Negative vs. Positive pressure in tent


They should be good to put in the tent.

Just be careful not to overwater.


I had a intake that was overpowering the exhaust system it was really blowing up the tent and it definitely leaked the smell. It just didn’t seem right looking that way lol I’m using a Gorilla tent and it still has little light leaks too and so I put a weaker intake and don’t smell a thing. Intake is on the bottom blowing on plants and exhaust up top. 600 watt led and it gets hot and my temps are mid 70s. The air being exhausted is quite warm too. Although it has been cooler outside than usual. It’s early august and feels like fall.


@garberfc sorry I was slow to respond. But yes, I would agree that you want to exhaust from the top. It seems like you already figured that out with the others, awesome!

What you really don’t want to be doing is pulling the warm air generated from your light back down through your canopy. It’s much better to grab the air from the bottom (should be the coolest) and pull that through your canopy and then exhaust out the top. There are probably always going to be some exceptions, but I believe 99% of growers exhausted from the top of their grow area.

At 48" with your light, watch for them to start stretching. As soon as you see it start dropping that light, you don’t want them to get very leggy.


As usual. My boy @dbrn32 is on point.

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Thanks for all the help and advice. I have my tent dialed in at 81f, 41%rh.

I’m keeping my seedlings moist with an eye dropper and mister. A couple of squirts every two hours helps keep the MG seedling soil moist.


I’m not familiar with the different types of MG soil, but I know you need to watch most closely. Consider changing to a different brand of soil if you transplant.

I’ve read up that they can be ‘hot’. The version I’m using has NKP at .03/.03/.03.

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I didn’t see anything about time release nutrients in the description, which is typically the issue with miracle grow products. Hot is usually relative, and can be offset by waiting on any additional nutrients, and watering to runoff if need be. I think you’ll be fine if you just keep an eye out for any issues.

Am I the only one that thinks that ZERO pressure, as in having unrestricted airflow, is best for plants? With regard to mold, smell, whatever - having an even and thorough exchange of air is the goal, and any pressure whatsoever indicates a deviation from that.

Just sayin…

I agree with you if smell isn’t an issue. Not to mention it’s really difficult to actually get there, and even more difficult to maintain.

Otherwise, no. It’s really simple to create a negative pressure condition and the best condition to run under if you’re trying to control scent. Besides it being pretty much the only way all the air in your area wanting to move toward your exhaust, thus being more proactive on safeguarding from mold.

I understand what you’re saying @Whodat66, it just doesn’t really work that way. Think about growing outdoors… that’s essentially a pressure neutral condition, and mold is a huge issue for outdoor growers. Granted, it’s really more of being able to control the environment. But since we can control the environment indoors, we may as well do it well.

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Yes, I understand that. But for most indoor growers (not garage or shed) the climate is already controlled! The only “control” really needed is to adjust the factors added by the tent. Your closet most likely will not randomly mold. Add a moisture rich growing environment, then lock that in a small space, and you change that.

I sympathize with those worried about the smell, and I still think that the goal would be a filter that works, and keeps the air flowing. But my grow in a closet without a tent makes it easier IMHO, than having a smaller enclosed space like a tent. With the thermostat set at about 73, my lights and the lack of designed ventilation in a closet make it a steady 80 degrees, and the little fan blowing across the plant tops makes the grow area about 79. When the lights go off, I open the door and let the temp get back to normal, then close it for the night. The less you have to adjust, the less there is to go wrong.

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Interesting stuff here lads, I think if you have positive air pressure then your tent would eventually blow up like a balloon, but usually there are air holes or flaps ect where it would escape, thus like someone above said kick air out before it could go through the carbon filter creating smell. However. Some strains don’t smell super super strong, and if it’s only one small plant just get a carbon bag, paid like 20 bucks for mine and it’s stopped smell for ages with 11 plants. Do also have a carbon filter ect but I’m telling you those bags work! GL



Can you provide a link to a carbon bag?

Not the one I have but that’s the type of thing your looking for. It’s the same stuff they put in carbon filters that absorbs smell


My bad something like this

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Interesting. Glad to hear you used it and it worked so well. I may look into getting one if i have an odor problem.

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I disagree that most indoor growers don’t have issues with temp and humidity. In my experience, most do. At least until they get their space figured out. My house is steadily kept at about 71 degrees and 50% humidity regardless of season. Put any of my lights in a tent, and temp inside of tent will easily hit mid 80’s or more without ventilation. Throw in a hydro set up or a few pots of soil that are regularly watered, and there goes the humidity too. Like you said, confined in a small space makes a huge difference, it doesn’t have to be limited to a shed or garage.

If you grow in a closet, then you’re prone to light leaks. Especially if you open the door at lights off. Most people don’t want to be limited to growing autos, hence the reason for the tent. And the smell, that’s a whole different issue. No matter how little of a deal it is, I wouldn’t want my entire house smelling like weed.

If you have something that works for you, run with it. But your set up isn’t idealistic for the majority of growers.


Not saying it is. Just saying that if you grew in the middle of your living room, you would have fewer issues than in a closet, fewer in a closet than a tent, etc.

Which is why I said “the climate is already controlled! The only “control” really needed is to adjust the factors added by the tent.”

If I grew in the middle of my living room each and every one of my plants would herm or never bud. You understand that right?

So talking hypothetical in this case is pretty useless. That’s all I’m trying to say.

Just saw this post it will be easier to control smells from the grow room or tent with a negative pressure you can achieve this using a speed controller on intake fan to slow it down to about half speed
Positive pressure will not prevent mold or anything else except maybe dust and dirt
Mold grows when you don’t have enough air flow in a given space if you have a negative pressure it because you are exchanging your air efficiently
This is why most commercial buildings are keeped in a negative pressure i.e. Revolving doors in larger commercial buildings this is because you would have a hard time opening a Normal swing door cause of the vacuum
So I recommend you get a speed controller and run your intake at about half speed of your exhaust
Example if you have a 190 cfm exhaust fan you should be running Intake at 80-90 cfm walls of tent should be pulled in slightly
Hope this helps @garberfc