Tutorial Ventilation 101

[menoseloso]

Hi Red,

This is an invaluable thread. I remember reading something similar to it on OG a few years back. I'm trying to plan out my exhaust system for a future grow and would like some advice if you have the time.

I used to use a 4" vortex fan in a small closet grow with a 400w hps. I had it set up pretty well and kept the temps at a good level. Only problem was that the fan and the sound of the rushing air were far too obvious. This time, I would like to go for a much stealthier set up. I will be building a false wall to enclose a 8 foot by 4 foot grow room. On one side I will have a 3x4ft flowering room with 600 watts. I'm going to run an air cooled hood straight into the next room or into the attic. I have seen a lot of references to the S&P TD series fans. I understand the more static pressure, the lower the performance of the fan, but stealthiness is of the utmost importance. The lower power usage is nice as well.

What I am thinking is that I would use the 8" S&P TD-200 rated at 538cfm to cool my hood. It's going for the same price as the S&P PV-150x, which would be other option, and it would be a bit quieter. If I had a straight run from intake, through the hood, and out the exhaust, do you think this fan would maintain adequate temperatures? I would certainly use a smaller fan to do a proper air exchange in the flower room. I would like to keep the temps within about 5-8 degrees of ambient.

One other question, if I did go with the 8" fan and I decided to use a hood with 6" flanges, could I insert the six inch duct into an 8" duct running to the fan to cool the light and act as an exhaust for the room as well? The problem I'm running into is that buying an 8" cool hood is significantly increasing the cost of choosing this fan. Would drawing from a six inch air cooled hood while drawing from a 2 inch gap around the duct increase the static pressure to the point that the benefits of this fan are decreased?

I guess what I'm asking is what would you do?

Thanks for any input and I'm sorry about the long post!!

 

[flfunk]

Okay, I want to pre-apologize if this has already been touched on in this thread (which i am sure it has been). But, I am at work doing this and i have only gotten through the first few pages and now they actually want me to do work...

Anywho, I am running a 600 watt vented hood right now. It is my first grow and right now it is what i would call a high school setup. My room is unused so it is just the light in the closet (6' x 2' x 8' folding door closet) with fans and what not, doors open. My temps are fine right now, but i want to close the closet up ASAP. So i have ordered my panda film and determined i am going to go with the 3rd description in the first post (simple cab with vented hood and inline scrubber) and have my vent go into the attic. Now i just need to order the inline fan and scrubber. I have tried to figure this out on my own real quick, but I am still a bit confused about what size fan i need.

Will a 4 inch inline fan with carbon scrubber that pushes 190cfm be enough? Or do i need to step it up to a 6 inch, that pushes 440 cfm? I know i have 96 cubic feet in the closet so in theory the 4 inch will be more than enough, but i couldnt understand the calculations and language that was being used while reading over it quickly. I am going to try and figure this out on my own, but any help would be appreciated.

oh and the intake will be 2 4 or 6 inch vents coming from two seperate rooms.

 

[ITryToGrow]

I'd go with the 6" fan. The 4" fan will be noisy as hell, the 6" you can put on a speed controller and turn it down.

 

[FlyinHawaiian]

I have another question now, does anyone know the sq " intake area of an 8x8 darkroom louver? I think I remember reading these vents block 1/2 the air flow? is that true?, so that equals a 4''square hole, so 16sq'' of intake a good guess? thats not much[/QUOTE] bump

 

[Geoffrey Boycot]

Awesome awesome thread. great job contributers.

As i understand it this will allow me to buy less [expensive] fans than i expected too. I'm new to this, so please bear with me...atm i have rigged up 8" desk fans to blow air thru some ducting and away from my lights. its crap. trying to get better.

I plan to build a 9'x3'x6' grow area inside a spare bedroom (11'x8'x10'?) with, atm, 2x600w air cooled lights with 6" vents. The ducting will hopefully vent into the attic space. approx 5ft away (as the crow flies) from the end of the grow area. I don't have a need to scrub as far as I can tell...

So....

Grow area: 162 cu ft
CFM req'd to vent lights to +30F: 126.4 (3.16*1200/30)
CFM req'd to vent grow area: 32.4 (162/5)
Friction loss to ducting: 0.21" per 100ft (160cfm / 6" duct)

I was hoping to use the $27 home depot axial fans as they are rated for 160cfm and using that maths appear to do the business for what i require, though i'm sure i'm missing something to do with pressure. Red seems to rate them more like 75 cfm though which is worrying.

