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How to exhaust my 4x4x6'6" grow tent?

  • by halitzor
  • Jul 30 2009 12:28 PM
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  • urban farmer

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Posted 30 July 2009 - 12:28 PM

I picked up a used 170cfm 4" exhaust fan locally on the cheap. The way I have my room setup (not growing yet) is this:



4x4x6'6" grow tent

Directly behind it is a basement window that I boarded shut with plywood and sealed it. (the window is gone).

I have the exhaust flange on the bottom right side of the board, and the intake flange on the top left side. I connected the fan to the board via the flange and connected my foil ducting to it which goes into the top of my tent and down.

I had the other side hooked to my glassed reflector, but it didnt seem to be doing much for the room temp so I unhooked it. Instantly the sides of my tent started to suck in.

So I know its exhausting well, but it doesnt seem to be pulling any intake air in from the other foil ducting. I figured the negative pressure would cause the intake ducting to draw fresh air in from outside. If it is, its barely doing it.


Should I put the fan INSIDE the grow tent? I could probably rig it up if I needed to that way.



I have a 600w glassed lensed reflector. It has a duct flange on the very top and one opposite the side of the bulb. Should I exhaust the air from the light itself? Or just from the room in general? It seems to work better when its just hanging into the room to me.


Thanks!
Replies (44)

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  • Osho
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Posted 30 July 2009 - 02:42 PM

Hey man,

The size of your grow space and the capacity of your fan (especially if it is not air tight other than the ducting) will not produce enough negative pressure to create a reliable draw from your intake vent. Not to mention that you should be creating positive pressure rather than negative pressure, as this will produce a more sterile environment (pharmaceutical companies use Positive Pressure for all of their clean rooms, as do hospitals).

Place a powered fan on your intake as you will need much more fresh air than you are currently providing. Taking all the air out without a STRONG feed of fresh air will thin the air and help in retaining more heat. Fresh air is key mate, KEY!

You had stated that your exhaust fan was on the low side and your intake was on the high side. You need to switch them as hot air rises, and taking air from the lowest point in your room will take out all the cool air. General rule of thumb.

Try to create an even balance between both your intake and exhaust. Clean, fresh air will help your plant in so many ways, and the proper exhausting of that room (from the TOP of your room not the bottom) will prevent too much C02 from building up within the environment and reduce the heat factor immensely.

Try splitting your exhaust vent ducting inside your room so you are taking heat from your lamp (makes a world of difference with the heat) and your room.

Leaving all electronics outside or minimality with the amount of electric appliances inside your room is much safer and helps with maintenance as your plants will not be stressed if you need to access one of your appliances (fan, ballast, etc.)

Here's how I run mine.
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Posted 30 July 2009 - 02:46 PM

I'm not sure but if youre using a 600 watt fixture in that space imo you will have to up your cfm's. Presently have same wattage in a bigger area & using 2 1000 vortex one in and out, hooked to temp controled plugs, they almost always maintain the set temps but they do climb @ times, your basement set up is cooler than mine but I would def up the cfms and get 2

Good luck

  • urban farmer

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Posted 30 July 2009 - 03:25 PM

My tent isn't getting hot. I've had the light on for a 5 days straight on a bag seedling (for a house plant) and its only 82 inside with the fan off.

I dont think you read my post correctly.


I have one basement window with both ducts connected. The exhaust is in the bottom right of the window, the intake is in the top left of the same window. There is a separation between the two sides. Only maybe 1.5 feet of height difference between the intake and the exhaust. THe window is at the top of my tent.


I have the exhaust going out of the TOP of my tent, and out the window.

I have the intake going out of the TOP of my tent, and coming from the same window.

I have a ductstat (wayyyyyy cheaper than the controllers you guys are using) coming in the mail that will go inside my tent and control the fan to maintain set temperature.



Let me draw you a picture.....

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Posted 30 July 2009 - 04:02 PM

That is exactly what I stated, I read your post correctly the first time, and please remember, I have been doing this for over 15 years now, so I know most my stuff ;)

Your exhaust ducting is LOWER than your intake ducting, that's bad. You should cut your exhaust ducting so its at the highest point of your room, and extend your intake to the room so the duct feeding air into your room is lying on the ground. Intake = cool fresh air, and heat rises. If your taking air out of the room lower than whats being fed into the room, your just sucking out all of your cool clean fresh air and leaving the hot un-enriched air to linger at the top. Please remember that im only trying to help!

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Posted 30 July 2009 - 04:25 PM

That makes more sense, maybe we should only communicate via pictures? Haha



I can easilly switch which side the intake and exhaust is on the window, I don't have a duct hole near the bottom of my tent, but there are 3 air flaps (i duct taped them shut)

I guess in reality I could just open them up and remove the intake duct all together?



Or I could cut a hole in the tent and glue a flange to it and attache the ducting that way, what do you recommend?


