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Having ventilation issues - First time grow box - Need some advice

ChefKimbo

Active Member
I swear I've done the research scouring this and other sites for information but I can't quite find a solution to this positive pressure issue I'm having.

Here is my box
24 cubic feet, 10 bulb CFL chandelier with more light to come on the side panels.
The exhaust is a 4 1/2" hole with an 80mm 12v pc pulling hot air towards the exhaust(at least in theory).
On top is a DIY 3inch carbon filter fitted with a 120mm exhaust fan, rated at 200cfm, on fan controller. The two exhaust fans share a power supply but just the 120mm fan is on the controller. I'm not sure if these fans are working together or not I would think it would be easy to tell.
At this window is a another 80mm fan pulling air in through insulated 6" ducting down to the intake.
The intake is roughly 8"by 5" fed by the 6" elbow here mounted with cardboard.
Inside is another 80mm fan temporarily placed to help circulate air in the cab.

The issue is I can't turn on the intake fan without creating positive pressure which defeats the purpose of the filter. This shed isn't air conditioned and temps can reach 90-95F early in the day This heat is stifling in the southeast. The cab is sealed well and the only openings are the intake, the door crack, and the two 1 1/2" holes for wiring and lights. The holes are stuffed with insulation while test are ran. :420:I'm trying to move air fast enough to cool the cab down to at least 85F without the without using the intake fan, but I don't see my plants surviving in the cab at these temps without good air movement. I'm stumped and out of ideas. I thought maybe adding another exhaust fan equal to the 120mm would help but would that would mean making another filter? I have another 120mm fan and a 60mm bad ass exhaust fan I pulled form an old battery charger. If I need more exhaust capacity what would be the best course of action? Any suggestions?
 

millertm

Well-Known Member
So, get a fan to push air in 6" hole from outside with speed controller. You will need another fan to push air out 4" hole. With 4" hole fan on full, back off fan feeding 6" with controller until neutral pressure.

I hope I understood your questions. You will need to use 2 fans, filter should be on 4" port inside box, with 4" fan pulling air through it.

Cheers
 

ChefKimbo

Active Member
Yes ok, i think you are telling me to put a bigger fan/controller at the intake in the window. Move the filter inside and place the fan outside on the 4 inch hole.
 

415friendly

Well-Known Member
I also had a DIY filter and temperatures that were in the high 80's. I bought a carbon filter off the internet and my temperatures dropped almost 10 degrees. It looks like you have the air passing through yours in a single layer? A store bought one will have much larger surface area allowing a lot more air to pass through it. The effectiveness of your top exhaust fan is probably limited by your DIY filter, and is probably pulling through a lot less than 200CFM, which is why your intake fan is creating all that positive pressure...The CFM of your exhaust is being reduced to lower than the level of your intake.

You can try taking the carbon filter off and seeing if your intake still creates positive pressure. If it does, then you've narrowed down your problem.
 

ChefKimbo

Active Member
I was leaning towards that being the problem. Originally I had 2 80mm pc fans at the intake, then I noticed the positive pressure as soon as I turned them on. I removed them and still got very little draw. The filter has two carbon filter sponges on each side seated in vented snap in drains and loaded with pellets. when I tested it seem to get good with but the evidence shows it cant out perform 2 80mm pc fans. Ill take the filter off and mount the fan to the 4" hole. Everywhere I read they always say your exhaust fan has to be bigger than the intake fan, if any. Luckily I ordered 2 fans and 2 controllers so ill change the intake fan as well.
 

415friendly

Well-Known Member
With a box that size, why bother with an intake fan at all? Your exhaust fan is on a controller, so you reduce the airflow if needed, or bump it up to maximum. The only reason you need an active intake instead of a passive is if, at the maximum setting, you're not getting the airflow you need and you're generating a lot of negative pressure, more than your passive can handle. You can also just drill a bigger hole for your passive intake :D or put some duct tape over the hole if you go too big. ;)
 

ChefKimbo

Active Member
The reason for the intake fan is to bring in cooler air from outside. Not really that cool but its gets up to 95F in this shed so to do something about the temps.

By a lot of negative pressure you mean the vaccum effect right? How would you know if your getting too much negative pressure?
I thought about making a bigger intake hole, the same size as the ducting to the window. Maybe this wil the pressure issue.
 

millertm

Well-Known Member
You need to increase air movement by force feeding you box. Your close but need to dial it some. My new tent is a challenge to keep cool due to low air volume like what your seeing. Rule one, more air.

Cheers
 

ChefKimbo

Active Member
I know I'm close man I can taste it!!! That's what I've been trying to do is get more air in, but with out the positive pressure.
 

millertm

Well-Known Member
I'm not sure I see any issue but possible smell with PP. Plant environment supersedes smell control because if your plants die it's game over. I'd look into a tent in the future or bore out that 4" into 6". I'm sure you'll get it soon.

Cheers
 

unforgiven

Plant of the Month: April 2016
some good advice already given.

I was leaning towards the diy filter being the issue as well. test it. remove the filter completely, hook up and run all your fans.

I know it is a cost issue getting all the new equipment when you start out, but if you try to even get one great exhaust fan, cheapo 4's go around a hundred bones. I just quick searched and found a 4" filter for 33 bones.

with those 2, you could possibly get away with just ducting for a passive intake from outside, if you can keep the distance short.

check out your options, and weigh your budget. do you already spend more than that on smoke? if so, think about the ramifications of being able to grow your own. that fan may be the only thing stopping you.

good luck,

and have fun eh
 

ChefKimbo

Active Member
The filter is not a huge deal right now because my plants are nowhere near flowering time, at least 2 months away. I put together that filter with the idea that it may not work very well in mind. I also have some ideas on building a bigger/better filter from spare parts I have. The exhaust is the main issue here. Originally I bought 2 200cfm fans and 2 controllers with the idea that I may need the extra fan somewhere either for intake or more exhaust. Everywhere I've read the intake should be atleast double the exhaust capacity. I haven't figured out how that does NOT lead to positive pressure. with a total of 6 fans ranging from 60mm to 120mm I figured I could move enough air to cool the cab during the day, at night the temp in the shed drops to around 82-84 so night time is manageable. Can you recommend another 4" fan if these are not adequate? Thanks everyone for your responses its been a big help!!