I only have 10ft of straight ducting to deal with, 2 bulbs to get past, and then a curved bend up to attic for about 5ft in order to vent the lights.

Would it be best to have a 6" duct intake start outside the grow area (inside the bedroom 'lung') that moves air thru the lights, thru the $27 axial fan and into the attic. And then find some other way of venting the grow area somehow eg would a 20" floor fan placed next to a lifed flap of panda sheet allow the req'd 30CFM for room venting? Or do i need seperate ducting + another $27 axial? (+muffler to prevent excessive grow room ventilation?)

Or would it be best to vent both the lights and grow room at once by having the intake duct for the light-cooling within the grow area itself thus eliminating the need for extra ductings/fans. Or does that mean the fans are going to attempt to recycle my room air approx once a minute?

In summer temps can be 80-85F - is a 110F duct exhaust into the attic space really going to cut the mustard in terms of getting my grow area 75-90F?

What kind of axial fan can deal with this kind of venting requirement if not a home depot one? Or do i need to go inline/centrifugal? If i ever want to expand the lights to 3x600w in the same area do i need to bite the bullet now and get the inlines?

Thanks for any help, its been a fascinating 3-4hr read. please excuse the garbled nature of my enquiries. its late and and i may be, erm, 'tired'.

Geoff


ps my bedroom 'lung' also has approx 600w of vegging energy in it and the ability to open a window to outside and a door to rest of house.

 

[hoosierdaddy]

I use a single duct booster for cooling my lights, right in and right out of the cab.
Duct boosters are just that...boosters, and not much of a boost at that. They are nifty little fans, don't get me wrong...but for exhausting the room, you need something that can pull harder. The duct boosters can get up to maybe 150CFM with zero restriction, but the second they meet any resistance at all, they start to drop off like a rock.
A better choice for the frugal would be to DIY a Stanley(Lasko) fan. These 3 speed blowers do a great job using 6" ducting.

 

[Geoffrey Boycot]

I use a single duct booster for cooling my lights, right in and right out of the cab.
Duct boosters are just that...boosters, and not much of a boost at that. They are nifty little fans, don't get me wrong...but for exhausting the room, you need something that can pull harder. The duct boosters can get up to maybe 150CFM with zero restriction, but the second they meet any resistance at all, they start to drop off like a rock.
A better choice for the frugal would be to DIY a Stanley(Lasko) fan. These 3 speed blowers do a great job using 6" ducting.

Thanks for the reply...There's a couple of things i'd like to clarify if you dont mind?

From my calc. i only need 30-40cfm to clear my room once every 5mins? Why do I need a more powerful fan to clear the room than to clear your/my lights? You use an axial to vent your (550w?) lights, but dont think i could use them to vent 1200w?

The only 'restrictions' i have are 2 bulbs/hoods, and 15ft of nearly straight flexi-ducting...this is still too much?

The fan you recommend, i think, puts out 1300CFM on its lowest setting?!

So place that at the start of the chain (maybe at ground level to collect cooler air?): Lasko fan->5ft ducting into grow area->two lights and 10ft of ducting in grow area->5ft ducting outside grow area->attic space. Plus maybe 1 axial/floor standing fan to vent the grow area itself?

thanks again
Geoff

 

[booghy]

Well no replies to any of my questions yet, but I'm hoping to get

one now. I'm setting up my cab 2mor so hopefully my plans are ok.

Cab is 48" W x 20" D x 72" H. I plan on using about 30" of that

width for my flowering chamber. I have 2 S&P TD 100x fans. One

will be used to pull through a 4 x 8" Phresh filter, the other used to

cool the light in a cool tube. I also have a 6" booster fan I could

use to help out either fan, or primarily for cooling the cooltube if it

will be enough, allowing me to use the other S&P for my veg side. I

was planning on buying 2 8" darkroom louvers for my intake. My

fan is rated at 135 cfm, but the phresh filter is rated for 150. Will

this cause an issue?? Also do you guys think 2 8" louvers are

adequate?? I know they restrict airflow pretty bad so if it's not

enough, would going with a single 12x24" louver be better?? Any

help or replies are appreciated as I'm not much of a handy man and

have someone helping me build those who will only be in town

tomorrow.

