# blow in or suck out air??



## beeznutz (Jan 20, 2011)

i jus set up a room at my new place, it's 8x7x6.5, and getting ready to go into flowering. i want to keep it sealed and id like to know if i could just use 1 fan for circulating air. this is happening in the basement, i'm in ohio, and it is pretty cold right now so i actually have to run a heater to keep the temp right also a humidifier to get that up cause it seems to be pretty dry.
what i have in the room right now:

1x1000hps
1xCoolmist Humidifier
1xHeater

at the moment i only have 2 haze growing with 15 clones coming soon.
so, because of temp being cold i'm concerned when i switch to 12/12 [im running 24/7 right now] it'll get pretty cold so i dont need a lot of circulation but i'm thinking i should be able to jus use one fan [i have a vortex 600 running at 465cfm and a vortex 800 @700cfm] to get it done.
my question, what's the best way around it? should i have the fan ouside the room with duct running on top of the growroom and suck the air out while having one or multiple 'holes' on the bottom of the growroom which i'm thinking it'll bring in fresh air.......or......have the fan blow in fresh air with one or multiple holes on top of the growroom to exhaust the air?

thx in advance....


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## Nubby Tubbs (Jan 20, 2011)

pulling air thru an inline allows up to 4x more air flow...thats in cervantes bible. bends drastically decrease flow as well, but i have a few my hood vent.


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## Bonzi Lighthouse (Jan 20, 2011)

Suck don't blow.


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## g13hydo (Jan 20, 2011)

you should always be exauhsting more air then your have coming in

and id get fresh air in before your planned on exauhsting the stale air stale air can also lead to powdery mold

i pull air from my bedroom window which is pulled from a 6' 400cfm active air fan which cools both of my 600w hoods along with pulling fresh air in and a 8' 700cfm fan pulling air out


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## beeznutz (Jan 20, 2011)

k, cool- pull it is.....
jus having some holes on the bottom of the room should b enough then, for fresh air to b sucked in?
I'm not ready to set up the exhaust system to bring air from outside but my basement is pretty big , 35'x30 and I'm only using 8x7 for the grow room- is good enough fir now ?


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## cowasaki (Jan 20, 2011)

yeah ull be fine..put some holes in the bottom and exhaust the air out... show some pics of ur girls bro


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## FootClan (Jan 20, 2011)

beeznutz said:


> i jus set up a room at my new place, it's 8x7x6.5, and getting ready to go into flowering. i want to keep it sealed and id like to know if i could just use 1 fan for circulating air. this is happening in the basement, i'm in ohio, and it is pretty cold right now so i actually have to run a heater to keep the temp right also a humidifier to get that up cause it seems to be pretty dry.
> what i have in the room right now:
> 
> 1x1000hps
> ...


you said you want your grow to be "sealed" as in a sealed grow? that would mean you wouldnt be bringing in air from outside becuase your grow room would be sealed off and you would need C02 supplement......Are you talking about something esle when you say "sealed" or "closed loop" just wondering little confused


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## greenkrakzak (Jan 20, 2011)

just remember, if your stems get weak tho, start to blow, it will help simulate the wind blowing the plant and strengthen the stem


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## beeznutz (Jan 20, 2011)

@footclan....yeah, I meant as a room, it's sealed from the elements and the surroundings..and I'm setting up the exhaust to bring inair then exhaust out...maybe I don't have the terminology right- wouldn't that be considered sealed?

@greenkrakzar.... I will have a rotating fan inside running 24/7 

@cowasaky....yeah man, ill get some pix tonite.


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## FootClan (Jan 20, 2011)

beeznutz said:


> @footclan....yeah, I meant as a room, it's sealed from the elements and the surroundings..and I'm setting up the exhaust to bring inair then exhaust out...maybe I don't have the terminology right- wouldn't that be considered sealed?
> 
> @greenkrakzar.... I will have a rotating fan inside running 24/7
> 
> @cowasaky....yeah man, ill get some pix tonite.


as far i know it a sealed room means the same as a closed loop room....meaning the room is completly sealed off from the outside envierment......The only reason to bring in air in a sealed room would be as to cool your lights and that air wouldnt mix with the air inside the room...meaning you pull air from outside into ducting then past your light then back ouside never mixing with growiing envierment...but you are talking about bring in fresh air into your tent then exhausting it back out someplace else....thats not really sealed room becaue you have an exchange of air inside your growing envirment that came from another place....

