Positive Pressure vs. Negative Pressure

[Cerb]

I've read over and over that one should make sure their cab has a negative pressure once their fans are running. However, I've not once found a reason as to why this should be. My cab is wired with a 6" vortex intake, mainly to cool my CFL's, and a passive outtake of a much smaller diameter. The pressure inside is positive to the max, yet it doesn't seem to affect plant growth.

Why does everyone push for negative pressure?

 

[FreezerBoy]

It's not about growth but effective use of the fan and the controlling of odors. Use the fan on the exhaust with two 6" passive intakes and you'll greatly reduce stress on your fan and probably run quieter too.

By running positive pressure, odors will be forced out of seams and doors and any other crack it can find. Negative pressure will limit escaping odors to the exhaust which can be scrubbed before or after it leaves the cab.

If you can swing it, it's better to pull than to push. If you can't pull, pushing will certainly do.

 

[Chomas]

yep that sums it up perfectly

 

[CDM]

Yep.. what freezerboy said

 

[=klik=]

Peformance of vortex depends of pressure, there it works. If it suck air from growbox it will make less cfm (cube feet per minute), because less pressure on inlet. BUT if we calculate difference between two cases, we'll se what it will be so small.

 

[Cerb]

Thanks for your help guys. I'm planning a new cab build soon and this was the only thing bothering me. I haven't had any problems with odor control, but maybe I just got lucky when I was sealing my cab. The next will definitely be negatively pressurized.

 

[Whatever]

Thanks for your help guys. I'm planning a new cab build soon and this was the only thing bothering me. I haven't had any problems with odor control, but maybe I just got lucky when I was sealing my cab. The next will definitely be negatively pressurized.

Just make that intake an exhaust fan and you've got negative pressure. Passive intakes need to be like 10x the area of the diameter of the fan to get to the point where negative pressure is negligible but partly depends on which model fan, like an Elicent 6" vs a Vortex 6", due to cfm differences.

If you've got air flowing through a space you've got odor coming out the exhaust unless you're using a carbon scrubber...or growing a strain that produces no odor.

 

[Cerb]

I've got a scrubber after the exhaust on my current cab, so that's why odor hasn't been a problem.