# Ventilation: How many CFM do I need?



## glopal (May 31, 2008)

I bought a 400 watt HPS with a 430 watt Son Agro bulb. My box is going to be 3x3x5 feet. How many CFM do I need to properly cool this beast?

I'm thinking about getting two computer fans at 59.2CFM each.
http://www.cbit.ca/mb/retail_productdetail.asp?Cat=7&SubCat=184&offset=20&ProdNo=FAN-318-410

So thats 118.4 CFM. My box is 45 cubic feet. What do you guys think?

Then if you could check out this fan...
http://www.canadiantire.ca/browse/product_detail.jsp?FOLDER%3C%3Efolder_id=1408474396672697&bmUID=1212292209105&PRODUCT%3C%3Eprd_id=845524442201667&assortment=primary&fromSearch=true

Do you think thats overkill?


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## glopal (Jun 1, 2008)

I found a cheap 500 cfm inline fan I could get. I found a formula for calculating how much cfm you need. Its your cubic feet multiplied by 12.

45 x 12 = 540cfm

I think I'm good.


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## snuggles (Jun 1, 2008)

Cutting it close there but I would think you would be fine, maybe some details here or there and maybe an extra oscilatting fan. Good luck and fill us in please.

Thanks for the formula BTW


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## Papaya123 (Jun 2, 2008)

I just have a portable ac unit in my roo, it ducts air as well, sooo it works like a cfm and also cool my room. I tried purchasing one, but dayaaaaamn they expensive son!!! Hydro shop charged me about 400 for the carbon filter, the fan, y- connector, and the lil  aluminum piping but nuthing for cooling, so i went ahead and paid $300 us for a portable wheelie rolly thingy and it vents and keeps my room temp low and i stay in there now cuz it feels good in there then my scorching hot desert of a city that i live in. I just have to wear sunglasses when i go in cuz a 600 watt mh bulb reflecting in a white room is no bueno for your eyes lol.


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## glopal (Jun 2, 2008)

Wow, what a headache. Finding a good fan is tough. I thought I found one but it turns out if you want the fan to pull air through a filter you need a fan with impeller blades. So I think I found something in my price range. I'm still not certain what cfm rating to get though.

I need an expert here, do you think 268 cfm is good enough for 43 cubic feet? Or should I get the 565 cfm one?


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## Puffin Afatty (Jun 2, 2008)

glopal said:
			
		

> Wow, what a headache. Finding a good fan is tough. I thought I found one but it turns out if you want the fan to pull air through a filter you need a fan with impeller blades. So I think I found something in my price range. I'm still not certain what cfm rating to get though.
> 
> I need an expert here, do you think 268 cfm is good enough for 43 cubic feet? Or should I get the 565 cfm one?


 
_ a buddy did a closet grow about the same size, with the same bulb.  the 265cfm was bare minimum with constant ventilation. with a large enuf intake and exhaust you'll still run 10 degrees above ambient.  I think you'd be better served with a 565 cfm._  :hubba:


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## lyfr (Jun 4, 2008)

i gotta 5x5x7 room,265cfm, 400mh/hps and its a full time(24/7) job to keep it 75-80deg.  i have a concrete floor which helps but if outside temps go over 90 im openin everything up, and using every fan i got...if that helps.


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## Exarmy (Aug 24, 2008)

Just went through this desision, heres what I ended up with

400w digi ballast
aircooled reflector
4in vortex fan (170cfm)
Elf filter
box deminsions are 28in x 26in x 40in

My light has been on since my seeds sprouted 48hrs ago. My indoor temp right now is 73.8. And inside my box its 81.8.


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## Hydraphonix (Aug 24, 2008)

I was told a formula that 2 60 cfm fans (1 for intake and 1 for exhaust) would be enough to vent my stand up freezer with a 250w hps is this accurate??


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