Suck or blow pressure in 2x4 tent

[Mikedin]

I'm not dissatisfied with how things have gone with my negative pressure, and I have no plans to change it. Other than to steal your pantyhose trick. But it is a subject that vexed me from the start. I mean either way you are taking CO2 laden air and placing it in the tent. And if you use a CO2 tank to bolster the level around the plant(s) positive pressure might be better since negative pressure would just exhaust more CO2 into the room and away from the plant(s).

Technically that’s correct but when you feed Co2 into a room it needs to be sealed, one because you’ll otherwise be wasting Co2 but it has to be a sealed room (for burners etc, the little Co2 bags people hang seem worthless to me but idk lol)

But also when you introduce Co2 artificially you need to be very careful you’re not leaking that Co2 into your home potentially poisoning you … so in a Co2 addition application you’d have 0 pressure just a sealed room circulating normally they use a mini split, a heater, dehu as well as a humidifier to adjust VPD and Co2 concentrations in check without utilizing any external environment it’s all self contained, I believe they intermittently vent outdoors as well but I’ve never dug that deep past the potential Co2 poisioning and having your family in the home. Diddnt seem worth the risk to me

Also you won’t want positive pressure if you don’t want the house to reek like weed lol

 

[PianoStan]

Technically that’s correct but when you feed Co2 into a room it needs to be sealed, one because you’ll otherwise be wasting Co2 but it has to be a sealed room (for burners etc, the little Co2 bags people hang seem worthless to me but idk lol)

But also when you introduce Co2 artificially you need to be very careful you’re not leaking that Co2 into your home potentially poisoning you … so in a Co2 addition application you’d have 0 pressure just a sealed room circulating normally they use a mini split, a heater, dehu as well as a humidifier to adjust VPD and Co2 concentrations in check without utilizing any external environment it’s all self contained, I believe they intermittently vent outdoors as well but I’ve never dug that deep past the potential Co2 poisioning and having your family in the home. Diddnt seem worth the risk to me

Also you won’t want positive pressure if you don’t want the house to reek like weed lol

In my research before starting this grow, I read that studies have shown that marijuana plants can produce up to 300% more THC if you can raise the CO2 level from the atmospheric 400ppm to 750ppm. And that some people swear by getting their grow space to 1200ppm. So I was looking at going that route. Then I realized that I can literally reach out with my arm and touch the tent from the chair in which I'm sitting right now. And I decided it probably wasn't that great of an idea. lol

I briefly considered putting a bunch of plants on the wall where my tent's exhaust sits to deal with the extra CO2, but I wasn't sure that I could grow this plant, much less anything else. So the idea died.

 

[Canna_Digz]

I run full negative pressure on all my tents, all bottom flaps open and exhaust and filter at the top,

My tents are always pulled in even with all flaps open, in my 4x8 I have 4 flaps and I recently used one of the tent inlets to add in another piece of 6” flex ducting just to let a bit more air as well

The 4x4 has 1 flap so I added 2 of the 6” ducts as inlets at the bottom in there as well

As long as you don’t restrict the inlet you’ll have plenty of air exchange to remove heat and humidity as needed if you think it’s still too much negative pressure just throw in a 6” duct on a bottom tent inlet (I cover my ducts with panty-hoes so no bugs can get in through the ducting, at least that’s my method lol)

Whatever works

 

[Mikedin]

Whatever works

That’s how I see it! Everyone’s environment is different, does pressure matter at all? Hell, so many people don’t even use a tent just some fans blowing on them, or just outdoor in general, so just ambient pressure, end of the day I’d say both would work well, the real factors are rate of exchange as well as odor dissipation through exhaust filters, im the only smoker in my house, so I keep it odor free for the rest of the family, otherwise I probably wouldn’t even use a tent. Bonus of using a active intake is filtered air of any contaminants if you keep your filter on

 

[DougV]

Mikedin, I’m stealing the pantyhose trick, too. I’ve been using a screen, but pantyhose would filter better.

PianoStan, I’m a nurse, too. But I don’t have near your experience, just 10 years. I got bored not working after my first retirement, went back to school and ended up an RN. I’m an odd nurse, I worked in indigent care. But it was isolation rooms and odor control that got me questioning pressure. On my active system I have three inline fans. For an intake I have an 8” fan, for exhaust I have two six inch fans. On draws above one light, the other from my second light. All can be adjusted for air volume. By adjusting fans I can go negative, positive, or ambient air pressure. I use this tent for flowering. It’s inside a barn with no environmental controls and no concern with odor. Cold temps are easy to deal with. Heat, due to condensation, temps, and humidity was killing me. Changing to positive pressure and actively removing heat has extended my indoor season by 3-4 weeks, allowing me three full grows annually. (Veg is in a different tent.) I tried maintaining negative pressure, but I get 3 degrees lower internal temps with positive pressure. My guess is to maintain a positive pressure I have fans turned up and probably removing heat better.

