Exhaust opening vs CFM vs grow area (inquiry)

Hi gals, so I have this room all ready and set for my first time growing.. or thats what i though when i started investigating. Its a nice 7 x 6 x 13 ft room in a basement, specifically in a cellar, with no windows, a door entrance and a magical atmospheric exhaust pipe leading straight outside through the wall (about 1 foot thick), used on the old houses to offer some air to the basement. All good so far, but here is the trick; its only just over 4 inch in diameter. So even tho i could use a whole room for grow here its simply impossible as far as i see it, in terms of CFMs i could push through the opening.

So, now the question arises, how much could i get away with in terms of the size of the growing area with this kind of outtake. In essence 4 inch hole as far as i know will lug 50 CFMs no more. I d put a bit stronger fan in there but i doubt it would make much of a difference.

So am i stuck here with 50 cubic feet to work with, if i go by the general number of 1 air exchange per minute? I mean, i know higher CFM is beneficial for the heat dissipation but if i manage to get heat down via some other resource (CFL, cooltube?) can i go for like 250 cubic feet, that is 1 air exchange per 5 minutes, main objective being to get the O2 out?

Mind you its in a basement and and its a very cool place, it was used as a wine cellar up until recently. Pretty moldy tho, i ll have to go work on that and humidity is pretty high, from 90 with everything sealed, down to 80 with a little breeze and down to 70 if i get a good air exchange happening through out the basement.

Im just disappointed a bit that my exhaust pipe wont work for a space that is attached to it. But i d want the best yield for this air uptake that i can create in relation to a pretty cool place i can nest in.

What do you recommend for this setup in terms of grow area, number of plants and lighting for max yield?



Thanx for your answers, i appreciate it!

I built my rooms in my basement. 8x5x7 for both an I have an 8 inch fan and ducting and used a reducer down to a 4 inch exhaust vent. Produces a very strong negative pressure in both rooms super high air exchange rate and absolutely no stink leaks out. Hope that helps and beware the mold might want to scrub the walls with bleach to kill it

I use a 4" blower which is around 150cfm max. 6" carbon inline filter. 10x20x1 6" filter box with a Merv 13 filter to keep dirt from stopping up my carbon filter. I played around and found a 10x20 filter frame at one bottom of a wall is good. Any more and when my AC or heat kicks on it may pull some stink from the area.

xdream said:

Hi gals, so I have this room all ready and set for my first time growing.. or thats what i though when i started investigating. Its a nice 7 x 6 x 13 ft room in a basement, specifically in a cellar, with no windows, a door entrance and a magical atmospheric exhaust pipe leading straight outside through the wall (about 1 foot thick), used on the old houses to offer some air to the basement. All good so far, but here is the trick; its only just over 4 inch in diameter. So even tho i could use a whole room for grow here its simply impossible as far as i see it, in terms of CFMs i could push through the opening.

So, now the question arises, how much could i get away with in terms of the size of the growing area with this kind of outtake. In essence 4 inch hole as far as i know will lug 50 CFMs no more. I d put a bit stronger fan in there but i doubt it would make much of a difference.

So am i stuck here with 50 cubic feet to work with, if i go by the general number of 1 air exchange per minute? I mean, i know higher CFM is beneficial for the heat dissipation but if i manage to get heat down via some other resource (CFL, cooltube?) can i go for like 250 cubic feet, that is 1 air exchange per 5 minutes, main objective being to get the O2 out?

Mind you its in a basement and and its a very cool place, it was used as a wine cellar up until recently. Pretty moldy tho, i ll have to go work on that and humidity is pretty high, from 90 with everything sealed, down to 80 with a little breeze and down to 70 if i get a good air exchange happening through out the basement.

Im just disappointed a bit that my exhaust pipe wont work for a space that is attached to it. But i d want the best yield for this air uptake that i can create in relation to a pretty cool place i can nest in.

What do you recommend for this setup in terms of grow area, number of plants and lighting for max yield?



Thanx for your answers, i appreciate it!

Click to expand...

a 4" vortex will flow fairly nicely, I used one for yrs with two 400w hids
what I would do, if you are intent on using this area, i'd go with a LED panel over a HID setup, the airflow is FINE for the plants, the issue is the heat, so an led panel would solve that issue.
past that if you get hids it'll get hot, and potentially with the added heat, brings more water transpiration, and that in a less-than-optimal ventilation+basement = mold.

dandyrandy said:

I use a 4" blower which is around 150cfm max. 6" carbon inline filter. 10x20x1 6" filter box with a Merv 13 filter to keep dirt from stopping up my carbon filter. I played around and found a 10x20 filter frame at one bottom of a wall is good. Any more and when my AC or heat kicks on it may pull some stink from the area.

Click to expand...

That's why I create negative pressure in the room then I know it's getting plenty of fresh air in and nothing exits the room unless it goes Thur the filter to outside. I've had family over and no one knew they're were standing on top of 24 ish plants. And I have central heat and air.

Thanx, peeps, for the input.. Lordhooha, as far as i see, your room in something like half of mine in volume, i think reducing mine to that volume would probably be enough for getting the room very close to the best balance with other factors in play here.. How much do u pull off your plants in average?

Im a bit obsessed here to getting the room in perfect balance in any case, most of out peeps out there wold go with max space they have never minding other variables however i question this is right approach in terms of the max yield possible..