 

[sneakinman13]

top for help!?!

well i ended up gettin it worked out!
just needed to add 2 passive intakes.... went with 12 inch passive intakes on top of my active 6 inch intake for room. not to mention the fans cooling my lights...

only thing i think that could improve my setup up is stronger fans for the lights. maybe a 12 and a 10 instead of 10 an 8. but with the use of my AC im keeping my temps in check!

thanks for the help ppl...

later

 

[weeeduh]

awesome thread, these are EXACTLY the specs I need to build out my first cabinet. I appreciate the technical details very much.

If some techie will take a look at my design pictures, I'd like to know some ideas for venting this out. I think I pretty much have the heat taken care of, I am just a little stuck on how to vent and scrub the main chambers.

Right now I am only concerned really with getting the main chamber vented and scrubbed, but I'd like some ideas on getting air flowing through this entire cab.

Thanks for any feed back. No rush or anything, I still have a lot of design to work out. Everything is to scale, and those are 6" ducts in the light.

I need to be very stealthy so keeping the aroma down as well as running silent as possible is key.

Dimensions in the picture.

 

[Greensci]

Hi. Red. Thanks for the informative thread. I've read through it a couple times but I can't seem to find the answer to my question. I was wondering if I could use one exhaust fan with a Y connector to exhaust both my air cooled hood (with outside air) and the carbon filtered air from the growbox separately. Would one part work properly and not the other because of the air coming from path of least resistance? I'm sure it's here somewhere and I've missed it so feel free to just link me back to it.

Much appreciation for all the hard work and diligence that has gone into this thread!

 

[ITryToGrow]

Hi. Red. Thanks for the informative thread. I've read through it a couple times but I can't seem to find the answer to my question. I was wondering if I could use one exhaust fan with a Y connector to exhaust both my air cooled hood (with outside air) and the carbon filtered air from the growbox separately. Would one part work properly and not the other because of the air coming from path of least resistance? I'm sure it's here somewhere and I've missed it so feel free to just link me back to it.

Much appreciation for all the hard work and diligence that has gone into this thread!

You can do that, but to ensure that both "ducts" get proper airflow you can used damper(s).

 

[J23]

Hi guys, newbie here. I must confess that the first time I came across this thread I thought it's too long, to much equations etc. Being ignorant I have almost purchased fan/scrubber that would be an overkill for a grow cab I'm building right now. Second time I saw this post I decided to give it a try. English is my second language so translating was a bit pain but I'm glad I've finished reading whole thing. Will do it probably once again 'cause so much useful info in here. Thanks to all of you guys! as I mentioned I'm struggling with choosing fan and scrubber and so far I gathered that for my 10cu ft box, 250w hps w/cooltube I need 25sq in passive intake for 4" cool tube exhaust, 40cfm axial fan for the cooltube. Since box is not running yet I assume delta T to be 20F (room temp at 72F). in one of the earlier threads (Red' Greenery's 150 HPS Cab, #53) Red suggested using scrubber of 2sq ft with a 1" thick bed of carbon for almost the same size grow box. I'd like to make sure that I got it right:

Are those numbers OK for a two stage cooling/venting setup or I need to read this thread a couple more times?

hoosierdaddy, DiscoBiscuit, muddywaters, PoisonedDart: thanks for your help!

 

[jaranth]

IMHO, the info in this thread is ESSENTIAL for cab builders. I've read through it a few times, and still have some things to work out...

For closet-sized and larger rooms, this ventilation stuff seems relatively easy to me. However, if one is trying to ventilate a VERY SMALL CABINET, things start getting a bit more confusing.

It was stated that more than 1 ACpM stresses the plants. Therefore, putting in a big fan/scrubber on a 5 minute timer would be a terribly inefficient solution.

SO -- Let's suppose you have a cab with a separate, ventilated light, so heat from it isn't a factor in trying to figure out ventilation for the cab.

Now, if the cab is really small... say 20 cu. ft... and one wishes to vent every 5 minutes, then (using the math in this thread) the cabinet would need only 4 CFM! The smaller PC fans are still around 30 CFM or so, therefore there has to be reduced air flow somewhere.

