Please educate me on passive intake

"Do I necessarily need ducting to lead to the passive intake vent?" - No.

The reccommend set-up seems to be...Filter, fan, hood, exhaust.
If it's a cool-tube hood, then it should be in the loop to keep the heat down.

Your grow room (to prevent smell) must operate with negative pressure, meaning that it sucks air in.

Hope this helps

passive intake works ok but if u are using a HPS 400 600 1000 ................unless u keep that room in the temp range of 65 to 62 so the passive intake takes it in at that ...your temps are going to climb fast and high

as for the size of it what is the size of your exhust ............u need to double it for the size of your intake (so the fan motor is not stressing)..........so if u are running a 6 inch u need a 12 inch intake hole .......8 inches u need 16

like the guy said negitive pressure is the key to keeping smell in...............but passive intake is not the only choice .............u can build a active intake just under powered compared to the exhust CFM


here is something i made up for my tent..............(rough a 6 inch inline fan is 400 cfms the tent pulls out with carbon filter on i am thinking 360 cfm a 6 inch inline booster fan (metal blades) is 240 cfm with the filter box 210 cfms ............so it is 150 cfms off u see the tent concave from the negitive pressure )........the best part about the filter box is the ducting inside u leave just little so u can clip it under the fan that is blowing in the area so when it moves is spreads cool air into the plants (if u have Co2 this is good method of adding unless u make the halo system ) ............i always tell ppl to get the lvl 10 filter it is hospital grade filtering so the plants get clean air (removing smoke virus mold bunch of bad things )....filters last 90 days

and yes the way u listed to hook in a carbon filter is correct ........................u want to hang the filter at the very top lvl of your area so it removes the hottest air from the area................velcro onestrap is great shit for hanging (home depot/lowes)

Hugo Phurst said:

"Do I necessarily need ducting to lead to the passive intake vent?" - No.

The reccommend set-up seems to be...Filter, fan, hood, exhaust.
If it's a cool-tube hood, then it should be in the loop to keep the heat down.

Your grow room (to prevent smell) must operate with negative pressure, meaning that it sucks air in.

Hope this helps

Click to expand...

justugh said:

passive intake works ok but if u are using a HPS 400 600 1000 ................unless u keep that room in the temp range of 65 to 62 so the passive intake takes it in at that ...your temps are going to climb fast and high

as for the size of it what is the size of your exhust ............u need to double it for the size of your intake (so the fan motor is not stressing)..........so if u are running a 6 inch u need a 12 inch intake hole .......8 inches u need 16

like the guy said negitive pressure is the key to keeping smell in...............but passive intake is not the only choice .............u can build a active intake just under powered compared to the exhust CFM


here is something i made up for my tent..............(rough a 6 inch inline fan is 400 cfms the tent pulls out with carbon filter on i am thinking 360 cfm a 6 inch inline booster fan (metal blades) is 240 cfm with the filter box 210 cfms ............so it is 150 cfms off u see the tent concave from the negitive pressure )........the best part about the filter box is the ducting inside u leave just little so u can clip it under the fan that is blowing in the area so when it moves is spreads cool air into the plants (if u have Co2 this is good method of adding unless u make the halo system ) ............i always tell ppl to get the lvl 10 filter it is hospital grade filtering so the plants get clean air (removing smoke virus mold bunch of bad things )....filters last 90 days

and yes the way u listed to hook in a carbon filter is correct ........................u want to hang the filter at the very top lvl of your area so it removes the hottest air from the area................velcro onestrap is great shit for hanging (home depot/lowes)

Click to expand...

Thank you both! I am going to play around with it a little bit. I'm going to stick with passive intake for now. If the room gets hot I can try something different. I was mainly confused with the duct leading to the intake. Also, I'm really lucky there is a shelf at 6 ft. my fan will most likely sit on that.

What are your thoughts on ducting itself; would semi-rigid ducting be good since (I'm assuming) it creates less turbulence due to the lack of big ridges like the flexible ducting has? Since I am going to have such a short run, I figure it won't hurt to pay a little more to get semi-rigid, if it is better. I'll have probably less than 8 foot of ducting with passive intake.