So what you doing is just a normal grow not really sealed.......unless im missing somthing here....dosent really matter anyways just tryin to get on same page here...


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## Mr.Sativa (Jan 20, 2011)

Dude...if it's cold, you need to bring in air from the top of the room, because hot air rises. Pull air in from top, exhaust from bottom. I'd say it doesn't really matter where you put the fans, or if you use two fans for this...as long as you're doing this...you'll be fine. I'd use two fans...but that's just me...i like to overdue it a bit. You should have an oscillating fan in the grow room for plant sturdiness and basic in-room circulation, butttttt...that's kinda gonna mess up the airflow, depends on how big/powerful the OC fan is, that's why i'd use two of the same fans...for intake and for outake so you wouldn't have messed up airflow by OC fan. What i've normally seen is taking in and taking out the same amount of air, i don't know about exhausting more air than you put in, i don't know if that's possible...how would you put out more air than you're putting in? idk haha. But yea, i maybe wrong you never know, i'm actually gonna look this up!! g13hydo i'm not being an ass, id really like to know where you got this from! =)


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## beeznutz (Jan 20, 2011)

thx, that clears it.... and makes sense.
def not gonna have co2 so my final plan is to have a fan blowing outside air thru the hood then blow back out and also another fan blowing fresh air in the room then exhaust thru filter and outta chimney. but I won't get there till it gets warm out, right now I just need air circulating thru the room.
I will have to play&monitor the room but what do u guys have ON during lights off? and do u think it'll b fine using the air from the basement to circulate?


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## FootClan (Jan 20, 2011)

Mr.Sativa said:


> Dude...if it's cold, you need to bring in air from the top of the room, because hot air rises. Pull air in from top, exhaust from bottom. I'd say it doesn't really matter where you put the fans, or if you use two fans for this...as long as you're doing this...you'll be fine. I'd use two fans...but that's just me...i like to overdue it a bit. You should have an oscillating fan in the grow room for plant sturdiness and basic in-room circulation, butttttt...that's kinda gonna mess up the airflow, depends on how big/powerful the OC fan is, that's why i'd use two of the same fans...for intake and for outake so you wouldn't have messed up airflow by OC fan. What i've normally seen is taking in and taking out the same amount of air, i don't know about exhausting more air than you put in, i don't know if that's possible...how would you put out more air than you're putting in? idk haha. But yea, i maybe wrong you never know, i'm actually gonna look this up!! g13hydo i'm not being an ass, id really like to know where you got this from! =)


i really doubt a ocilating fan inside your tent is going to mess up airflow into your filter.....


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## FootClan (Jan 20, 2011)

beeznutz said:


> thx, that clears it.... and makes sense.
> def not gonna have co2 so my final plan is to have a fan blowing outside air thru the hood then blow back out and also another fan blowing fresh air in the room then exhaust thru filter and outta chimney. but I won't get there till it gets warm out, right now I just need air circulating thru the room.
> I will have to play&monitor the room but what do u guys have ON during lights off? and do u think it'll b fine using the air from the basement to circulate?


so your going to have 3 inline fans??? one fan for dedicated light and hood?, one fan for intake? and one fan for exhaust?? thats seems just unnessary really and waste of money.......why not just two fans...one dedicated for light and hood and one for exhaust that is creating negative pressure... i dont get why you want to have an intake fan blowing air inside..the exhaust fan if big enough will suck hard enough to bring in fresh air though the passive vents at the bottom elimanating the need for the intake fan....


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## Mr.Sativa (Jan 20, 2011)

ok so the suck out more than take in is good...seems like it creates a negative pressure and ensures no smell leaks out of small cracks that every setup has. Since you'll be pulling more air out than in, you'll be pulling air from the small cracks and fissures...at least this dude ( http://forum.grasscity.com/grow-room-design-setup/465217-more-exhaust-more-intake-why.html ) explained it like this. About OC fans in the tent, i think it would uneven a passive exhaust as it's circulating air inside, but whatever, it doesn't really matter, you'd still have air coming in and out. I think footclan's right, having one exhaust fan capable of ensuring the negative pressure...is all you need! If i weren't using two fans for out/intake i'd just use a fan exhaust and passive intake!