Of course, some of this will be across the scrubber... but is that the typical way cab builders do it? Rely on the scrubber to "adjust" the overall air flow created by a fan that is too fast?

Anyway, I can only think of the following ways to deal with this:

1) Scale down the scrubber (or add more carbon) so it creates more resistance to air flow (and match the speed necessary for the scrubber to work properly). However, if your fan is rated for normal operation at something like 5 times faster speed than what you need, wouldn't doing this heat the fan up, possibly causing failure, and maybe other problems such as heat? Maybe PC fans can take it, I dunno.

2) Reduce the size of the intake(s) to slow air flow. For this to work, the intake(s) would have to be smaller than the exhaust... bad idea, right? It would create extra work for the fan and be inefficient.

3) Slow the fan down using a speed control, and move to a bigger scrubber. At present, this makes the best sense to me.

I'm probably over-thinking this, or maybe it really is all over my head!

Regardless, I betcha there are still some small cab builders out there that are still confused, just like me. The math isn't the problem, it's HOW to scale down from the examples given by the pro's, but maintain fan efficiency. Help!

(Oh, and BTW: Hello ICmag!)

 

[gdbud]

I would not worry to much about trying to achieve 1 ACPM my option is that you need more than that and here is my reason and yes Redgreenry you my correct me if my line of thought is wrong.
I have a cabinet that is 22.5 sqft. and my air flow through the cab. is 85 cfm which is 3.75 air changes per hour and with two fans inside blowing air on the plants I was having problems with moisture collecting on the leaves. To solve the problem I add another fan now I have two fans blowing down on the canopy and one blowing under the canopy.
With that much air flow from the fans you would think it would stress the plants and everyone I know of has fans running in side their cabinets.
I'm running a DWC with a scrog and my two plants are consuming a gallon of water a day, So these plants must be putting out a lot of moisture.

 

[J23]

Can anybody advice on my setup on #353

 

[hoosierdaddy]

J23,
For the light, you can run a 4" duct in to the light and a 4" duct out to the fan. No need to oversize the intake for the light cooling duct. This air train doesn't need to be scrubbed as long as your light's glass is sealed up well.

You need a second air train for the room air. Mounting a scrubber up high if possible, through duct to a fan and exhaust. The intake on this needs to be the double sized passive intake and should be low in the grow area.

 

[Dignan]

Question that may or may not be answered in this thread based on my last couple posts...



I decided a while ago to run a 2-stage design. Cooltubed 400W, then a scrubbed exhaust for the grow area.

I am reconsidering the cooltube and thinking about swapping the cooltube for the type of design red uses, i.e. having the light at a fixed height, inside of its own chamber with a glass bottom.

My question: Has anyone done that and found an effective and clean way of running ducting from the grow area, through/past the chamber with the light, and then to the top of the cabinet where the scrubber and exhaust are?

Pics would be perfect since it's hard to explain.

 

[DaftBud]

Hey guys. I'm sorry if this seems off-topic, but I think it's more related to ventilation than to anything else.

In short, the only place in my house I feel comfortable running a grow is in my bedroom, which is already the hottest room in the house. Naturally, I'm concerned about adding to the heat by exhausting straight into the open air. As a result, I had planned to run an exhaust duct from the cab up through a hole in the ceiling and into the attic.

This all seemed well and good until I saw a show where these people were having their home renovated after discovering the former renters had been using it as a grow-house. There was mold all over the wooden light-traps they were using to bring air in from outside and that got me concerned that the air (which I assume will be warm and humid) coming from my exhaust would cause mold to start growing on the wood in the attic.

Is this the case? Should I suck it up and exhaust right into the open air? Am I stupid?

 

[simon]

I didn't read the entire thread. Please forgive me if this was already addressed.

Let's look at the intake setup above. As air will always follow the path of least resistance, the bulk of the airflow will come from the intake closest to the exhaust. Once that (specific) intake vent's ability to flow is exhausted - no pun intended - the second intake begins to flow more air. As such, in a config like the one illustrated above, the bulk of the incoming air won't be drawn across the garden until the intake on the right is close to being max'd. This condition is easily solved by placing the intake vents opposite to the exhaust.

Simon