Thanks again!

ducting is simple

semi ridge is crap do not mess with it u will have more issuse then u would if u used flexie


ducting is simple .....u want to stretch it out as much as u can and keep it lvl.......if u have to make bends and all make sure u stretch it out then place it in the coner so u get a good angle (think of the air like water u want it to flow smoothly so strait lvl if u have to go down or upwards gentle slope)

if u are worried about making the angles correctly u can by ducting junctions that will form a clean bend (if the bend is done wrong it slows the speed of the air down and u lose alot of power)


if heat is a issuse go ahead and get yourself insulted ducting (this will keep the heat trapped in the ducting as it is moved out of the area.......it will not heat up the outside intake so it is cooler and works more effective)

and as for your end point .............i would put some kind of vent on it so the air is deflected and spread out as it exits and not just a jet stream of air

Not looking to hijack...but just read something here that I wonder about...
I have a 6" Hurricane on the ceiling pulling directly through a carbon filter into 6" PVC with one 90 degree elbow out the room. I have a 6" intake on the floor (opposite the carbon filter)that I have an 6" inline fan connected to on the inside and the "Amish Redneck Filter Cooling box on the outside" (can cooler with hepa filter). That said, I have been generally running with the intake fan not turned on for a couple reasons...but mainly because it seems to be running even when its not. My room is pretty airtight so the Hurricane pressure out is actually pulling what seems to be a reasonable amount of air in. (Plants seem ok, room has a little smell but nothing outside it). Actually kind of fun that I can hook a speed controller to just the Hurricane and seemingly control the speed on both fans. So bottom line is, Justugh, are you telling me that my intake is probably not enough and that I should really have that intake fan turned on high and/or something in addition?? Am I making my Hurricane work too hard...is that possible?

bravedave said:

Not looking to hijack...but just read something here that I wonder about...
I have a 6" Hurricane on the ceiling pulling directly through a carbon filter into 6" PVC with one 90 degree elbow out the room. I have a 6" intake on the floor (opposite the carbon filter)that I have an 6" inline fan connected to on the inside and the "Amish Redneck Filter Cooling box on the outside" (can cooler with hepa filter). That said, I have been generally running with the intake fan not turned on for a couple reasons...but mainly because it seems to be running even when its not. My room is pretty airtight so the Hurricane pressure out is actually pulling what seems to be a reasonable amount of air in. (Plants seem ok, room has a little smell but nothing outside it). Actually kind of fun that I can hook a speed controller to just the Hurricane and seemingly control the speed on both fans. So bottom line is, Justugh, are you telling me that my intake is probably not enough and that I should really have that intake fan turned on high and/or something in addition?? Am I making my Hurricane work too hard...is that possible?

Click to expand...

my filter box can work just on passive intake ......... if u have a fan in there now and it sucking hard making the little 6 inch spin u are doing damage to the 6 inch

the only 2 reason reason to add more air once u get to a good point is if u are adding Co2 or Heat issuses

the varible speed controller u use to get near the same speed as the smaller unit then just increase it a slight bit to keep the neg pressure this will get u the longest possible life out of both fans

the reason u can do that is the PVC it is keeping the CFMs in the upper range .......if u used normal ducting it would slow it..........i personally use a cross air system

here is mine
4x4 veggie as a fliter box .......210cfm rough guess running poss preasure on this one the hot air has 2 paths one that goes into my flowering tent and a 2nd one that dump out infront of the AC intake vent

the 5x5 glowering tent has a filter box and a vent coming from the veggie tent ......it is getting extracted by a 6 inch 400 cfm fan ..........it runs neg pressure................currentlly i do not have the carbon filter on when it is the thing needs to be att full power and i am just below equal pressure

currently my system the veggie tent air is dumped/exchanged once every 30 secs and the flowering tent some where once every 15/17 secs
buckets by the intake are mash buckets making 2 more gallons of shine..............the bucket on the table is my water bucket with the airstone

last of pics

Thanks...of course it is a bit difficult to figure my room air replacement value exactly or for that matter my positive or negative pressure as I am not in a tent. Not sure you ever saw my set up...I don't remember you commenting. But I would appreciate your input. I have the description and pics of my build here:

https://www.rollitup.org/t/thoughts-on-room.836894

No you don't need to run an intake duct but your tent may benefit from the lower outside temperature.