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## beeznutz (Jan 21, 2011)

footclan, thx for the input- I see what ur saying...I think I was thinking ahead, when it gets hot in the summer and by then I should have more lights in the room (I'm thinking 1x1000 in the middle and 4x200w cfl hanging in all four corners) ....
with that in mind, how would u set up the fan for the light?
suck from light out or blow in ? and would u have the hood sealed or opened?
also, is it really necesary to bring air from outside the house or would the air from the basement b fine?


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## g13hydo (Jan 21, 2011)

its hard to tell you what you should do without pictures. im not going to go on someones thread and advise them to do something thats not right. im just giving my opinion on whats worked for me as every situation is different. and i got that knowledge from years of experience.

fresh air is always better than stale air. as you will get into problems with mold and what not if your plants are too humid or vice versa. i would work on cooling you biggest light first. and always when cooling a hood you should have it sealed.blowing air to a light works better to cool it then sucking air from the light in my own opinion. also the less bends the better air flow. if your going to be using cfls you can use a oscilating fan to cool them. or a stationairy fan that just cools the cfls. cfls can be acouple inches away from the tops of plants as 1000whps would have to be atleast 18 inches to 48 inches away


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## LRGenius420 (Jan 21, 2011)

Ok If I were you... Id only get one good fan that is strong enough for that room... save money... I have a 5x5x6.5 and i only need the second to the cheapest inline fan from active air. I got a fan speedcontroller for 29 bucks, Than you need a fan that will pump air into your room from outside right, Whatever you do you want the airflow to be slightly more than what is going out of the tent, that way the tent stays slightly puffed up or full of air. if you are running co2, turn down the speed of your intake fan... turn off you exhaust and let it flow..
A tent will never be completely sealed unless you tape up the whole dame thing. 
I hope this helps a few of you out


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## LRGenius420 (Jan 21, 2011)

I forgot to mention, split the intake fan and send 1 duct thru the light and out of the tent, and the other duct into the tent


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## FootClan (Jan 21, 2011)

g13hydo said:


> its hard to tell you what you should do without pictures. im not going to go on someones thread and advise them to do something thats not right. im just giving my opinion on whats worked for me as every situation is different. and i got that knowledge from years of experience.
> 
> fresh air is always better than stale air. as you will get into problems with mold and what not if your plants are too humid or vice versa. i would work on cooling you biggest light first. and always when cooling a hood you should have it sealed.blowing air to a light works better to cool it then sucking air from the light in my own opinion. also the less bends the better air flow. if your going to be using cfls you can use a oscilating fan to cool them. or a stationairy fan that just cools the cfls. cfls can be acouple inches away from the tops of plants as 1000whps would have to be atleast 18 inches to 48 inches away


Na its better to PULL air through the hood then push it out the backside........If you are planning on using a Carbon filter with a one fan set up then you will want to PULL the air through the filter then past the hood........The filter is designed to have air pulled through it not pushed through it......


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## Stonetech (Jan 21, 2011)

Listen to footclan, the exhaust fan should be the last thing in line before leaving the grow space. Fans work best when the path in front of them is unobstructed. Passive intake is all you need, start with one that is double the size of the exhaust and adjust from there. You want slightly less air coming in than going out in order to prevent odor leaks (negative pressure).


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## legallyflying (Jan 21, 2011)

Just as an FYI, plants dont like sitting in a negative pressure environment. Ergo..in a setup with a large exhaust fan but small fresh air fan. People don't seem to grasp that it is virtually the same in terms of heating and cooling. If I were you I would put a small inlet fan down low and use passive vents up high. Very small fan and carbon filter scrubbing inside the tent. Another very small fan sucking air through the tent and hood. Seal your light up well and u don't have to worry about smell, the light is "external" to the tent.


