Plants inhale carbon dioxide and exhale oxygen. They need a constant supply of fresh air inside the tent to keep them healthy. I use lightweight, plastic, variable speed fans. They can be attached to the vent holes in the tent with clips. I will use one at the base of the tent for input and use one in the ceiling for exhaust. They are very noisy at full speed but these 6 inch fans do a good job of recycling the air at half speed. The speed of each fan can be adjusted to equalize the pressure in the tent.
Once the air is moved into the tent it needs to be circulated so oxygen does not get trapped under leaves. I use small oscillating fans that gently blow air over the plants, helping to build stronger stems.
I recently replaced a dead fan with a new Spider Farmer one. Hopefully it will last longer, it does have a very smooth oscillating movement.
To keep track of temperature and humidity I use a couple gauges which measure both inside and outside temperature. I cut a hole in the top of each tent and ran the outside sensor wire down into the tent. This lets me check the temperature at various levels inside the tent and compare the temperature inside the tent to the room temperature.
A portable AC unit cools the room in the summer. I keep the door closed and point the unit at the two tents. The lower vent fans do a good job of pulling in the cool air. In the winter I use an efficient ceramic heater.
Growing medical cannabis 