Negative pressure tent - advice needed

Hello everyone

I have a 4x4 tent and use intake and exhaust fan (exhaust is twice as powerful as intake) so it does create negative pressure..

However the walls on my tent are gettig 4-5inches inside due to negstive pressure on each side thus reducing quite a lot of growing space.. any idea on how I could strech the tent so the wall dont push too much on the inside.. i could reduce the negative pressure by adding a bit more air trap at the bottom but I dont think it would change anything to my situation except taking a bit longer for the wall to come inside.. i had the idea of adding plumbing pipe insulation on my 4 pole which would stretch the fabric a bit more but not sure it would make a big difference.. so before I try that I was just wondering if anyone had any idea how I can fix this?

Thanks

You could get a fan controller and reduce exhaut fan until it pull less on the side but not too much so you wont loose neg pressure... Or you could add more "crossframe" between the vertical tubes. You can take a pvc pipe two hole at the end and tie wrap it to the vertical tube if you see what i mean?

I Have an home made tent wich the front is about 5x5' and it has no crossframe. The wall suck in about 2inch... but the exhaust fan is not that powerfull but enough to create neg. pressure.

Glenkush said:

You could get a fan controller and reduce exhaut fan until it pull less on the side but not too much so you wont loose neg pressure... Or you could add more "crossframe" between the vertical tubes. You can take a pvc pipe two hole at the end and tie wrap it to the vertical tube if you see what i mean?

I Have an home made tent wich the front is about 5x5' and it has no crossframe. The wall suck in about 2inch... but the exhaust fan is not that powerfull but enough to create neg. pressure.

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reducing exhaust is not really an option unless I put a timer, both my intake and exhaust fan have controller but my intake is 4inch and running at 100% and my 6 inch at minimum still pull too much to my liking but temps and humidity has been under control so didn't want to mess too much with changing air circulation for now.

I get what you mean by crossframe between the vertical pole and the 2 hole on pvc pipe, does sound like a good alternative too, I was worried to put something on the wall as it would lowered the reflection of the light, but 2 not too big pipes should not change much and also provide some space to attach fans or something else if needed. thank you for the idea

I'm not sure why putting a controller on the exhaust fan is going to cause you to need a timer? If your exhaust is creating so much negative pressure that it's pulling your tent walls in, it's probable that it's just overworking that fan, using more electricity, and not accomplishing anything, except the problems you mentioned. And if both fans have controllers already, why not just lower the exhaust until their slightly more balanced and not creating excessive negative pressure? I could be missing something, but it seems logical, lol.

fearnoevil said:

I'm not sure why putting a controller on the exhaust fan is going to cause you to need a timer? If your exhaust is creating so much negative pressure that it's pulling your tent walls in, it's probable that it's just overworking that fan, using more electricity, and not accomplishing anything, except the problems you mentioned. And if both fans have controllers already, why not just lower the exhaust until their slightly more balanced and not creating excessive negative pressure? I could be missing something, but it seems logical, lol.

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what I meant with the timer is it could go on for some time and off some other time.. but just fixing the problem for the time the fan is off... lol

I said that both my fans already have controller.. but my exhaust fan with the controller at minimum and my intake fan at maximum still create too much negative pressure..

*edit - I'm not saying too much negative pressure because I guess it may not really be a term.. just that my sidewall on my tent are making me loose quite some space at 4-5 inch on each side it's as if my 4x4 tent was instead a 3x3 tent.. I'd like to use all the space.. or just say most of it..

Ah-so, I missed the one on minimum... well, if there's too much negative pressure, is it possible to leave the tent door slightly unzipped or are there like window flaps? Oh wait, would that create issues cuz of light seepage? I keep forgetting why people use tents, lol, I just grow in my basement in a spare room when I'm not growing outdoors. Hmmm, well one time I designed a basement grow to take in make-up air through a hole I cut in the door - fitted it with a filter and then built a double baffle, one on each side and painted flat black so light would get in, but that's probably not much use, lol. I pretty high right now, so probably not much help

Could always use some stiff wiring in between poles to hold it out.

