Ventilation will keep a grow room at a proper temperature range. It will also supply plants with carbon dioxide (CO2) which is necessary for photosynthesis. During a typical grow day plants will use CO2, nutrients and light in order to grow, if there is no ventilation and no fresh CO2 being introduced into the grow room, plant growth will slow down and possibly even stop.
This is why having fresh out door air pumped into the grow room on a regular basis is very important, even with temperature at an appropriate level, ventilation needs to go on at least for a few minutes 2 or 3 times during a grow day.
During the Great White Shark grow I used a 175 CFM (Cubic feet per minute) exhaust fan, this is bigger then necessary for the 2 by 2.5 by 6 foot grow tent, but its better to have a bigger exhaust fan then otherwise, a larger exhaust fan will also take care of pot odor in the rest of the grow address. The exhaust fan was controlled using a temperature sensor that I placed at the top of the plant canopy, once temperature reached a certain predetermined level the exhaust fan would be automatically turned on and run until temperature went down to an acceptable level.
In terms of introducing fresh air (CO2) to the grow tent, I used a window fan during the winter/early spring and an air conditioner during the summer. The exhaust fan was set up to pump hot air out of the grow tent with a vent hose running to the window, the exhaust fan has a carbon filter attached to it.
- Attach a carbon filter to the exhaust fan for odor control
- Hang the carbon filter near the top of your grow tent connected with a duct-hose to the exhaust fan
- Hot air rises so it will be warmer near the top
- Use an Air Conditioner or window Fan to supply fresh outdoor air to the grow area