BTW how big is your tent and how has your experience been?


I should be getting my super silver seeds in the mail today or tomorrow, bout to start!

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Posted 30 July 2009 - 04:41 PM

6'x6'x6' - With the setup shown in my pics its amazing. My ac unit has an auto on/off controlled by thermostat. I just extended the thermostat so it turns on and off according to the inside temperature, which is max 80 degrees.

You need air coming in from outside, preferably filtered and cooled*******

How you have your ducting going INTO your tent isn't the issue at all, leave the holes where they are.

Like I said, inside of your tent you just need to shorten your exhaust tube so the ducting is drawing from the highest point, and extend the intake ducting so the tube is lying on the ground.

If you are using this tent then un-duct tape the vents. They are there to produce upward draft for better air circulation (moves heat upward faster so cool air can be more prominant.) Please don't cut your tent, lol.

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Posted 30 July 2009 - 04:51 PM

I must be confused because if you vent a 6oo watt fixture in a 4 by 4 by 6ft tent with only a 170 cfm fan the only thing I can think of is the basement is in Alaska

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Posted 30 July 2009 - 04:58 PM

FRANKLY 170cfms is perfect. 4'x4'x6' is only 96 Cubic Feet. If it can move almost twice the area of air per min, hes beyond being on the money. Hes fine, lol

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Posted 30 July 2009 - 05:16 PM

Considering the sides of my tent suck in like a cheap hooker, I think my CFM's are fine for this tent lol.




Osho, keep the advice comin bro!


I might make a way to connect the intake ducting to one of the circulation flaps. I would rather do that than buy another long piece of overpriced foil ducting. (a hardware store here sells it for 99c a foot tho so maybe I will get a longer one.


My intake air should be filtered you say? How / why? Its coming directly from outside. Temps in my tent dont seem to be a problem even with the fan off, so I think I'll be ok just using outside air.


My basement is a constant 69 degree's (at least my res water is) so should I duct the air in from inside the basement? I have a pet rabbit down there so he's making a lil CO2! (I know its not anywhere near enough to affect anything, just saying)



About CO2, i'm def not ready to start using it. But I can get a full 20lb aluminum tank for $100... think I should do it?

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Posted 30 July 2009 - 05:34 PM

How about you cut the exhaust tube down some so its literally right where the tube comes into your tent and duct tape the cut ducting tube to the intake side.

It should be filtered 1, to prevent bugs from crawling in, and two, so your not getting any air borne diseases, or bacteria (there is plenty man plenty) into your room. Just pure filtered air. Buy a thin air filter and a screen and just cut a piece and fit it over the intake duct outside your boarded window and tie it around the ducting with a zip tie.

Res water and air temperature are always going to be different from each other. Your res temp should be 65 degrees (pour a little cold water to lower it) to prevent algae buildup or root rot.

Get yourself a Thermometer with a built in hygrometer (Measures Relative Humidity which should be 60%). CVS or Walgreens/Walmart/K-Mart . . . whatever. . . has them for 10 bucks max.

You only need the C02 when your flowering so hold off for now, get through your veg phase, see where your at. I make home made C02 from yeast and sugar mixed in water.


$100 for the tank, then you need a pressure regulator, and tubing, and a way to hang the tubing. And btw, since you NEED a pressure regulator for the tank (which requires power) I'll have you know that they are about $150 bucks each.

Yeast + Sugar w/ Water = 5$ lol

Edited by Osho, 30 July 2009 - 05:37 PM.


  • urban farmer

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Posted 30 July 2009 - 05:43 PM

How does the homemade co2 method compare to the real thing?


And for a co2 setup, I would have to get the regulator AND the controller so it would be about $550 additional :)




I like the cheap idea tho... and I'm definitely going to put a filter on the intake and exhaust, I just realized any bug can just waltz right in.....


BTW, I'm goint with an external RES and planning to use 4 buckets in my tent. Do you think its necessary to have all the water circulating or will the air stones suffice?

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Posted 30 July 2009 - 05:53 PM

My C02 method here at home works good for me. That whole c02 setup is too costly and i could find something much better to spend it on.

I take it each bucket will be linked to your res? If so, having your air stones in the res and then pumping the water to each bucket during feeding cycles will work fine. Just connecting all your pots to your res with no fill or drain cycle daily won't circulate water, you need to create flow so that oxygen enriched water can go to each bucket, unless each bucket is self contained (no res connection, just Deep Water Culture (DWC)). In that case you will need at least one air stone in each bucket.

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Posted 30 July 2009 - 06:19 PM

I have 4 airstones almost the size of a soda can :)


One for each bucket, but I think I might need one in the res too. What do you think?


Want to take this convo to PM?

