G
gazcat
My exhaust is twice the CFM as my intake, what are the benefits? What are the disadvantages as opposed to the other way around. Thanks!
W
Whatever
You most likely have extreme negative pressure and are putting unnecessary strain on the exhaust fan. Instead of going with a passive intake I'd recommend using a speed controller to slow down your exhaust fan a bit. An active, as opposed to passive, intake is always better. You want negative pressure for odor control but you only need a little bit of negative pressure...I mean like your exhaust fan trying to pull out just a bit more than your intake fan can feed in. That's all you need. Passive intakes are OK for very small grow spaces IMO.gazcat said:
To check for negative pressure just use a lit stick of incense around the door/opening(s) to the grow space when closed...if the smoke goes in your golden.
Your exhaust is not twice the CFM as your intake. You can't exhaust more air than you bring in. Exhaust can be double the size of the intake but, it's an inefficent way to do things. Either two exhaust fans that get back to the fact that you can't exhaust more than you intake or, with one intake fan, you run the risk of positive pressure.
One powered exhaust with dual passive intakes allows you to pull air rather than push while retaining negative pressure.
One powered exhaust with dual passive intakes allows you to pull air rather than push while retaining negative pressure.
W
Whatever
If you have a 400cfm fan on the exhaust side and a 200cfm fan on the intake side what is that? I think that's what he's talking about. Also it does not matter how many exhaust or intake fans you have just the total volume trying to be exhausted and the total volume that can actively be fed to the space.FreezerBoy said:
In any passive intake setup I've seen negative pressure has never been a problem and always present...unless someone builds a very leaky room I guess.
That's overstressing your fans and increasing noise while restricting exhaust to the amount of air coming in.Whatever said:
Which is why it's a benefit.Whatever said:
W
Whatever
Most passive intake setups I've seen are undersized restricting airflow too much.FreezerBoy said:
JohnnyToke
Member
as Freezerboy stated, your exhaust fan can only exhaust the amount of air allowed in thru the intake. want to increase air flow & exhaust more air? make the intake larger or add additional passive intakes so that a larger volume of air can pass through. I believe a passive intake allows a centrifugal (vortex) exhaust fan to be more effective than running an intake fan at half the cfm's of the exhaust fan.
just my .02 cents through trial & error on my personal grow closet.
JT
just my .02 cents through trial & error on my personal grow closet.
JT
That's called bad carpentry.Whatever said:
2X Exhaust=IntakeChaghatai said:
G
gazcat
Ok so would it be best to go 2X intake = exhaust?
I could get a 8" 500cfm can fan for an intake and a 6" 250cfm for exhaust
I could get a 8" 500cfm can fan for an intake and a 6" 250cfm for exhaust
You got it backwards. 1/2 intake=exhaust. Example 8" intake=4" exhaust.gazcat said:
Use the 500 on the exhaust, cut two 8" intakes and leave them open. Leave the 250 at the store and use the money on beans. Forced intake larger than the exhaust can handle makes the exhaust a bottleneck and creates positive pressure. Positive pressure bad.
Forced exhaust, the bottleneck is on intake. That's what gives you negative pressure.
G
gazcat
No I am saying the most efficient way to vent is with a active intake? rather than passive?
im simply asking if a 500cfm intake and a 250cfm exhaust would be a good thing
im simply asking if a 500cfm intake and a 250cfm exhaust would be a good thing
JohnnyToke
Member
gazcat said:
bro, the most efficient way for exhausting a room that you want negative pressure to control smell is a fan on your exhaust pulling air out of the grow thru passive intakes (no fan). you do not want a fan on the intake.
blowing air into the intake causes positive pressure and can lead to smell leaks among other things. you dont want that.
as most of us have all suggested, make your passive intake 2 times larger that the exhaust hole where your fan is. if you need more airflow, make it 3-4 times as large.
I assure you, there will be plenty of air flowing thru your grow.
make the intakes down low and the exhaust up high.
good luck.
JT
G
gazcat
My grow is in my closet and smell really isnt a big deal... whast the best way?
W
Whatever
JohnnyToke said:
That first statement is only true basically if the cfm's of your intake fan(s) exceed the cfm's of your exhaust fan(s)...then you have positive pressure...really simple.
As for the second statement basically make sure your intake is on the opposite side of the room/space as your exhaust so the air flows across the grow space.
For a small grow like a closet one exhaust without an intake fan, relying on a passive intake, is fine. How many watts are you planning on running and in what size space? So are you saying if odor leaks from the closet into the living space no problem?
JohnnyToke
Member
I grow in a closet as well. 7' L x 5' W x 8' T. I have tried just about every possible setup for exhausting, intakes with fans, intakes without etc etc. to keep fresh air moving thru, temps down and smell under control.
you say smell wont be an issue now because your growing in your closet but wait til you are 5 weeks into flowering. any smell seepage will smell up your entire house, apt etc. you will see....lol
most of us have told you what works best and most efficient.
at this point, you just need to try it with an intake fan, then without and see for yourself.
my .02 is pumping air in with a fan and pulling air out with another cause the fans to stress. A central a/c unit on a home or apt has a passive intake for a reason, it is the most efficient way to create airflow.
regards,
JT
you say smell wont be an issue now because your growing in your closet but wait til you are 5 weeks into flowering. any smell seepage will smell up your entire house, apt etc. you will see....lol
most of us have told you what works best and most efficient.
at this point, you just need to try it with an intake fan, then without and see for yourself.
my .02 is pumping air in with a fan and pulling air out with another cause the fans to stress. A central a/c unit on a home or apt has a passive intake for a reason, it is the most efficient way to create airflow.
regards,
JT
Farmer John has 19 cows. All have balloons attached to their butts. After a fine meal of bean and hay burrittos and several kegs of Shlitz Malt Liquor, the cows begin to fart. The balloons swell and eventually burst, permeating the barn with the foul smell of concentrated methane. Why? Positive pressure. Gas enters the enclosure faster than it can exit causing the balloon to explode. Explosions bad. Positive pressure=explosions=bad. Positive pressure bad.gazcat said:
No your cab won't explode, but your fan noise will climb, fan life will drop, electrical payments will rise, your house will stink, your neighbors will all know what your doing as will any policeman who strolls by your door.
The best way to get arrested is to put up a neon sign and scream from your front yard that you're growing pot while blowing smoke into the face of local gendarmes and passing out samples and clones. But pumping positive pressure into your cab is a close second. Make sure your affairs are in order and your lawyer well paid. Then kiss your freedom goodbye. Have fun in jail.
Quazi
Member
Damn, and I thought this was just a friendly conversation about ventilation concerns. Thanks for the info about the negative/positive pressure though.FreezerBoy said:The best way to get arrested is to put up a neon sign and scream from your front yard that you're growing pot while blowing smoke into the face of local gendarmes and passing out samples and clones. But pumping positive pressure into your cab is a close second. Make sure your affairs are in order and your lawyer well paid. Then kiss your freedom goodbye. Have fun in jail.
Now I know. And knowing is half the battle.
W
Whatever
An active system only causes UNDUE stress if not balanced properly. Having negative pressure, even minor, with a passive intake is putting stress on the fan cause it's trying to exhaust more air than it can take in. Too small a passive intake and UNDUE stress.JohnnyToke said:
A central home unit is efficient because it is pulling in air from the same space it is exhausting into...the fan is basically pulling from and exhausting into a closed box...no pressure differential. It also has a passive intake because it is less expensive and also in this case the passive intake is sized properly by professional engineers.
Positive/negative pressure regulation is soooooo simple in an active system.
