Is Passive intake enough

J

Jennylasting

Active Member
Hello all!

some questions about passive air intake and my airflow issues, the weather here is hot...real hot, 25/7C sometimes outside or in, without my new 4" fan it somehow stayed at around 30C which is too high for my plants i know. I only bought one fan though, needing a 0.1A fuse i aint installed it yet! my tent is 3.8 cubic metres and my fan moves around 107/m3 and hour, as i have no A/C though (Too Expensive), the air being pulled in is practially too hot for my plants and is passive, is this enough airflow and is it really going to cool the tent down much?, the doors are open now, really i want them closed to get maximum light but it's so damn hot!!!!

any help would be sweet?

*supporting tim and eric awesome show great job!*
 
mr2shim

mr2shim

Well-Known Member
Create negative pressure within your tent. Will increase efficiency a bit and help with the temps.
 
J

Jennylasting

Active Member
yo! thanks for the advice, just a teensy bit more information?

so i should create a smaller are of air intake? should i also only use a 0.1A fuse for my fan? or can i get away with higher, I have 0.5A glass fuses and some 3A regular fuses
 
mr2shim

mr2shim

Well-Known Member
IMO use w/e fuse the can came with. Having more A isn't always a good thing when it comes to fuses. With the negative pressure bit what I do is, I run my setup in this order.. Filter, Light, Exhaust fan. With the fan sucking air through the filter then cooling the light and out the tent. Doing it that way I eliminate the need for an intake fan. Also, seal up all the seams because the fan will suck air from every hole in the tent. I have a 4" intake at the bottom sucking in cold air and the hot exhaust air exits out the top of the tent.
 
F

F A B

New Member
use the fuse it is rated for going larger decreases your fans protection and is not safe
and will not increase fan speed

so dont do it
 
graab187

graab187

Active Member
i have my exhaust at the top of my closet sucking air into the attic. my closet is all sealed and air tight so it creates a negative pressure at whichever hole is open in my tarp stapled around my closet opening. si i put a little 4'' leftover ducting i had and put it at the bottom and sealed it all up. i turned my fan on and watched the negative pressure PULL in freshh fresh air from my room into the closet just from the power from the exhaust.

i could hold a tissue paper at the ducting and it would be sucked into my closet it was so strong!
but is this enough? i feel like im PULLING more air out of the closet with my exhaust than im pulling air in for the plants to grab the co2.

maybe i could make another passive intake at the other side of my closet to also add some fresh air

thanks RIU
 
dimebag87

dimebag87

Well-Known Member
Put it this way I live in the uk and it's winter. I have a 400 watt hps in a 1.2 x 1.2 metre tent with a 4 inch exhaust, 4 inch intake, and two six inch clip on fans in there. It still gets hot! It's acceptable for winter but as soon as summer kicks in It'll be a cool tube with a six inch exhaust and a 4 inch intake.
 
SFguy

SFguy

Well-Known Member
graab187 said:
i have my exhaust at the top of my closet sucking air into the attic. my closet is all sealed and air tight so it creates a negative pressure at whichever hole is open in my tarp stapled around my closet opening. si i put a little 4'' leftover ducting i had and put it at the bottom and sealed it all up. i turned my fan on and watched the negative pressure PULL in freshh fresh air from my room into the closet just from the power from the exhaust.

i could hold a tissue paper at the ducting and it would be sucked into my closet it was so strong!
but is this enough? i feel like im PULLING more air out of the closet with my exhaust than im pulling air in for the plants to grab the co2.

maybe i could make another passive intake at the other side of my closet to also add some fresh air

thanks RIU
Click to expand...
youll be fine, i dont even vent my 400 watt light in a 2x4 foot veg tent, AND passive air also works for me in my 9x9 2200watt flower room too, 5-600cfm out and passive in all the way. running a 1000watt light and 2x600's and a 8000btu portable ac unit.


dont overthink it man


and FYI my veg tent does hit mid 80's and lows around 65. i do also have a fan blowing around in there too small like maybe 8inches

id likely have to exaust during the summer but i have only been running the tent to veg in since august so ill find out more this summer. i was vegging in the room then flipping to 12/12, but now im just running a perpetual cycle taking clones every month.
 
glockdoc

glockdoc

Well-Known Member
there is a chart on how to keep x amount of watts within 5-30 degrees of ambient telling u x amount of cfm. there's a formula for this. off the head i know to keep a 400 running at 10 degrees difference from ambient in grow room u need 100-110 cfm. so if room is 70 ur grow cab will only be at 80. this is sealed hood with glass it holds true to
 
legallyflying

legallyflying

Well-Known Member
passive intakes need to be sized 4x larger than your powered outlet.