I would go with LEDs as greasemonkeymann suggests but of course problem would be the cost for these (do u have any good and economic suggestions here, monkey?) and so i think i will have to use HIDs one way or another, I guess with the volume reduction, cool tube? and dehumidifier after a while..

however, this got me thinking.. no one really went after my claim that the bottle neck is always the most of what an exhaust can pull in terms of CFM, however CFM is not the same as speed created by the negative pressure of an outtake.. negative pressure, if i speculate right, should produce faster speed of an outtake but it will tug less CF per minute.. and i think speed of air moving would help the odor and heat dissipation but not the air as a whole moving/replacing faster.. thats just speculation, please, correct me if this isnt really so in your experience.. i any case i am following something written on this forum ( https://www.rollitup.org/t/what-you-need-to-know-about-exhaust-fans.292873/ ) and to me it seems a pretty credible analysis..

So I guess we could say that higher negative pressure should create more blow on the lights and better odor control, but i wonder how many plants would give their maximal effort in this environment where used air wouldn't be replaced as fast as in a smaller place. I guess this relation is pretty timely to measure or test accurately, so it doesn't come up as variable to consider in lots of grow room plans.

xdream said:

Thanx, peeps, for the input.. Lordhooha, as far as i see, your room in something like half of mine in volume, i think reducing mine to that volume would probably be enough for getting the room very close to the best balance with other factors in play here.. How much do u pull off your plants in average?

Im a bit obsessed here to getting the room in perfect balance in any case, most of out peeps out there wold go with max space they have never minding other variables however i question this is right approach in terms of the max yield possible..

I would go with LEDs as greasemonkeymann suggests but of course problem would be the cost for these (do u have any good and economic suggestions here, monkey?) and so i think i will have to use HIDs one way or another, I guess with the volume reduction, cool tube? and dehumidifier after a while..

however, this got me thinking.. no one really went after my claim that the bottle neck is always the most of what an exhaust can pull in terms of CFM, however CFM is not the same as speed created by the negative pressure of an outtake.. negative pressure, if i speculate right, should produce faster speed of an outtake but it will tug less CF per minute.. and i think speed of air moving would help the odor and heat dissipation but not the air as a whole moving/replacing faster.. thats just speculation, please, correct me if this isnt really so in your experience.. i any case i am following something written on this forum ( https://www.rollitup.org/t/what-you-need-to-know-about-exhaust-fans.292873/ ) and to me it seems a pretty credible analysis..

So I guess we could say that higher negative pressure should create more blow on the lights and better odor control, but i wonder how many plants would give their maximal effort in this environment where used air wouldn't be replaced as fast as in a smaller place. I guess this relation is pretty timely to measure or test accurately, so it doesn't come up as variable to consider in lots of grow room plans.

Click to expand...

I tested my room after I got it all framed up drywall up and happy by sitting in the with the door such and smoked my hookah. Cut my fan on with the speed controller on the high pend of the low setting( if that makes sense lol ) and it pulled all that smoke out in under a min. For lights I do LEDs any more I have several cheap costing guys I bought for my reef tank some years ago. They have a bunch epistar 3 watts in it they do pretty good and you can pick them up super cheap. I'll hunt it down so you can see. I use them for cloning and babies now. For my main room I have a kind led xl1000 and I built me a cob led using a hps hood I got off eBay for 50 buck sheet metal from Home Depot and replaced the glass with that made it look pretty nice for little money. With both of those guys running my room sits at 78 degrees with only one running75 to 76 degrees. As for the negative pressure deal they do really well you have that constant fresh co2 enriched air flowing in. As for the bottleneck that little four inch vent just forces it out it's like a mini hurricane it doesn't seem to affect the fans ability to perform nor does it seem to put any extra load on the fan. But it's one of those orange ones from HTG with a five year warranty and I know the guys that run the one close to me so I don't worry if they'll honor the warranty. Once you get that exhaust fan running depending on where your located it should go down without the need of a dehumidifier. For reference I'm in Michigan. And last my average yield varies by strain and the amount of plants I'm running at the time. Let's just say I hit 2.5 per plant but let's just focus on getting you up and running first. I will also suggest you get you a notebook and write down everything you do in your room what you fed them how much temps RH in the room and I even add the time when I done it. This might be overkill but it's that attention to detail the military beats into a person. Lastly try and keep your grow area as clean as a hospital surgery room. Now let me go find those cheap ass lights.

Here it is like I said I use to have six of them over a 150 gallon tank growing coral and such once I took it down I repurposed them and not bad considering I picked them up for 75 bucks a piece.

https://www.amazon.com/AQUAMANA-LED-55x3W-Dimmable-Aquarium-Light/dp/B00FHDEAFQ/ref=cm_cr_arp_d_product_top?ie=UTF8

Thanx again for your reply, i actually found a few DIY LED panel projects on this site and being an avid electro DIYer those should be a piece of cake so i most definitely will go with these.

xdream said:

Thanx again for your reply, i actually found a few DIY LED panel projects on this site and being an avid electro DIYer those should be a piece of cake so i most definitely will go with these.

Click to expand...

Easy easy man if you can wire a plug for your house you can build a good cob led. Like I said I used a aircooled hps hood so I can air cool mine rather than run fans.