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## Stonetech (Jan 21, 2011)

legallyflying said:


> Just as an FYI, plants dont like sitting in a negative pressure environment. Ergo..in a setup with a large exhaust fan but small fresh air fan. People don't seem to grasp that it is virtually the same in terms of heating and cooling. If I were you I would put a small inlet fan down low and use passive vents up high. Very small fan and carbon filter scrubbing inside the tent. Another very small fan sucking air through the tent and hood. Seal your light up well and u don't have to worry about smell, the light is "external" to the tent.


I've never seen or heard of anyone using your method so I can't say it wouldn't work, but, i do know that a fan is much more efficient sucking air out. Also If you suck air out through a filter you only need one fan to do it vs. your intake fan + fan for scrubbing. I also know that your right about using a smaller cfm fan for intake as this would cause too much neg pressure. However, if you made the passive intakes the right size for your exhaust there would be minimal neg pressure and you would have no odour leaking.


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## FootClan (Jan 21, 2011)

Stonetech said:


> I've never seen or heard of anyone using your method so I can't say it wouldn't work, but, i do know that a fan is much more efficient sucking air out. Also If you suck air out through a filter you only need one fan to do it vs. your intake fan + fan for scrubbing. I also know that your right about using a smaller cfm fan for intake as this would cause too much neg pressure. However, if you made the passive intakes the right size for your exhaust there would be minimal neg pressure and you would have no odour leaking.


No stonetech im with you what your saying makes more sense then what he was saying....rep for you !


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## beeznutz (Jan 22, 2011)

hey guys..... so I tried to take some pix but my iPhone is the only camera I have and for some reason they come out weird, really orange-yellow and it has these faded 'lines' accross all pix- anybody had any luck taking pix with iPhone in a growroom??

so for now I've installed the 400 something CFM fan as a blower of fresh air . ran a duct from it to the top if the growroom and it's blowing on the backwall which bounces back and hits the plants so that gives them some wiggling and from there it goes outta bottom of the front door, which is just a Mylar flap taped on the top to about half way down and just left the bottom free falling to let the air out.
Temps during lights on are totally dialed in @ about 75, that's the reading everytime I check throughout the day and when checking on the min&max reading on the temp gauge, it's between 71-79- SWEET!
it's only been a day of lights off and it did dip to about 59 so had to turn up the heater, we'll see what happens today.....

I'd like to know more about this negative pressure if somebody could point me in the right direction......


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## Stonetech (Jan 22, 2011)

So your blowing air into the top of your room? you should be sucking it out. You've got it ass backwards. You need to blow air out through the top. The intake must be near the bottom and the exhaust at the top in order to exhaust the hot air. If you do this your temps probably won't climb as much.

Negative pressure just means that your removing air from the grow faster than it is being replenished, creating a vacuum. The reason why you would do this is to ensure that all the air that is escaping the grow is being sucked through your exhaust so the rest of your house doesn't stink. If you are blowing air into your grow faster than it is escaping then its going to find other ways to escape other than your designated exhaust (filter). Any pinhole or crack in your grow is going to allow the stank to get out to where you don't want it to be. Although if you aren't venting your exhaust outside or filtering it and you want your house to stink like weed then you don't need to bother with negative pressure. 

And by the way I wouldn't take pics of your setup with lights on with your iphone, I tried once with my camera phone (not an iphone) and now the camera longer works, maybe camera phones are too weak not sure but iphones are expensive.


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## FootClan (Jan 23, 2011)

Stonetech said:


> So your blowing air into the top of your room? you should be sucking it out. You've got it ass backwards. You need to blow air out through the top. The intake must be near the bottom and the exhaust at the top in order to exhaust the hot air. If you do this your temps probably won't climb as much.
> 
> Negative pressure just means that your removing air from the grow faster than it is being replenished, creating a vacuum. The reason why you would do this is to ensure that all the air that is escaping the grow is being sucked through your exhaust so the rest of your house doesn't stink. If you are blowing air into your grow faster than it is escaping then its going to find other ways to escape other than your designated exhaust (filter). Any pinhole or crack in your grow is going to allow the stank to get out to where you don't want it to be. Although if you aren't venting your exhaust outside or filtering it and you want your house to stink like weed then you don't need to bother with negative pressure.
> 
> And by the way I wouldn't take pics of your setup with lights on with your iphone, I tried once with my camera phone (not an iphone) and now the camera longer works, maybe camera phones are too weak not sure but iphones are expensive.



i agree .......just didnt have the energy to explain it to him......He was told by someone else in here to have his intake at the top because hes sucking in cold air......i just let it go


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## resinousflowers (Jan 23, 2011)

ive had many successful grows with just a exaust fan and passive intake holes.