You are correct, the whole purpose of growing my own is to stop buying off the street and control my own medicines.
 

ChefKimbo

Active Member
Well everyone who mentioned the filter being the problem seems to be 100% correct. I removed the filter off the 4" hole, installed the 120mm fan on top and left the 80mm exhaust fan in the cab. WHAT A DIFFERENCE!!! The suction is actually spinning the 80mm intake fan in the window, even on the lowest speed. If I turn it up too high it slightly sucks the door inward lol!!! Much more air movement and no sign of positive pressure at all with the exhaust fans on. It seems that the filter was causing bottleneck and the exhaust fans were working against themselves. I can dial the 120mm fan down and still get suction with the 80mm fan. PROGRESS!!!:thumb:

Humidity has been lingering between 55-65% day or night, now its time to test temps with 10 lights on.

As far as the filter goes, millertm mentioned putting the filter inside the cab and have the 4" fan outside on the hole. As much as I hope this will work I can't afford to wait find out when these plant start stinkin up the place. I need to do some testing and possibly invest in a store bought filter. Always a group of teenagers hangin out next door and I don't want anyone sniffing the air and telling people what they smell.
 

415friendly

Well-Known Member
Since you're not opposed to having a "chimney" sticking out of the top of your box, you could also consider leaving the filter outside of the box. I've done a couple of quick sketches to show you what I mean. It's easier than explaining. :)



Diagram #1 is what is kind of standard, with carbon filter on the inside, but with the wooden cabinet, your box would support the weight of a chimney and you could save some valuable space inside your cabinet, as some of the filters can be larger than expected. I don't know how this would affect your soundproofing, though.
 

ChefKimbo

Active Member
Soundproofing isn't a major issue. The shed is more like a house. Wood frame and paneling with stucco, its the heat and the potential odor that worries me the most.
I had the other filter outside the cab , with the fan attached on top and another smaller fan in the hole. When I get a bigger better filter do I need to keep this configuration or change it?
 

415friendly

Well-Known Member
It's conventional to keep your carbon filter inside your tent/cabinet with the exhaust fan pulling air through the filter, because most tents have enough space to do that.

I'm not sure you need the other fan that is pushing air towards the filter because the air is moving directly from the cabinet to your filter. Most carbon filters don't draw through the end, anyways, they draw through their sides.
 

ChefKimbo

Active Member
Ah I get it now. The filters are built to draw air in thru the side for maximum surface area. Having the filter on the inside would be more efficient regardless of the size of the box. I'm going to be removing the smaller exhaust fan today and check things out. I have some ideas on how to build a better filter. Thanks again!!
 

unforgiven

Plant of the Month: April 2016
ok so I just watched the video which I am going to assume you used to make your filter, lol.

what I was trying to find was a diy that I copied a few years ago to make an inline filter, but no luck.

thought for a second this was the one I built but I have no cinder blocks lol


but this is what you want to style a filter after.


as said above, these filters are built to draw in through the sides. the center is hollow, basically a double layer of mesh, with the carbon in between them.

if you search diy grow room filter you can find them on other sites. I don't know about here, haven't tried.

but, and this is the big one.....

it didn't work for me. from 8 plants in a "sealed room" upstairs through hallways and more......if you walked up to my back door you could smell it if you got within ten feet of the door.

never again will I trust a diy air filter for what we do here.

wasn't average joe I was concerned with.......it was the off duty, hardass cop who powerwalked past my house everyday, luckily on the opposite side of the street. he may have caught a whiff, I never found out luckily.

call it my lesson learned.

the cost is really f.a. compared to losing all you have and going to jail.
 

ChefKimbo

Active Member
Lol, trust me I feel like a schmuck for believing that would work, desperation. But I'm glad its being dealt with now as oppose to when ill really need it. The second picture I'm having trouble perceiving the size of the can. If that's a 30-50 gallon can I may at some point experiment with that I have some spare parts maybe.

At the most I would like to harvest 1-2 plants at a time. Small topped, LSTed plants with decent yields but good quality bud. 1or 2 plants in veg while I'm harvesting. Just a few ounces while my plants coming to flower and seedlings behind them. The number of plants have to be kept down for the very same reason. Off duty cops, nosy neighbors and curious family members. I'm looking into building a drying box as well because the odor has to stay in check.

So I removed the inner exaust fan, 415friendly was right. It was just getting in the way the 120mm fan can handle the load easy even without the intake fan. From what I've read and seen internal fans to blow on the plants is a good idea as well so ill give that a shot. I'm glad we got past another road block thanks to your help everyone!
 

unforgiven

Plant of the Month: April 2016
if I recall the 26 cfm filter is around 12" tall. just search them you will find a plethora of can filters.

I did however find my diy filter and got some pics for ya. cloner too but that'll be in my journal.
it is a 6" inside diameter, flared to 8"outside. about 15"overall height.
you could do the same in a smaller size, but i'll tell ya, unless you have the right parts already, it cost me some $$$ to build. had I known then what I know now, I never would've thought twice about buying one.





the cloner lid is around 15" tall here


hope this helps,
have fun eh
 
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