As for fans, just make sure the exhaust is always more powerful than the intake so you have negative pressure sucking the air in through the cracks.

Northern Lights Grower said:

No you don't need to run an intake duct but your tent may benefit from the lower outside temperature.

As for fans, just make sure the exhaust is always more powerful than the intake so you have negative pressure sucking the air in through the cracks.

Click to expand...

The only crack I have IS my intake fan. Seriously.

bravedave said:

The only crack I have IS my intake fan. Seriously.

Click to expand...

No grow room is 100% air tight.

Northern Lights Grower said:

No grow room is 100% air tight.

Click to expand...

You are probably right...and I knew you were actually responding to the OP.

bravedave said:

Thanks...of course it is a bit difficult to figure my room air replacement value exactly or for that matter my positive or negative pressure as I am not in a tent. Not sure you ever saw my set up...I don't remember you commenting. But I would appreciate your input. I have the description and pics of my build here:

https://www.rollitup.org/t/thoughts-on-room.836894

Click to expand...

by the way it is simple to figure out the refresh rate
u need to know the CF of the room .......what CFM does your fan run

then just some simple lowering for length of ducting number of bends and if u have a filter or not

filters i minus 10 to 15%
90 degree bends take off 3 to 5% .....if totally fucked up bend take 10% u know S shapes
length over 5 feet take off every 2 feet after 5 1% (so 7 feet 1% 9 feet 2% 11 feet 3% and so on)

this is all just rough math in my head from playing around with the booster and varible speed controler ............someone wants to give me 100o bucks for the tools i will measure and pass the figures out u can have the tools back once i get it (was that important to me)

you would be better off using two fans to remove air, with a passive intake
if you were considering using two fans anyway

one fan used to blow air through the light/s hood etc if you use cool tubes
this air will run through the light system and out of the grow space it will not need a filter as this air will not mix with the air in the grow space,
you can blow cold air from outside or low down through the lights this will generate positive pressure in the lighting system
this fan will remove much of the heat

the second fan can extract the air from the space to pull in fresh air from the passive inlet
this will create negative pressure and help to control the smell this fan will need a carbon filter

Thanks, yeah I know I can do some rough figuring, but right now I am just reading the room and it is telling me that it is happy. Winter is going to bring some challenges...and possibly the next month too as I really have been weather lucky and next week will bring the summers hottest temps. Glad my lights are now off during the day.

justugh said:

ducting is simple

semi ridge is crap do not mess with it u will have more issuse then u would if u used flexie


ducting is simple .....u want to stretch it out as much as u can and keep it lvl.......if u have to make bends and all make sure u stretch it out then place it in the coner so u get a good angle (think of the air like water u want it to flow smoothly so strait lvl if u have to go down or upwards gentle slope)

if u are worried about making the angles correctly u can by ducting junctions that will form a clean bend (if the bend is done wrong it slows the speed of the air down and u lose alot of power)


if heat is a issuse go ahead and get yourself insulted ducting (this will keep the heat trapped in the ducting as it is moved out of the area.......it will not heat up the outside intake so it is cooler and works more effective)

and as for your end point .............i would put some kind of vent on it so the air is deflected and spread out as it exits and not just a jet stream of air

Click to expand...

I think I may try insulated ducting. Everyone says you have to make a larger exhaust hole. I was wondering, can you just cut some of the insulation off to fit the 6" duct in the hole, or should I just use a bigger hole?

bravedave said:

Not looking to hijack...but just read something here that I wonder about...
I have a 6" Hurricane on the ceiling pulling directly through a carbon filter into 6" PVC with one 90 degree elbow out the room. I have a 6" intake on the floor (opposite the carbon filter)that I have an 6" inline fan connected to on the inside and the "Amish Redneck Filter Cooling box on the outside" (can cooler with hepa filter). That said, I have been generally running with the intake fan not turned on for a couple reasons...but mainly because it seems to be running even when its not. My room is pretty airtight so the Hurricane pressure out is actually pulling what seems to be a reasonable amount of air in. (Plants seem ok, room has a little smell but nothing outside it). Actually kind of fun that I can hook a speed controller to just the Hurricane and seemingly control the speed on both fans. So bottom line is, Justugh, are you telling me that my intake is probably not enough and that I should really have that intake fan turned on high and/or something in addition?? Am I making my Hurricane work too hard...is that possible?

