Grow tent ventilation/exhaust help?

So I'm planning for a 3'x3'x6' grow tent, running a 250w mh/hps. By ' I mean feet.

Problem is I don't know a danm thing about any of this ventilation/exhaust/carbon filtering stuff.

After reading up, the most common calculations say I would need a 18 CFM fan to be adequate. Equation being 3*3*6=54/3=18 and then i see it being said to add x% for blah blah but even if I add 100% I'm still wayyyy under any popular fan I can buy.

The popular lowest rated fans are about 175-190 CFM. Is that overkill?

My goal is using a carbon filter attached to the exhaust(for no smell) and obviously plant health by not over ventilating. I also see I could use a fan speed control, maybe that would be my best bet, but at what desired CFM?

I don't plan on intaking air with a fan, rather just ducting with no fan, I'd assume that would factor into needing a lil more cfm...

Ducting with no intake fan won't work if you have ducting leading into your grow room but with no fan how do you expect the air to get into your tent? With no fresh air circulation you already having plant problems lined up waiting for you...

And your out take fan won't be overkill if it is supported with a intake fan with 15 - 20 % less power so you still have negative pressure...

I use a 8" pro rhino fan accompanied with a 8" RVK fan in a 5"× 5" tent, works well Max power 950 cfm so I think a 5 or 6" would be plenty for you!

BigBud420. said:

Ducting with no intake fan won't work if you have ducting leading into your grow room but with no fan how do you expect the air to get into your tent? With no fresh air circulation you already having plant problems lined up waiting for you...

And your out take fan won't be overkill if it is supported with a intake fan with 15 - 20 % less power so you still have negative pressure...

I use a 8" pro rhino fan accompanied with a 8" RVK fan in a 5"× 5" tent, works well Max power 950 cfm so I think a 5 or 6" would be plenty for you!

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I mean passive intake, I will have a duct from inside the tent to outside the tent. Negative pressure from exhausting will pull air through that intake duct.

Would this do?

The 4"x12" one.
http://www.amazon.com/iPower-GLFILT6M-Australia-Pre-filter-Reversible/dp/B008NYF8S4/ref=sr_1_1?ie=UTF8&qid=1455989352&sr=8-1&keywords=carbon+filter

http://www.amazon.com/Active-Air-inch--Line-Fan/dp/B002JQ4N92/ref=sr_1_7?ie=UTF8&qid=1455989556&sr=8-7&keywords=active+air+fan

Use this for reference

http://www.growweedeasy.com/exhaust

I'm also confused about the whole passive intake

714steadyeddie said:

Use this for reference

http://www.growweedeasy.com/exhaust

I'm also confused about the whole passive intake

Click to expand...

Thanks I always look on that site but hadn't seen that article! btw the passive intake I'm talking about is mentioned in that article, I'm thinking 4" exhaust and then have two 6" ducts(with no fans) leading from outside the tent to inside(basically just providing holes that let air in) the tent to allow intake air:
Passive Intake

A passive intake means that you just have a fan blowing air out, and you have an intake hole to let new air in. With a passive intake, you don't have an intake fan to help bring in fresh air.

With every passive intake, make sure your intake hole is 3-4 times bigger than your exhaust hole to achieve proper suction and prevent your fan from working too hard blowing out air it can’t replace. You can also help bring air in by having more than one passive intake hole. In other words the holes/spaces for new air to come in (vents, intake fans, doors, windows) should be bigger than the hole/space where air is being pulled out the tent by your exhaust fan.

get a box fan they are a lot quieter and as the normally have a 90" ports on them they help if you need to turn a corner

Anon Emaus said:

I mean passive intake, I will have a duct from inside the tent to outside the tent. Negative pressure from exhausting will pull air through that intake duct.

Would this do?

The 4"x12" one.
http://www.amazon.com/iPower-GLFILT6M-Australia-Pre-filter-Reversible/dp/B008NYF8S4/ref=sr_1_1?ie=UTF8&qid=1455989352&sr=8-1&keywords=carbon+filter

http://www.amazon.com/Active-Air-inch--Line-Fan/dp/B002JQ4N92/ref=sr_1_7?ie=UTF8&qid=1455989556&sr=8-7&keywords=active+air+fan

Click to expand...

http://www.amazon.co.uk/gp/aw/d/B00C3GTC30/ref=mp_s_a_1_4?qid=1455996668&sr=8-4&pi=AC_SX236_SY340_QL65&keywords=4"+rvk+fan

If it was me I'd go for named brands and they are just as cheap as what you posted but probably best to listen to the other guys as I'm not an expert (yet) ditch the ducting and get some that's insulated though if stelf is a issue where you live, check the link above

Anon Emaus said:

I mean passive intake, I will have a duct from inside the tent to outside the tent. Negative pressure from exhausting will pull air through that intake duct.

Would this do?

The 4"x12" one.
http://www.amazon.com/iPower-GLFILT6M-Australia-Pre-filter-Reversible/dp/B008NYF8S4/ref=sr_1_1?ie=UTF8&qid=1455989352&sr=8-1&keywords=carbon+filter

http://www.amazon.com/Active-Air-inch--Line-Fan/dp/B002JQ4N92/ref=sr_1_7?ie=UTF8&qid=1455989556&sr=8-7&keywords=active+air+fan

Click to expand...

Show me some pics..........could you replicate something like this?