 

[RoosterMan]

Well, that's a lot of information to take in, lol. I'm just getting started with this indoor growing, so I'm looking at everything I can. I currently have two grow tents going, and setting up a third. I don't have a "lung room", I have a bedroom, in s small apartment. Not much to work with. I've been trying to get a grip on my environment. Humidity and air pressure are two things I need to work on. And the reason I mentioned VPD, and am looking at it, is I've heard that negative pressure can cause the plants to suck up more nutrients than they need, and I might be having a little off that going on now. I haven't yet gotten into programming the controllers I have. I can usually just leave the fans on low, 2-3, and they're OK. Now that it's getting warmer, and more humid, I need to be turning my fans up. When I do that, it sucks the tents in badly. There's not a lot of intake, as I'm trying to keep as much light out of the tent as I. My idea was to use the existing fan controller to keep the temp and humidity in check, then maybe an arduino that will use sensors to measure temp and humidity, calculate VPD, and control a pusher fan on the intake to keep the negative pressure to a minium. I do still need odor control. Just a thought guys. Maybe overthinking it all, lol.

 

[Billybobbong]

So I’ve just set up an air intake just wondering do I set it so the tent walls are sucking in or bulging out
Do I set it so the exhaust fan is a bit stronger than exhaust fan or other way round thanks

I allways run negative pressure to stop the smell, using 2 centrifugal fans, one larger for exhaust,1 intake fan and prefilter attached to window duct, exhaust larger fan and twin carbon filters one small but high flow on the inside and one really big one outside... No smell

 

[Newty]

(I cover my ducts with panty-hoes so no bugs can get in through the ducting, at least that’s my method lol)

I use to use panty hose but now I use cut to size MERV8 filters from Amazon on the intake and also at the end of the exhaust duct, I use HVAC foil tape to adhere them. Before I started running intake fans, I would tape the MERV8 filters to the passive intake vents.

 

[Mikedin]

I use to use panty hose but now I use cut to size MERV8 filters from Amazon on the intake and also at the end of the exhaust duct, I use HVAC foil tape to adhere them. Before I started running intake fans, I would tape the MERV8 filters to the passive intake vents.
View attachment 2165342

Might do that for my bottom vent flaps! Thanks for the idea!

 

[Billybobbong]

I use to use panty hose but now I use cut to size MERV8 filters from Amazon on the intake and also at the end of the exhaust duct, I use HVAC foil tape to adhere them. Before I started running intake fans, I would tape the MERV8 filters to the passive intake vents.
View attachment 2165342

i gutted out an old carbon filter on my intake you can put this in a plastic tub and add a duct to your window, just seal this filter inside another box and use ducting this one is pictured in winter so no cold air intake required it's been disconnected from its box temporarily

 

[Billybobbong]

I also use an inline filter I made from an old tool box, this is great but hasn't got the same flow rate as the other.

 

[Billybobbong]

Yeh I use 6" centrifugal fans one 155w and the other 110 w, they run flat out but are connected to a thermostat so just com on and off whenever they want as set to the correct temperature for that grow period, it also activates the dehumidifier to, it's simple but work great in summer they run Nilly all the time it's just borderline Nilly to hot to grow, so I need heaps of air transfer.

 

[PianoStan]

Mikedin, I’m stealing the pantyhose trick, too. I’ve been using a screen, but pantyhose would filter better.

PianoStan, I’m a nurse, too. But I don’t have near your experience, just 10 years. I got bored not working after my first retirement, went back to school and ended up an RN. I’m an odd nurse, I worked in indigent care. But it was isolation rooms and odor control that got me questioning pressure. On my active system I have three inline fans. For an intake I have an 8” fan, for exhaust I have two six inch fans. On draws above one light, the other from my second light. All can be adjusted for air volume. By adjusting fans I can go negative, positive, or ambient air pressure. I use this tent for flowering. It’s inside a barn with no environmental controls and no concern with odor. Cold temps are easy to deal with. Heat, due to condensation, temps, and humidity was killing me. Changing to positive pressure and actively removing heat has extended my indoor season by 3-4 weeks, allowing me three full grows annually. (Veg is in a different tent.) I tried maintaining negative pressure, but I get 3 degrees lower internal temps with positive pressure. My guess is to maintain a positive pressure I have fans turned up and probably removing heat better.

I was a volunteer EMT/firefighter in high school, and before the military. Then I used my GI Bill to go to college for my RN. I bounced between infectious disease care (mostly TB and HIV/AIDS) and psychiatric nursing, but have also worked with hospice care. At first it seemed really strange having immuno-compromised patients on the same floor as highly contagious ones, but negative pressure isolation rooms for TB, and positive pressure isolation rooms for the HIV/AIDS patients. Then it was our job not to cross contaminate. That was my first job out of college, and it was still the early 90's. The AIDS epidemic was still new more or less. It makes me laugh to think about it today, but back in those old days as an EMT, Universal Precautions hadn't even been implemented yet!

I wish that I had the room to run multiple tents. But I live in a tiny apartment, and had to break down my home music studio in order to make room for the small grow op that I have. Interestingly, my tent running negative pressure is cooler than the air temp of the room. When I open the tent to look at the plant, the temp can spike 5F or more. (And I have a 2000watt Bestva led in a 3x3 tent).

