DIY DIY grow space-heat needed!

[Tom Bombadil]

Ive been able to exchange air every 30-45 minutes in a semi-sealed 4x4 tent grow with no co2 supplement and grew massive buds with no ill effects..

 

[Bruce Campbell]

The suggestion at Royal Queen Seeds is to fully replace air in the growdrobe once per minute.

To this point - I've usually seen the general rule of thumb of 2-3 turnovers per minute.

So, for a 4' x 4' x 8' = 128 ft^3 grow tent, then you "need" a 128 x 3 = 384 cfm fan.

[Edit: That rule of thumb is usually from someone trying to sell you a fan - not what you need for CO2. Estimate airflow from your own temp/humidity needs instead.]

But, as indicated above, your flows needed for temperature and/or humidity control are typically gonna be higher than those needed for CO2 consumption, and temp/humidity ventilation needs will vary based on your specific situations and setup.

 

[Tom Bombadil]

To this point - I've usually seen the general rule of thumb of 2-3 turnovers per minute.

So, for a 4' x 4' x 8' = 128 ft^3 grow tent, then you "need" a 128 x 3 = 384 cfm fan.

But, as indicated above, your flows needed for temperature and/or humidity control are typically gonna be higher than those needed for CO2 consumption, and temp/humidity ventilation needs will vary based on your specific situations and setup.

Air exchange is dependent on humidity and temp more than anything else. 2-3 x per minute is overkill. Air movement is more important imo... plants use a lot less co2 than people think. a tent full of air has enough co2 to last for quite a while, unless maybe youre tent is way over crowded.

 

[Rapha El]

humidity is the real burden when it comes to slow air exchange.. if you do it entirely temp like i suggested you're gonna raise your rh quite a bit. and that quite consistently as you're always just diffusing new cold air into the tent. Ideally you'd have a low basic exchange and then bursts based on high temps.

the high cfm suggestions are likely so people can still grow some nice bud even without a second fan just for turning over the air inside the tent. the first few years all I had was my extraction fan to provide any sort of air movement and it was enough.. only recently have I added a second, in-tent, fan and seen the benefits of it. and to be quite honest I was surprised how much of a difference it actually makes.
I got an oscillating fan that blows 15 minutes every hour, in the general direction of everything and my seedlings grew way sturdier. None of them fell over and required propping up. And I think they also grew faster but haven't gotten anything for a 1:1 comparison so take that with a grain of salt.