Click to expand...

lol That's okay, at least what you're talking about pertains to the subject. So I learned something from it ^_^

Also, idk why I can't like things, maybe it's because I'm on safari, that is not an option for newbies, or it just isn't available right now. But I love to like things, and I wish I could like your all's stuff haha.

skunkd0c said:

you would be better off using two fans to remove air, with a passive intake
if you were considering using two fans anyway

one fan used to blow air through the light/s hood etc if you use cool tubes
this air will run through the light system and out of the grow space it will not need a filter as this air will not mix with the air in the grow space,
you can blow cold air from outside or low down through the lights this will generate positive pressure in the lighting system
this fan will remove much of the heat

the second fan can extract the air from the space to pull in fresh air from the passive inlet
this will create negative pressure and help to control the smell this fan will need a carbon filter

Click to expand...

I was considering having a circulation fan by the passive intake and angling up so it wouldn't hit the plants straight on. Would this be kinda what you're talking about, or do you mean two fans and a circulating fan?

insulated

it works a little different ................u attach the ducting (not the insulation yet) to the points they need to go and hose clamp it down then u take a zip tie on the outside of the insulation and close it down around the clamp


your ejection point is the same thing u attach the ducting then zip tie it down ................the ducting itself is nothing but wire and plastic the insulation is the fiberglass and mylar .................i personally would not strip off any insulation because the sec u do that heat will excape from that section along with the ejection

it really helped me ................with it on it keeps the room 7 to 10 degrees cooler then then it was just flexie

make sure u usea end vent point so the air is deflected ...........it will help keep u hidden along with keep bugs from going in .............
http://www.amazon.com/Dundas-Jafine-SEVZW-Soffit-Exhaust/dp/B002BHVWCA

the one i own................i spray painted mine black and used a peice of plywood.........cut a hole attached the vent then put it in the window and attached the ducting to the back ................if u have a AC just push it to one side

i mean you use a separate fan for the removal of heat and the removal of stale air normally folk would use one extractor fan to do both jobs at the same time , the extractor fan sucks the heat out of the room and lights at the same time and brings in new air rich in co2 for the plants through the passive inlet

but you can use two extractor fans , one of them will suck the stale air out of the room and bring in new co2 rich cool air
from your passive inlet, this will cause negative pressure in the grow space this fan will need
a carbon filter this fan and filter can be mounted above your lights somewhere high

the second extractor fan will be used to BLOW air, the reason for blowing is so this fan does not need a carbon filter, the air you blow through the lights will never mix with the air in the grow room
the air from this fan will flow though the cool tube across the light and out of the ducting vented out of the grow area
the positive air pressure in the light system caused by blowing will prevent smelly air from the grow space entering the light system so no smell will come out of this ducting
also the hot air will not flow through the fan motor itself which is better for the fan as you are not sucking the heat out of the lights you are blowing cold air through them
you can suck air from an outside window if its cold outside and blow it though the lights
you could use a portable air conditioner instead of the extractor fan to blow very cold air through the lights you can attach some ducting yourself onto the front of an air conditioner
this carry's the heat from the lights away with the air stream before it can heat up the air in the grow space too much

its better to try to remove the heat at source before it gets a chance to heat up the space
rather than letting the light heat up the air, then trying to remove this air very quickly with a extractor
its almost always a losing battle the light wins in a small space

using a powerful floor fan that blows a powerful stream of air at the lights as an alternative
will also cool them down a great deal and reduce the temperature at the canopy level
it will also make them swing/move around a fair bit
this hot air must still be sucked out of the space by your extractor though so its only moving
the air somewhere else in the room away from the plants it helps but it must still be
totally removed or over time heat builds up
so overall it is much better to do it with cool tubes. and ducting