BigBud420. said:

http://www.amazon.co.uk/gp/aw/d/B00C3GTC30/ref=mp_s_a_1_4?qid=1455996668&sr=8-4&pi=AC_SX236_SY340_QL65&keywords=4"+rvk+fan

If it was me I'd go for named brands and they are just as cheap as what you posted but probably best to listen to the other guys as I'm not an expert (yet) ditch the ducting and get some that's insulated though if stelf is a issue where you live, check the link above

Click to expand...

Thanks man, yeah I looked up that rhino but i'm in US, doesn't seem like i have easy access to them without high shipping cost. But the fan i listed is by Hydro Farm and the filter is by iPower(seems like a brand name). I'm new to this venting area so not really sure.

Anon Emaus said:

Thanks man, yeah I looked up that rhino but i'm in US, doesn't seem like i have easy access to them without high shipping cost. But the fan i listed is by Hydro Farm and the filter is by iPower(seems like a brand name). I'm new to this venting area so not really sure.

Click to expand...

Hope all goes well for you mate, good luck

VTMi'kmaq said:

Show me some pics..........could you replicate something like this?
View attachment 3612730 View attachment 3612731 View attachment 3612732

Click to expand...

I'm only in the planning process so don't have pics. Didn't even buy anything yet for it. Basically its going to be an empty room with a tent in it and i cannot pull or exhaust air to outside so I'm just going to pull and exhaust from the room.

I currently run my 250w in a closet with door always open and fans to keep air moving and to cool the light and that works fine so i plan to do the same in the tent. So I don't need to factor in attaching ducting to a hood.

BigBud420. said:

Hope all goes well for you mate, good luck

Click to expand...

Thanks man, i appreciate the feedback!

Anon Emaus said:

I'm only in the planning process so don't have pics. Didn't even buy anything yet for it. Basically its going to be an empty room with a tent in it and i cannot pull or exhaust air to outside so I'm just going to pull and exhaust from the room.

I currently run my 250w in a closet with door always open and fans to keep air moving and to cool the light and that works fine so i plan to do the same in the tent. So I don't need to factor in attaching ducting to a hood.

Click to expand...

Ditch the tent and hang the light in the open room.. exhaust should go into the attic..

mr sunshine said:

Ditch the tent and hang the light in the open room.. exhaust should go into the attic..

Click to expand...

I plan to eventually have another tent in the room, one veg and one flower. So that won't work, also will be easier to control smell in the tent among other things.

Any thoughts on the items I listed being adequate for a 3x3x6 tent?

Anon Emaus said:

I plan to eventually have another tent in the room, one veg and one flower. So that won't work, also will be easier to control smell in the tent among other things.

Any thoughts on the items I listed being adequate for a 3x3x6 tent?

Click to expand...

Tents are harder to keep cool smell won't be any better in a tent, its made of fabric.

You need to exhaust the tent into the attic. If you exhaust it into the room the tents in it will eventually get way to hot.

Well then ......i still like tents. Not hard at all to keep kool silly.

Do you plan on using an air cooled hood, like a cool tube? I would suggest you do so. An open bulb in a tent would get pretty warm, regardless of how many cfm's. Currently I have 3 tents in my room. 4x8 with 2x 600w cool tubes on a 6" 440 cfm fan. (Filter > Fan > Lights > exhaust). Also a 4x4 with a 6" 440 cfm, and a 2x4 with a 4 bulb T5 with a 190 cfm fan. All using the passive intake flaps on the bottom, all exhausting out the window. If you are going to run HID lights, I would suggest using a 440cfm fan. You can always use a speed controller to slow it down, but if you get a fan that is not powerful enough, you can't turn it up.

blackforest said:

Do you plan on using an air cooled hood, like a cool tube? I would suggest you do so. An open bulb in a tent would get pretty warm, regardless of how many cfm's. Currently I have 3 tents in my room. 4x8 with 2x 600w cool tubes on a 6" 440 cfm fan. (Filter > Fan > Lights > exhaust). Also a 4x4 with a 6" 440 cfm, and a 2x4 with a 4 bulb T5 with a 190 cfm fan. All using the passive intake flaps on the bottom, all exhausting out the window. If you are going to run HID lights, I would suggest using a 440cfm fan. You can always use a speed controller to slow it down, but if you get a fan that is not powerful enough, you can't turn it up.

Click to expand...

Current plan is to just use a clip on fan blowing across bulb(no cooltube) like I am doing now to keep it cool, works very well. I can hold my hand a few inches under it and it's not hot. It's only a 250w HID so not really that bad.

I've seen exactly what I am describing done just fine but the guy who does it just doesn't know what cfm his fan is, so that's why I am trying to just find out the proper cfm fan to buy. But I'm coming to the conclusion there are too many different ways that everyone does this so i think trial and error(or well hopefully no error) will be my best bet.

I hear ya on the bigger with a speed control, that was one of my original thoughts, at least then like you said I can always go down without getting stuck not being able to go up. After some reading it sounds like that could increase the amount of sound from the fan too though so idk. I guess I just gotta make a decision, I basically just want to get a first tent set up to get an understanding of controlling a tent before getting another one so we'll see.
Thanks for all the info man I really appreciate it!

Tent temp is relative to the room it's within. Goal is to keep it as close to the room temp. More airflow, closer you can get. I can keep all 3 within 5 degrees of the room. The fans are not that loud at all imo. I just got the $60 ones on eBay. They work great. If you do upgrade to a 600w for example, get the kit with an air cooled hood.
Example of how I set them up.