Exhaust fan for grow room help please!

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Purplehaze01

Member
Hi I have a grow tent which is Width 50cm x Length 50cm x Height 100cm and will use a 250watt HPS light

I will have 2 fans below and above my plant and I'm pretty sure i'll need an exhaust fan at the top of my grow tent. My room outside the tent is pretty warm but hopefully that's not a problem? I would like to know how much CFM I'll need my exhaust fan to be and if the setup will be okay

Thanks!
 
squishbox

squishbox

Member
400cfm exhaust should do the trick for a 1x1x2. It should be enough to create negative pressure (which will help with the smell). You will also want to have a passive intake setup at the bottom of the tent, bringing in fresh air. I would consider pointing a clip fan directly at your lamp (if it is not an air-cooled hood). It can help a lot with ambient temps. Best of luck.
 
squishbox

squishbox

Member
Purplehaze01 said:
Thanks for the reply bud! I have these rectangle holes (2 of them) with a netting, is that okay to allow air through?
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Perfect. Although, it can be a pain in the ass if they let any light in during the night cycle. What I did with my tent was tape up the flaps, and cut a small hole at the base, and rigged some ducting up to a small 4inch booster fan to pull in fresh air. Pulls in fresh air, keeps light out.
Purplehaze01 said:
Nah i havn't yet.. I'm sure it will.. What do you think I could do to help?
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A small window ac unit would definitely be a good investment.
 
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Purplehaze01

Member
Yeah that's what I was thinking my friend. I checked how it would look with the lights off and everything and it was really dark in there (hardly any light). Ah that's a good idea.. Could I just use any fan to pull the air through? Like a regular table fan? Hmm.. How much will that cost? I'd prefer not having to use any windows because of the position the tent is in.. I'd like a really cheap method if possible
 
squishbox

squishbox

Member
Purplehaze01 said:
Yeah that's what I was thinking my friend. I checked how it would look with the lights off and everything and it was really dark in there (hardly any light). Ah that's a good idea.. Could I just use any fan to pull the air through? Like a regular table fan? Hmm.. How much will that cost? I'd prefer not having to use any windows because of the position the tent is in.. I'd like a really cheap method if possible
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A 4inch booster and some ducting would probably run you about $30. 400cfm exhaust, about another $20. I'm not sure you would get the same effect with a table fan. Give it all a test run like Bubblin suggested, and if you are reaching the mid to upper 80's, maybe consider running your lights during the night when it is cooler. Ideal canopy temps 74-78f, 30-40%(ish) RH. Wish you luck.
 
Uberknot

Uberknot

Well-Known Member
really? 400 cfm for 50cm x 50cm x 100cm tent? you sure it's not gonna just implode as soon as you turn it on???
 
squishbox

squishbox

Member
Uberknot said:
really? 400 cfm for 50cm x 50cm x 100cm tent? you sure it's not gonna just implode as soon as you turn it on???
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Works for me just fine. I use the same size tent to flower out males. No imploding. I figure it's better to have a little overhead, considering 240cfm, and 100cfm fans cost exactly the same amount as the 400's. Can always dial it down with one of these, although I haven't seen the need to:

https://www.amazon.com/Apollo-Horticulture-Variable-Router-Controller/dp/B01C7PA5NM/ref=sr_1_2?ie=UTF8&qid=1468107601&sr=8-2&keywords=inline+fan+speed+controller

What would you recommend?
 
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Purplehaze01

Member
Ah that's awesome.. I'll have to think about that.. If I was to calculate the CFM tho, would that be 1.6 x 1.6 x 3.2 for my room? think thats in feet.. which then divide by 3 is about 25.. so 25 cfm?
 
GuyLeDuche

GuyLeDuche

Well-Known Member
Purplehaze01 said:
1.6 x 1.6 x 3.2
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^This is literally the equation for figuring cubic feet per minute lol. Multiply length x width x height = cubic feet of space. You want to change your air every minute or so, making the math easy for CFM...

Worth noting that though fans say things like "200cfm" that refers to perfect conditions, often a 200cfm inline booster will only run about 80-100 actual cfm IME, so it's worth going bigger, but 400 cfm does sound like alot to me for that space...
 
Mount

Mount

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