Thanks for outlining your air pressure management. It gives me things to think about.

And i definitely want to thank the OP for posing the question. It's been quite interesting reading the different opinions.

 

[PianoStan]

I use to use panty hose but now I use cut to size MERV8 filters from Amazon on the intake and also at the end of the exhaust duct, I use HVAC foil tape to adhere them. Before I started running intake fans, I would tape the MERV8 filters to the passive intake vents.

Did you see a noticeable increase in tent temperatures? Those filters look rather thick, and like they might have the potential to decrease overall air volume. But they definitely look capable of keeping dust/pests away.

 

[PianoStan]

Well, that's a lot of information to take in, lol. I'm just getting started with this indoor growing, so I'm looking at everything I can. I currently have two grow tents going, and setting up a third. I don't have a "lung room", I have a bedroom, in s small apartment. Not much to work with. I've been trying to get a grip on my environment. Humidity and air pressure are two things I need to work on. And the reason I mentioned VPD, and am looking at it, is I've heard that negative pressure can cause the plants to suck up more nutrients than they need, and I might be having a little off that going on now. I haven't yet gotten into programming the controllers I have. I can usually just leave the fans on low, 2-3, and they're OK. Now that it's getting warmer, and more humid, I need to be turning my fans up. When I do that, it sucks the tents in badly. There's not a lot of intake, as I'm trying to keep as much light out of the tent as I. My idea was to use the existing fan controller to keep the temp and humidity in check, then maybe an arduino that will use sensors to measure temp and humidity, calculate VPD, and control a pusher fan on the intake to keep the negative pressure to a minium. I do still need odor control. Just a thought guys. Maybe overthinking it all, lol.

It seems like using a pusher fan would also have the benefit of blocking any light coming in through your intake hose. I expect that with my 3rd grow I will move from auto-flowers to photo-periods, and the ease with which light escapes through my intake hose has been one of the problems I've been trying to figure out how to address.

 

[Billybobbong]

It seems like using a pusher fan would also have the benefit of blocking any light coming in through your intake hose. I expect that with my 3rd grow I will move from auto-flowers to photo-periods, and the ease with which light escapes through my intake hose has been one of the problems I've been trying to figure out how to address.

I cover mine hoses in old tracksuit pants legs, stop any daylight getting in or light out you know, having said that my tent is wrapped in tarp and blankets in winter to keep stable

 

[Billybobbong]

Did you see a noticeable increase in tent temperatures? Those filters look rather thick, and like they might have the potential to decrease overall air volume. But they definitely look capable of keeping dust/pests away.

Yes and hence the fans are the most powerful I can get centrifugal fans pull harder than axial fan dose and it moves enough air, I have had to adjust filters to get the best flow, I could get better by adding a 8" external with an adaptor from 6" to 8, and increase the size inside or remove it, so far it works ok as is but yes you could definitely improve it but I think it's adequate. Runs about 4-5 C about ambient intake temperature with this 320w led. Summer is the worst but only just manageable

 

[Billybobbong]

Did you see a noticeable increase in tent temperatures? Those filters look rather thick, and like they might have the potential to decrease overall air volume. But they definitely look capable of keeping dust/pests away.

Yeh the external filter is 500 mm long 50 mm bed the internal is 20 mm bed and 500mm long not bad flow, one in the picture above is gutted and is a prefilter for intake the one under is the exhaust with the red sheet and under that the intake for the exhaust

 

[PianoStan]

Yes and hence the fans are the most powerful I can get centrifugal fans pull harder than axial fan dose and it moves enough air, I have had to adjust filters to get the best flow, I could get better by adding a 8" external with an adaptor from 6" to 8, and increase the size inside or remove it, so far it works ok as is but yes you could definitely improve it but I think it's adequate. Runs about 4-5 C about ambient intake temperature with this 320w led. Summer is the worst but only just manageable

I'm starting to see that growing weed can easily become a black hole in one's budget! I'm perfectly happy with the way my first grow is going, but every day it seems like some new way to get just that much closer to perfection reveals itself to me.

I wonder how my second grow will go. That will take place as soon as my current plant is harvested, but that means that it will be growing through June, July, and August. And my apartment can be 74F in February.

 

[Budtirement]

I have had the same 2x4 tent and equipment for the last 4 years. I have kept the fan and filter inside the tent, sacrificing that space.

When the filter is inside the tent, air enters the filter through the cotton cover and exits the filter inside on its way to the duct and fan. After each grow the cotton filter cover is dark with resin particles and needs to be cleaned.

If I move the fan/filter outside the tent then the air would be moving through the filter in reverse, from the tent through the duct to the inside of the filter to the outside, bypassing the cotton cover.

In my mind I imagine the carbon inside the filter getting dirty faster without the cotton to act as a first stage filter. Also, the surface area of carbon exposed to dust and resin particles is less on the inside circle of the filter then the outside circle.

Is there a difference in carbon filter life expectancy based on position inside or outside of the tent? How about the fan, if the fan is positioned before the filter, does it get gummed up faster?