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## legallyflying (Jan 23, 2011)

I'm not quite sure why you guys have the belief that fans work better sucking than blowing. All pressures being equal, the flow rates for intake bad exhaust are the same by definition. What I mean is, put the fan on the table and plug it in, the amount coming into the fan is exactly the same coming out. Any resistance to flow will effect intake and exhaust the same. 

I didn't tell anyone to blow air in up top as that doesn't make any sense at all. You want to work with convection flows not against them. The advantage if the set up I described is greater climate control AND smell control. If your scrubber and ventilation are separated, you can put your exhaust fans on a thermostat and they will turn on and off as needed to maintain the desired temps. At night, when you want to keep it warm and not exhaust you can turn off the vents and run a small heater. 

If you have your filter attached to your ventilation that means you have to run the filter 24/7 thus always blowing cold air in the tent. Lastly, a filter set up as a scrubber is more effective at eliminating odors than an exhaust. As canaboids are volitile organic carbons, they will easily pass though the walls of your tent, especially in the areas that have somewhat stagnant air flow if your just exhausting. Lastly, a scrubber exhaust can be directed at the plants to increase airflow, increase gas exchange, and combat bud rot; your essentially using it in place of an oscillating fan. The hydrofarm online booster fans work great for ventilation and climate control and are only $50. 

If your going to have a passive inlet or outlet, you want it to be 3x the size of the powered inlet/outlet to ensure even exchange rates. 

Just wanted to clarify the advantages, obviously many ways to skin a cat. I'm a big fan of sealed hoods that exhaust outdoors, especially given some thing I read recently about digital ballasts causing MH bulbs to offgas toxic metals.


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## beeznutz (Jan 23, 2011)

right now I only have 2 plants goingand I'm not worried about smell so I'm not setting up for big yield just yet..
the reason I ended with the fan blowing on top was because I need the heat to stay in the room as is pretty cold and the idea was when the lights go off itll get pretty cold and the heater has to work more to keep up so if I was to have exhaust "holes" on top then it'll escape faster but (and this is my perspective, not saying I did it because so and so said it) if the exhaust holes are on the bottom then the heat will stay in the room longer, same goes for the humidity which is pretty low ( kinda odd for a basement....) and the humidifier runs 24/7 and still can't go past


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## beeznutz (Jan 23, 2011)

45% so that was the idea. also., the hood is on top of the room which will eventually (spring-summer) get hot so I figured the same fan/duct set up that blows in air right now will be used to hook up the the hood when the time comes eliminating unnecessary work later on.

everything that has been said and discussed on this post has been extremely helpful and informative and I'm greatful for everybody chiming in with their opinion and without getting into a "this is the wayto do it" type of discussion, so thx y'all 

so far everythingis fine and the girls are just exploding in size and they also look healthy. I'm still monitoring during lights off to make sure I'm good and yesterday after turningup the heat a little I didn't see temp dropping under 62 so it got better but it could b even better  that's just after reading the min/max on the gauge but I did check quite a few times while lights off and everytime the readout was about 72 so... what do you guys think as far as temp goes? during lights on steady @75 with min/max readout @72/79.
during lights off steady @72 with min/max readout @62/74.

eventually this what I want to get:

http://cheaphydroponics.com/store/view-all/cap-air-2-atmosphere-independent-temp/humidity-controller/prod_135.html


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## beeznutz (Jan 23, 2011)

forgot to mention, the fan blowing in air is on a timer with 45min off and 15min on every hour during lights off and constant on during lights on.


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## g13hydo (Jan 28, 2011)

whoever said you want more air coming in that exauhsting is fucking stupid lmao


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