means enough oxygen is in the air and that the air is not too polluted. For plants, and so too for cannabis, good air means sufficient carbon dioxide (CO2) and no (or not too much) pollution. Furthermore, relative humidity and temperature play large roles in plant growth.

Air circulation

Air circulation grow room

Outdoor air contains about 0.03 to 0.04% CO2. The quantity of carbon dioxide is also measured in parts per million (ppm), when 0.03% translates as 300ppm. There are differences in CO2-requirements between plants. By raising the CO2 level growth can be accelerated. But with this the law of diminishing returns applies, so creating raised CO2 levels has its limits. Raising it to about 1400 ppm (0.14%) generally delivers good results (a quicker growth). Above 1400 ppm the effect of adding CO2 tails off quickly. Even for plants, a high concentration of CO2 is poisonous - for most plants a CO2 concentration of 1800 ppm or more is fatal.

A simple method of guaranteeing the level of carbon dioxide is to ventilate the space. There needs to be enough ventilation that the plants have a constant supply of fresh CO2.


Ventilation grow roomA second and equally important reason for ventilation is the removal of heat. When the temperature gets too high, the growth of the plants is hindered. This applies not just to the temperature in the grow space, but also for the temperature of the plant itself. When the temperature of the plant is too high (we humans call it a fever), then the sap stream in the plant is reduced, which in turn leads to growth retardation.

There is no standard solution for air refreshment. The need for fresh air is to a large extent dependent on the volume of the grow space in cubic metres. In principle every 2-3 minutes the complete volume of the grow space must be refreshed. Assuming a grow space that is 3 metres long, 2 metres wide and 2 metres high (= 12 m3), that means a ventilation capacity of 30 x 12 = 360 m3 per hour is needed.


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