Ventilation in Large Grow Room

Hi, thanks for all the useful information on this site. I am a first time grower in the final stages of building a 13 x 11 x 5.5 foot grow room in the crawl space under my house. I’m have two questions:

  1. What schedule should the vent fan run on? Is it always on or periodically throughout the day? Can’t find any info on this.
  2. Not sure if I need intake ducts or if the cracks around the door ect… will provide enough intake?

Thanks again for any input from the experienced growers here.

My setup is a 4 by 4 by 8 tent. I have a fan at the top sucking air out, one at the bottom bringing temperature controlled air in. (That’s a fancy way of saying the intake is connected to a hose that I can put closer to the ceiling for more heat, or closer to the floor/AC for more cool.)

My fans are on 24/7 no matter what stage I’m at.

I also have a homemade co2 generator on the floor of the tent, right in front of the intake fan airflow.

When I started this latest adventure, I was planning on using my in ground storm shelter to grow in, but I couldn’t control the temperature.

Not sure your climate, so I don’t know if you need AC down there or even Heat.

Good luck. I’ll bet we’d love pictures.

Smell/Odor control will also likely be a concern.

Various methods to make the area nearly air tight will help and as OldGoat mentioned – running the exhaust constantly, this can create a very mild negative pressure in the room so no smell will get out through any small leaks, as they will only let air in from outside if the room is at a slight negative pressure compared to outdoors. A controlled main intake will likely be needed as well, and of course the outtake or exhaust fan will need to push that air through a carbon air filter and/or other air cleaning/deodorizing technology before it gets to the outside where you don’t want any smell remaining.

msitter says:

Thanks for the input. What kind of filtration do you have on the intake?
Also, do you have a fan blowing air in or just the vents?

Only filter I use is on the output fan. Just a 6 inch carbon filter I got from

I have a small, oscillating fan that runs constantly as well as the intake and output fans.