I doubt that a passive intake is going to be enough.

What fans come with a fuse anyways?
 
graab187

graab187

Active Member
SFguy said:
youll be fine, i dont even vent my 400 watt light in a 2x4 foot veg tent, AND passive air also works for me in my 9x9 2200watt flower room too, 5-600cfm out and passive in all the way. running a 1000watt light and 2x600's and a 8000btu portable ac unit.


dont overthink it man


and FYI my veg tent does hit mid 80's and lows around 65. i do also have a fan blowing around in there too small like maybe 8inches

id likely have to exaust during the summer but i have only been running the tent to veg in since august so ill find out more this summer. i was vegging in the room then flipping to 12/12, but now im just running a perpetual cycle taking clones every month.
Click to expand...

Yeah I was basically just worried about my temps being too high. I was wondering if I should just spend the extra money on a completely sealed hood and connect my exhaust to it? Would this drop my temps a significant amount? Because right now I just have my exhaust in the attic with ducting hanging down under the light sucking the air. If I got a aircooled hood would it eliminate my passive intake I have going?

I'm just worried my plants aren't getting enough co2 in the air because my exhaust is so powerful and my intake is so small. My closet is always sealed with my exhaust set on a timer to go on every 2 hours for 30 minutes to exchange the air. Should I add another small passive intake? Or do you think my plants are getting enough co2. I think I'm just being paranoid. I just want my girls to explode when I flip them to flower
 
jrainman

jrainman

Active Member
example 4ftx4ft = 16 sq ft x8ft ceiling = 128 cubic ft now you have a 400cfm fan ( cubic ft per min) so divide your cubic ft 128 by your fan CFM cubic ft per min = how many times per min you can exchange that air in that particular area. As for intake Passive size this is done by how many sq inches of air can pass through a certain area (duct) a ductulator will give you the correct sizing but for the most part always size at least the next size up a 6inch round duct will handle up to a 120cfm a 8inch round will move 200 cfm and a 10 inch round will move 500 cfm 12inch round 900cfm 14 inch round 1200 cfm.
 
SFguy

SFguy

Well-Known Member
huh??^^^


i use a 6" 500 cfm blower to exaust my room and lights my entire 2200 watt 9x9 room has passive intake from that blower causing back pressure. i run it all thru 6" inch ducting temps hit max 88 and regularly are around 79-82
i run my lights at night if that makes a diffrence to anyone, cause its too hot to run em during the day, and its off peak hours so i get a better rate + im on the c.a.r.e program for low income families and that gets my rate down to 12.c per kwh
 
jrainman

jrainman

Active Member
Again if you do not have the surfice sq inches of inlet (opening from your fresh air space) you are not running true passive( Neg )bottom line is you spent real good money on a good quality exhaust fan and your not letting work on the full potential it can ,everthing has to work together to achieve the full potential. so bottom line if you have more the a 5 deg dif in temp from your fresh air supply to your room your not sized correctly. 2 deg diff is what can be obtained or better.
 
glockdoc

glockdoc

Well-Known Member
legallyflying said:
passive intakes need to be sized 4x larger than your powered outlet.

I doubt that a passive intake is going to be enough.

What fans come with a fuse anyways?
Click to expand...
aint it 2x..which is rule of thumb.... cant say you are wrong with the 4x simply because they do say the more passive u add after that 2x the cooler ur cab/grow area will be.
 
SFguy

SFguy

Well-Known Member
jrainman said:
Again if you do not have the surfice sq inches of inlet (opening from your fresh air space) you are not running true passive( Neg )bottom line is you spent real good money on a good quality exhaust fan and your not letting work on the full potential it can ,everthing has to work together to achieve the full potential. so bottom line if you have more the a 5 deg dif in temp from your fresh air supply to your room your not sized correctly. 2 deg diff is what can be obtained or better.
Click to expand...
i have to run an a/c unit too.. i guess i should buy a bigger fan then to cool my 1000 wat light and 2x600's then. i guess its not truly a passive intake as you say cause the size of my openings.. but by DEFINITION I AM RUNNING A PASSIVE INTAKE CAUSE I HAVE NO FORCED AIR COMING INTO MY GROW ROOM.. its all comes in how??? say it with me.. pas-siv-ly
 
glockdoc

glockdoc

Well-Known Member
no forced air is indeed passive true that. only up to a certain point were the whole u create will leak air if u have exhaust only. air will only get sucked in. with a fan u can push more air in then u do out which will make it leak thru cracks and what not..not neg pressure
 
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