negative pressure in tent

griggzzzy · Aug 3, 2017

hi all i just changedy outlet on my tent to a 6 inch with much larger carbon filter to get ready extract more heat when i put the 2x600w hps in for flowering as tent was sittinf mid 70s with a 300w and 250w cfl but my inlet is only a 5 inch . my tent used to look slightly inflated but now its looking sucked in will this cause me problems if so ill just add a 6 inch inlet i was worried id be sucking out more than coming in and could starve the plants
any help would be great ...... thanks

Mobileaudio25 · Aug 3, 2017

Are you running a passive intake?
Make your intake bigger or add more holes. That will reduce the negative pressure and help with lowering temperatures. You want the walls sucking in some but not too much.

You won't starve the plants In terms of CO2. in order to get negative pressure you have to suck out more than you are bringing in.
Normally intake needs to be 2-3 times the size of your exhaust

Rusher · Aug 3, 2017

When the sides of your tent suck in slightly, that's a good thing. Fan/filter doing it's job correctly.

griggzzzy · Aug 3, 2017

Mobileaudio25 said:
Are you running a passive intake?
Make your intake bigger or add more holes. That will reduce the negative pressure and help with lowering temperatures. You want the walls sucking in some but not too much.

You won't starve the plants In terms of CO2. in order to get negative pressure you have to suck out more than you are bringing in.
Normally intake needs to be 2-3 times the size of your exhaust

yeah i was thinking after upping the exhaust i think il go with the two 5 inch ones bringing fresh air in and the 6 inch taking it out . im adding the cool tube hps fittings in a few weeks when i switch to 12/12 so hopefully that will keep the temp nice with the hotter lights

ilovetoskiatalta · Aug 8, 2017

I run my fans on a variac and have an active intake fan. The air flow in keeps the tent from sucking in. My tents are small so I don't want them sucking in on the flower tent.
The little tent has a 4x12 phresh filter on a hurricane 171cfm on a variac that pushes air into a 4x2 with a mountain air 4x16 also on a 171cfm hurricane on a variac. I think the variac is well worth the money.

The little tent is a drying/cloning tent that has a 2' x 2' 8 bulb t5 that is not always on.
the 4' x 2' is my flower with a 315cmh

You can see the little tent is sucked in but the flower tent does not thus does not crowd my flowersView attachment 3991970 View attachment 3991971

coreywebster · Aug 8, 2017

griggzzzy said:
yeah i was thinking after upping the exhaust i think il go with the two 5 inch ones bringing fresh air in and the 6 inch taking it out . im adding the cool tube hps fittings in a few weeks when i switch to 12/12 so hopefully that will keep the temp nice with the hotter lights

You have to take into account that your 6" fan is reduced in power by adding the filter and ducting and any bends.
If you have 2x 5" intake fans you will have to much intake and result in positive pressure pushing stink out of your tent.
Not sure what the guy above you is talking about, intake been 2 or 3 times the exhaust, unless he means that as a rule for passive intake.
Just open all your vents for intake or add passive ducts. No need for intake fans with a 6" exhaust. A separate fan on the cooltubes would help but its not a must either.

Your intake if you do use one should be smaller than outtake, you want negative pressure, variable transformers are a good option to ensure you have negative pressure without too much.

griggzzzy · Aug 9, 2017

coreywebster said:
You have to take into account that your 6" fan is reduced in power by adding the filter and ducting and any bends.
If you have 2x 5" intake fans you will have to much intake and result in positive pressure pushing stink out of your tent.
Not sure what the guy above you is talking about, intake been 2 or 3 times the exhaust, unless he means that as a rule for passive intake.
Just open all your vents for intake or add passive ducts. No need for intake fans with a 6" exhaust. A separate fan on the cooltubes would help but its not a must either.

Your intake if you do use one should be smaller than outtake, you want negative pressure, variable transformers are a good option to ensure you have negative pressure without too much.

thanks for the info ive stuck with the 1 x 5 inch intake and the 1 x 6inch exhaust through the carbon filter . makes total sense what you say about positive pressure pushing out the smell . after reading this negative seems the right way to go . i will be adding 2 cooltube light fittings soon i was gona set ut up so i had it like this ......
Carbon filter - 1length of tubing allowing lights to be moved then cool tube light then small bit of tubing then cool tube light then more tubing to fan allowing light adjustment then from fan tubing out of tent and away . will this be ok sucking the hot air through the fan like this or would pushing the hot air out be better ? i wasnt sure if the fiter would work right being blown through positioned outside of then insted of sucked through positiined inside

disbeverk · Aug 9, 2017

You want negative pressure in the tent. Passive intake and sucked in walls is ideal.

disbeverk · Aug 9, 2017

You want to suck in through your filter. If you had the room in your tent you should go Carbon filter -> Cooltube -> fan -> exhaust.

coreywebster · Aug 9, 2017

I used to run mine.. Filter>fan>cooltube>cooltube>cooltube ducted to chimney. For the reason you said, because my fan is the most expensive part of my set up (or was) I didn't want all that heat going through my fan. Some say it can dry out the bearings faster. I see lots of people running as disbeverk says and I have not heard anyone saying the fan failed so I guess both ways work.
BTW I found a good connection duct for between cooltubes was 6" dryer vent, which is flexible, thin and can be pulled tight so there are less ridges and less turbulence for the air flow. Its not light proof but that doesn't matter as long as you only use it with the tent, I had it between cooltubes and from fan to first tube. after the last cooltube its normal acoustic ducting going into chimney.

griggzzzy · Aug 9, 2017

disbeverk said:
You want to suck in through your filter. If you had the room in your tent you should go Carbon filter -> Cooltube -> fan -> exhaust.

cool thanks its just coz i read so many conflicting things id read it will ruin the fan because of the heat but my thinking was its there to extract heat so should be upto the job

griggzzzy · Aug 9, 2017

coreywebster said:
I used to run mine.. Filter>fan>cooltube>cooltube>cooltube ducted to chimney. For the reason you said, because my fan is the most expensive part of my set up (or was) I didn't want all that heat going through my fan. Some say it can dry out the bearings faster. I see lots of people running as disbeverk says and I have not heard anyone saying the fan failed so I guess both ways work.
BTW I found a good connection duct for between cooltubes was 6" dryer vent, which is flexible, thin and can be pulled tight so there are less ridges and less turbulence for the air flow. Its not light proof but that doesn't matter as long as you only use it with the tent, I had it between cooltubes and from fan to first tube. after the last cooltube its normal acoustic ducting going into chimney.

thanks for all the info i can see plus sides in both ways i got 2 spare fans if one packs up just didnt wana do somthing that couldve been avoided with a simple question

disbeverk · Aug 9, 2017

griggzzzy said:
cool thanks its just coz i read so many conflicting things id read it will ruin the fan because of the heat but my thinking was its there to extract heat so should be upto the job

Nothing wrong with having the fan front in front of the heat and pushing through the tubes. Just want to be sucking through the carbon filter, and out of the room, creating negative pressure.

negative pressure in tent

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