Positive vs Negative Tent Pressure

HugePeckerhead

HugePeckerhead

Well-Known Member
I see conflicting answers everywhere I look. Is it better to have positive or negative air pressure in a tent? I understand if you're scrubbing the air you want negative, but if you're not using any filters because smell isn't a factor then does it really matter what the pressure is as long as the air is being moved and the temps are right?
 
HugePeckerhead said:
I see conflicting answers everywhere I look. Is it better to have positive or negative air pressure in a tent? I understand if you're scrubbing the air you want negative, but if you're not using any filters because smell isn't a factor then does it really matter what the pressure is as long as the air is being moved and the temps are right?
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I was having a bit of trouble with heat in the tent. even with the ac in the room with it. i tried to leave the side flap half open. it was just wavering and fluttering rather than being pulled into the tent. and that's when i finally got my temps in check during that grow.

I haven't figured out how or why it made such a dif, but haven't put much thought into it either.
 
Remystemple said:
I was having a bit of trouble with heat in the tent. even with the ac in the room with it. i tried to leave the side flap half open. it was just wavering and fluttering rather than being pulled into the tent. and that's when i finally got my temps in check during that grow.

I haven't figured out how or why it made such a dif, but haven't put much thought into it either.
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My temps are a little funky right now in my tent. It's my first time using one. I only veg in it too. I can keep them well within optimal range but just kicking my humidifier to up that just slightly. I have great airflow too but it had me wondering if the pressure matters at all as long as the temps and air are in range.
 
I have positive just slightly as I push air from my room into the tent. I have 2 fans inside the tent too. No fans push air out but the top duct and the screen I opened to allow air to escape.
 
I'm pretty sure unless you're trying to keep all the smells going in the same direction negative pressure doesn't matter at all. just lots of air flow and temps in check is good. even with it being legal ( ish ) i still try my best to cover up the smell. didn't really work this last time during harvest i turned off the exhaust fan / scrubber and it smelled up the restaurant downstairs pretty bad for a bit lol.
 
Remystemple said:
I'm pretty sure unless you're trying to keep all the smells going in the same direction negative pressure doesn't matter at all. just lots of air flow and temps in check is good. even with it being legal ( ish ) i still try my best to cover up the smell. didn't really work this last time during harvest i turned off the exhaust fan / scrubber and it smelled up the restaurant downstairs pretty bad for a bit lol.
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I can keep the smells in check but RIP to the room I trim in too. I didn't really think the pressure made any difference as long as her environment is optimal.
 
Negative is better than positive. But you don't want an abundance of either.

Your changing the atmospheric pressure at that point. More negative mimics higher elevation, more positive mimics closer to or below sealevel.
 
Hey guys just bringing this one back to life again. Just changed lights and it does not run warm at all....which is a good and bad thing because now my tent is staying at around 23c 74f during lights on....and around 18c 64f during lights off.

I have 3 fans in my 4x4x8 tent, 1 small one on the upper left corner on the ground, a medium on the opposite side bottom right on the ground, and a oscillating fan blowing at the canopy level. I have my exhaust fan running every 45 mins to get fresh air in and this is the only time there is negative pressure, otherwise it's always positive pressure.
Would it be a bad idea to run the exhaust fan every hour or 1.5hrs? Would this not provide enough fresh air into the space? I heard there should always be fresh air every 2 minutes or so....but because i have positive pressure I'm assuming no fresh air is entering the tent until the exhaust fan kicks in.
 
NeoScott said:
How are you feeding air into the tent? A positive pressure tent has something blowing air into it causing an increase of pressure. If your not moving the air in or out it’s a stale system and there no exchange of air besides the heat increasing the airs pressure and your fans moving it around(but not out)
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My exhaust fan runs every 45 minutes for 15 minutes which then will exchange and bring fresh air into the tent through the bottom vent which is open. I could try for every 30 minutes but because my basement is around 18c, it brings the tent temperature down to that as well. So this is the only fresh air that the tent is getting.
is 45 minutes for air exchange too long even though it doesnt get too hot or humid in there?
 
Air exchange is about co2 and not really about the heat/humidity(just a bonus) Hyper ventilate into a paper bag and see how long until you feel week or dizzy. You’ve used to much of the oxygen and it’s time to get more into the bag. Same deal with your plants. Except co2.

I run my fan /all the time/ during the winter in Canada with no heater I get the same digits you do. Last night was cold and I dropped to 17. Keep your room warmer with your houses heating system or buy a little space heater for your tent off amazon or local for 40$.

Are all your fans on low?

I’m grabbing a space heater, humidifier, dehumidifier, a rh and temp controller (250 cnd ) this is the first year I’m having such drops. I think it’s because of my floor in my new place.
 
Because my plants are somewhat small Im assuming they dont take up as much co2 as if they were bigger, so thats why I was wondering if 45 minutes is too long to supply with fresh air.

I have a space heater that I used to run on high with exhaust fan running 24/7 but it only brought temp up to 20c from 18c so I found that to be a bit counter productive and also considering the increase in my electricity bill for 1-2 degree didnt increase didnt make much sense to me.

I made a quick chart to utilize the heater and exhaust fan as efficient as possible so that both are never running at the same time. However with that said if 45 mins is too long for air exchange in the tent then I need to re-plan out my setup.
 
I have the Mars 5x5 with 4 small static fans, and 1 medium oscillating fan inside with a 16” carbon filter running on high.
I have 2 of the 3 floor vents opened 100% and have a small heater outside of the tent oscillating indirectly.
All run 24/7.
The only issue I have is low humidity even with a humidifier in the room. Being in Flower it’s not a big issue, Veg will be a different story I sure.
 
AdaminCO said:
I have the Mars 5x5 with 4 small static fans, and 1 medium oscillating fan inside with a 16” carbon filter running on high.
I have 2 of the 3 floor vents opened 100% and have a small heater outside of the tent oscillating indirectly.
All run 24/7.
The only issue I have is low humidity even with a humidifier in the room. Being in Flower it’s not a big issue, Veg will be a different story I sure.
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Because of my setup with my 3 plants at different stages, Im trying keep RH at around 40-50%....I have a humidifer in the tent as well but if my exhaust fan is running 24/7 it will mimic my basement humidity which is at 18% and thats just bad news for all
 
780grow said:
Because of my setup with my 3 plants at different stages, Im trying keep RH at around 40-50%....I have a humidifer in the tent as well but if my exhaust fan is running 24/7 it will mimic my basement humidity which is at 18% and thats just bad news for all
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Yeah mines low. Hanging around 30-40%. Basements a consistent 35%. It’s dry in CO.
 
780grow said:
I got a 6" fan in a 4x4 on low and that thing already sucks the tits out of the tent, can't imagine 16" in a 5x5! you must have quite the negative pressure in there?
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Yeah it sucks the tent in some for sure. I can adjust it to prevent it, but at night it pulls the warm air in from the heater so...
I liked my room better, but ended up pulling it down. Homeowners don’t want you to grow and they came for a visit. Decided to roll with a tent vs. building it again.
 
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