FANS-pushing, pulling, and neg pressure theory...

[smurfin'herb]

Ok so we all have read that pulling air with fans is more effective than pushing it (for reasons that i still dont know why). So if this is true, if you set up a 6inch intake and 6inch outtake for your room ventilation, it should have negative pressure even tho the fans ARE the same size! Since the intake is PUSHING air into the room, it is working less efficiently than the outtake, therefore creating negative pressure. I have not tested this, but this theory should work based on the information at hand. Anyone have any opinions...?

 

[hoosierdaddy]

Yes, that situation would create negative pressure in the box.
Good thing about using both an intake and exhaust fan, is if one throws craps, you still have the other providing air flow.

 

[Whatever]

I have not tested this...Anyone have any opinions...?

I saw in another thread you have purchased 10's of 1000's of $'s in equipment from plantlightinghydroponics.com so why not spend a few measly bucks for a halfway decent anemometer and do some basic testing? I have yet to see 1 person do air flow testing in a grow room setup. You'd be doing a great service to the community IMO by performing some simple tests and stop any guessing or opinions and get some facts and put any bullshit to rest.

 

[FreezerBoy]

Leaving the intake fan out would also create negative pressure. Lower cost, less work, less money to buy, less money to run, less to maintain and less noise.

 

[smurfin'herb]

Leaving the intake fan out would also create negative pressure. Lower cost, less work, less money to buy, less money to run, less to maintain and less noise.

Hello freezerboy, After reading this post you are about to read i realize it comes off as kind of snobby, but i jus want you to know a head of time that im not trying to start any arguments or anything, Im just simply making statements that i believe are true. So dont be mad

leaving the intake fan out, would increase succeptibility to spores,pathogens,predators, due to the fact that you need a reasonable amount of cfm's to run any halfway decent filtration equipment on the intake, and without a fan, you simply cant run one. If you trust panty hose and such, thats cool, i simply choose a real filter.

I agree it would benefit as far as what you stated seperatley as low cost/ less money to buy (pretty much the same thing) lol. But as far as less money to run, less to maintain, and less noise. Let me ask you this, how hard is it really to maintain a fan? also, dont you think the profit you are making is overwhelmingly excessive enough to not have worry bout the few dollars per month it costs to run a single extra fan? I can see noise being a problem for smaller scale growers, but anything bigger than a 50 square foot grow, and your gonna have something/multiple things making noise regardless of what you do. Its just a fact of life.

 

[FreezerBoy]

i simply choose a real filter.

So do I. Why throw money away?

 

[dongle69]

So do I. Why throw money away?

What filter do you use that works passively?
Everyone I can find needs powered air flow to work correctly.

 

[VaporBros]

so i HAVE to have my fan sucking in the air through the filter...not pushign it out? whats the difference?

 

[Deviant420]

Some are made to be one directional, others can go either way.

(that's what she said?)

 

[Whatever]

Passive ventilation is fine IMO for smaller spaces like cabinets, tents and closets but forget about it in a large space. I tried passive ventilation in a 4800 watt space when I stepped up from a closet and failed miserably and quickly had to add some intake fans.

 

[yamaha_1fan]

so i HAVE to have my fan sucking in the air through the filter...not pushign it out? whats the difference?

Can filters can be run either way. You simply have to move the prefilter. I would think all carbon filters can be run either way but I know a rep from Can filters said theres can be run either way.

 

[Deviant420]

+1 to yamaha, I have run both my CAN100 and CAN75 both ways before.

 

[magiccannabus]

I built my own filter using silicate litter crystals and I always have it draw through the filter first. Think about this: Filtered air = less dust/dirt/etc. to clog up the fan. Want to clear all that buildup off the filter? Easy, take it into a garage or somewhere well-ventilated and reverse the flow through it, or simply take a shop vac to the outside of it. In the long run, drawing air instead of pushing it saves your fan a lot of wear.

 

[VaporBros]

tell me if this setup would work. It would save me a lot of hassle. Recirculating the stinky air.

 

[hoosierdaddy]

That will work... for about 5 minutes, vapor.
You will keep the same air in there, as well as an increasingly hot temp.

