Air flow and CFM rates

[Jin Terra]

Ok so when I've grown before I didn't have to worry about smell. I usually had a fan for circulation and another to pull out hot air from the lights. Easy.

Now I have those concerns and have some questions.

My grow area is roughly 64cf or 3x3x6. I've been shopping for inline fans, carbon scrubbers and trying to figure out to keep my airflow balanced. If I buy a inline fan that is capable of 203cfm attached to a carbon scrubber that allows 52% intake of airflow does that mean assuming I'm running that fan @ 100% that I'll move 101cfm? I know I don't want to move that much air out in a small space that fast but I'm just trying to figure out the math behind it.

Also I believe I should get a second fan (can fan) or whatever to bring in the same amount of air the scrubber is putting out or is there some kind of ratio of air in/out I should use as a guideline?

Any advice is appreciated.

 

[TurboBucket]

Variable speed control will help adjust how much air your fan(s) move. How much air you need is dependent on several factors your ambient temperature and grow space heat sources (lights, pumps, fans etc..)being the biggest two. If your not exhausting tons of air a passive intake is fine and reduces costs.

 

[AnimaSola]

Your intake should always be less cfm than your exhaust to create negative pressure and keep the smell in. If you have two of the same size fans you can have a positive pressure issue and leak odor from every crack.

Weather you need an intake or not depends on the size of your room and fan. If your exhaust fan can exchange the air in your room every few minutes you don't need an intake.

 

[Jin Terra]

Thank you Turbo and Luweedgi.

Just to clarify, what you guys are saying I want to make sure that my intake is always less than my output. Considering that I'll be using a tent this is important. I'll be using a variable speed fan with a scrubber for the output and as long as the fan is set at a speed that is equal to or greater than what the intake is then I should be ok in terms of smell and air quality.
If I go passive on the intake (meaning no fan pushing air in) then a low setting on the output should suffice in air quality and odor control correct?

My space is a tent that's 3x3x6 or 54cf. So setting the fan to output let's say 26cfm is enough to created that negative environment with needing a second fan for input. Or should I have a fan for input anyway to be safe?

 

[TurboBucket]

Your on the right track yup. You suggest 26cfm. The amount of air needed is very variable across grows. It depends on how much heat you have inside your tent and how cool the air your bringing inside it is. Big HPS with hydro pumps and circ fans would use more exhaust air than a couple LEDs with dirt pots.
You can create negative pressure with very little airflow just needs to be a well sealed chamber (exhaust > infiltration).

 

[Dr Fish]

I bought one of these to check air flow instead of guessing at the air flow.... GM816 Digital Handheld Anemomete, Pocket Digital Anemometer with LCD Display for Measuring Wind Speed, Temperature and Wind Chill (Yellow)

Or for a little more money this one,
Tacklife Digital Anemometer Handheld, DA02 Classic Wind Speed Meter Measuring Temperature Speed and Wind Chill with LCD Display, MAX/MIN Mode and Hold Data Function

 

[Jin Terra]

Great tool! Thank you Dr. Fish