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Posted 30 July 2009 - 06:33 PM

Hey man,

The size of your grow space and the capacity of your fan (especially if it is not air tight other than the ducting) will not produce enough negative pressure to create a reliable draw from your intake vent. Not to mention that you should be creating positive pressure rather than negative pressure, as this will produce a more sterile environment (pharmaceutical companies use Positive Pressure for all of their clean rooms, as do hospitals).

Place a powered fan on your intake as you will need much more fresh air than you are currently providing. Taking all the air out without a STRONG feed of fresh air will thin the air and help in retaining more heat. Fresh air is key mate, KEY!

You had stated that your exhaust fan was on the low side and your intake was on the high side. You need to switch them as hot air rises, and taking air from the lowest point in your room will take out all the cool air. General rule of thumb.

Try to create an even balance between both your intake and exhaust. Clean, fresh air will help your plant in so many ways, and the proper exhausting of that room (from the TOP of your room not the bottom) will prevent too much C02 from building up within the environment and reduce the heat factor immensely.

Try splitting your exhaust vent ducting inside your room so you are taking heat from your lamp (makes a world of difference with the heat) and your room.

Leaving all electronics outside or minimality with the amount of electric appliances inside your room is much safer and helps with maintenance as your plants will not be stressed if you need to access one of your appliances (fan, ballast, etc.)

Here's how I run mine.
Posted Image
Posted Image


+rep

Great post! Excellent advise about the positive pressure. That is another one of those misconceptions being spread through GC. Negative pressure is exchanging air before your plants get to benefit from the fresh c02. More air coming in than out!!!:smoking:

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Posted 30 July 2009 - 06:39 PM

No need for PM, people like to read stuff like this, I know I do. The more O2 in your water, the better. Helps root growth explode, and algae cannot thrive in the environment enriched with oxygen. I'm more concerned with how your hydro system is at this point, care to share?

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Posted 30 July 2009 - 06:49 PM

Sure, my pre drawn pics are at home though. So I'll have to use words :)




I have a 25 gallon roughneck rubbermaid container with lid as my res. (it probably holds about 15 gallons up to the max water level 1" below my net pots.)

This is outside of my tent, I have a 1/2" grommet in the side of it with a 1/2" black straight connector coming out of that. I have black 1/2" ID tubing running from about 1" high from the bottom of the res, to the same height on the first bucket.

The first bucket is plummed the same way into the 2nd bucket, 2nd into 3rd, 3rd into 4th.

I have shutoff valves between each bucket and between the first bucket and the res.

I'm using dark gray/silver 5 gallon buckets (light proof) with black bucket lids with built in 6" net pots.

I'm using hydroton? as my medium with rockwool plugs that I will be starting my seeds in.



I will be changing out the water every 2 weeks or until I go through 15 gallons, which ever comes first.


I'm using the Lucas method (modified by rumpleforeskin) with GH floramicro and grow or bloom, cant remember which right now. Thats the modification, rumple says one of the 3 is useless basically, and he gets like half a pound or more from 1 plant, so i trust his judgement.

I have a hanna ed/tds/ph tester (135 shipped on ebay)
Its calibrated already


I have ph up / down of course. My tap water is about 7.5 ph out of the tap so I don't have to down it too much thankfully.

I will be getting R/O later.


Let me know if you NEED picture, I think thats about everything though.


For my first grow, I'm not pissing with carbs or bloom enchancers or anything. I just want to get the system down before I dive into that can of worms.

I'm thinking about getting a few 16w 268 LED triband bulbs from HTG supply (30 shipped I think) for extra lighting during flower. I'm doing this because I don't think the 1 600w HPS is going to provide enough light to the 4 corners of my room.

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Posted 30 July 2009 - 07:09 PM

I think your res would be pointless to be honest. Rumples solid state bucket setup works fantastic, I tried and and am currently running it again, lol. Try using your res only for filling and draining and keeping the buckets separated from one another as far as water circulation goes. It sounds as though you have a pretty good idea of where to start. No res would save you so much work dude and having one wouldnt make any bit of difference really.

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Posted 30 July 2009 - 07:32 PM

Rumple actually told me otherwise, he said you can go solid state, but you have to monitor each bucket individually, and add water constantly.


He said with a res the only difference is in how often you need to completely change out the system. Since theres more water and more nutrient solution, you have to do less monitoring / work.


Each bucket only holds 3.5 gallons, and during flower they will drink a gallon a day. That won't allow you to keep the nutrient solution 1" below the net pots like rumple recommends, because it will constantly be going down.

If you have a large res however, the water level will drop MUCH slower.


Am I offbase?

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Posted 30 July 2009 - 07:38 PM

True, I just hate toting all that water in one bin. lol

I mean other than a good top off method I wouldn't find a use for it.

Its your first home made grow man, its all about what YOU want to do this time around. Just trying to give the friendly nudge. Try out a res system, who knows, you might love it.


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