 

[VaporBros]

bah! forgot about the freakin temps!

 

[vince514]

bah! forgot about the freakin temps!

.........huh?......... cooler temps are essential for plant growth/bud developement espcially in the last critical phase of flower formation........to much heat and your plants won't produce the same as if they were in a cooler chamber/room/closet your buds will run/foxtail like crazy.. marijuana naturally cools it self off by elongating their buds(calyxes formations) to cool themselves off..............sativa's are a good example they come from hot equitorial regions from around the world.........however there's also certain indica plants that withstand temps as high as 35degrees more like afghan's and landraces located in the hindu kush mountain range's afghanistan and pakistan and espcially the hymalayan foot hills.........

but back to the topic at hand..you should be exhausting equal or greater cfm's than the intake......imho.......peace........

 

[Albert Hofmann]

hey smurfin-

If you have an intake and exhaust fan that are the same size, you will not achieve good negative pressure. And if you are looking for quality neg pressure (it is a must for odor control) then your whole prefilter for spores, pathogens, etc will be completely ineffective. Neg pressure is when your exhaust fan draws so much air out of a room that it pulls air in through every crack in the room...unless you plan on putting mini aircleaners at every crack in the floor, walls and trim your "theory" will most definately NOT pan out. If you must have an intake fan (complete waste of money) then size it 2 - 4 times smaller than the exhaust. You are worrying about the wrong things (pathogens, spores, etc), once you have done this for awhile you will understand.


albert

 

[hoosierdaddy]

Albert, for his theory to not work out, we have to assume that what you are saying is true. And your whole premise is that he will not be creating negative pressure.
I respect your take on things, but I respectfully disagree with your take.

I assure you that he is creating negative pressure by having two identical fans at intake and exhaust. Maybe you know of some force of nature or physics law that you can point to that backs up what you are saying, and if so don't hesitate to teach me. But the references I have say that you are wrong.

What he is doing is essentially the same as stacking both fans on top of another at the exhaust. The CFM didn't increase by adding the additional fan, but the pressure rating DID indeed increase. Which means he will have far greater negative pressure in the box than with just the single fan. By moving it to the intake port, you have essentially changed nothing in terms of the pressure and CFM in the box.

And sizing the intake down by 2-4 times is simply bad advise.

Some would say the key to having negative pressure is having a slight bit more air leaving than entering...but wait...that cannot happen. Trust me, it simply cannot happen. I can reference that too if needed.

The only problem we can create, is to push more air into the box than the exhaust fan can take out. Then, and only then, will air find other outlets, such as small cracks.
In the OP's situation, the friction that is created at the entrance makes it so that there is just ever so slightly less air available than the exit fan can push out, so negative pressure is created in the box. Take that to the bank.

 

[Albert Hofmann]

Albert, for his theory to not work out, we have to assume that what you are saying is true. And your whole premise is that he will not be creating negative pressure.
I respect your take on things, but I respectfully disagree with your take.

I assure you that he is creating negative pressure by having two identical fans at intake and exhaust. Maybe you know of some force of nature or physics law that you can point to that backs up what you are saying, and if so don't hesitate to teach me. But the references I have say that you are wrong.

What he is doing is essentially the same as stacking both fans on top of another at the exhaust. The CFM didn't increase by adding the additional fan, but the pressure rating DID indeed increase. Which means he will have far greater negative pressure in the box than with just the single fan. By moving it to the intake port, you have essentially changed nothing in terms of the pressure and CFM in the box.

And sizing the intake down by 2-4 times is simply bad advise.

Some would say the key to having negative pressure is having a slight bit more air leaving than entering...but wait...that cannot happen. Trust me, it simply cannot happen. I can reference that too if needed.

The only problem we can create, is to push more air into the box than the exhaust fan can take out. Then, and only then, will air find other outlets, such as small cracks.
In the OP's situation, the friction that is created at the entrance makes it so that there is just ever so slightly less air available than the exit fan can push out, so negative pressure is created in the box. Take that to the bank.

I appreciate your respectful response, however, your theories are also incorrect. My statement was based on several years grow experience and even more HVAC experience. I stand 100% by my first post.


albert