They have these thermal boards at Lowe’s, kind of foam boards with reflective material , you could put those in . They come in 4x8 so they could stiffen up the sides if you get me. Anyway I’ve been planning to do that since I have the same problem you have

sdd420 said:

They have these thermal boards at Lowe’s, kind of foam boards with reflective material , you could put those in . They come in 4x8 so they could stiffen up the sides if you get me. Anyway I’ve been planning to do that since I have the same problem you have

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Thats interesting ill look into that too

I added 2 rows of 1inch alum angle about 2 feet and 4 feet from the bottom...keeps the tent side from sucking

Here are a couple of shots, hope they help. without these, the walls would suck in by 3-4 inches each side at the deepest point, now, maybe an inch at the deepest point.Hose clamps are your friend (I used shrink wrap to cover the sharp end).

Zero_OS said:

Here are a couple of shots, hope they help. without these, the walls would suck in by 3-4 inches each side at the deepest point, now, maybe an inch at the deepest point.Hose clamps are your friend (I used shrink wrap to cover the sharp end).View attachment 4103218 View attachment 4103219 View attachment 4103220

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That's ingenious
going to have to use that
Cheers
CCG

Zero_OS said:

Here are a couple of shots, hope they help. without these, the walls would suck in by 3-4 inches each side at the deepest point, now, maybe an inch at the deepest point.Hose clamps are your friend (I used shrink wrap to cover the sharp end).View attachment 4103218 View attachment 4103219 View attachment 4103220

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That looks perfect thanks for sharing the pictures

Glenkush said:

You could get a fan controller and reduce exhaut fan until it pull less on the side but not too much so you wont loose neg pressure... Or you could add more "crossframe" between the vertical tubes. You can take a pvc pipe two hole at the end and tie wrap it to the vertical tube if you see what i mean?

I Have an home made tent wich the front is about 5x5' and it has no crossframe. The wall suck in about 2inch... but the exhaust fan is not that powerfull but enough to create neg. pressure.

Click to expand...

Thats probably the easiest way to handle it. That other way above is nice, but overthought in my opinion. my tent has a little window on the bottom with a screen. I leave that open all the time ( I also laugh at all the conversations about light leaks too due to that) and that evens the pressure.

I ended up building a cage to my tent with pipes i attached my scrog net to it.. there is still a bit negative pressure in the topper portion of the tent because the 2 are close to one another but it doesnt matter to me at my plants height I have my full tent size
I am very satisfied with the result

I’m lost as to why you can’t put a controller on it and turn it down until the walls don’t dip in so much, I have one on each fan (inlet/outlet) and adjust them so the pressure is not too much, it’s also useful for temps aswell

Ah just read above, seems you may have the wrong size fans if one on minimum is out doing the one on max. Also when you put a filter on the exhaust it will lose a lot of pressure

DrGrinspoon1010 said:

Ah just read above, seems you may have the wrong size fans if one on minimum is out doing the one on max. Also when you put a filter on the exhaust it will lose a lot of pressure

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Yes exhaust is twice as powerful than the intake.. thats what I had read before buying them as being the "norm"........ that being said I think many dont even use intake fan i could probably got away without it by just opening more air intake hole but didnt do it.. lol I didnt expect the difference to be that much of a gap.. but with the cage i can maintain same airflow and keep my tent sidewall straight and didnt cost much to do.. i also have now more places in my tent to attach fan and my scrog net.. so it all played out well in the end

I didnt mention it but I used 3/4 size pipes. i felt 1/2 may have been too flexible for my need and 1 inch semmed a bit too big..

fwiw, when I didn't have my cross bars, even at 20%, my fan sucked the walls in (passive filtered intakes), so if you run any neg with the fans, the walls would suck in if there is slack in your tent walls. It could be that DrG10's tent has little slack so a fan on low is all he needs. I have a vivosun, and there is a shiatload of slack.

@Viceman666 are the cross bars held up by friction? I didn't see any ties at the corners or supports.

Zero_OS said:

fwiw, when I didn't have my cross bars, even at 20%, my fan sucked the walls in (passive filtered intakes), so if you run any neg with the fans, the walls would suck in if there is slack in your tent walls. It could be that DrG10's tent has little slack so a fan on low is all he needs. I have a vivosun, and there is a shiatload of slack.

@Viceman666 are the cross bars held up by friction? I didn't see any ties at the corners or supports.

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I have a vivosun tent too so that might be the common issue lol.. i put tie in the corner on the top one only the smaller one is tight enough to hold by itself the one on top is tight too but a bit looser but both of them i can adjust the height easily.. there is a tie on each end