How to: Buying the right intake and exhaust fans

Discussion in 'Grow Room Design/Setup' started by AAckley1, Aug 28, 2007.

1. So you got your grow room setup, lights, pots, and of course, POT!

But your missing one thing, and thats ventilation. I'm going to help you along the way to making sure you have the right fans for your situation.

Most growers would suggest you replace the air in your system 20 times in an hour, every 3 minutes. Now you are probably asking, how do I do that?

Easy, calculate the area of your grow space, we'll use a 2 meter x 2 meter x 2.5 meter grow room for an example. You want that 10 square meters of area to change 20 times in an hour so you will multiple by 20.

10m3 x 20 = 200m3, but "overkill the hell of your ventalation" as suggested by Rumpleforskin so lets just say you want 225m3.

Now comes the calculator, to find the correct CFM for the system you want to use take your 225m3 and multiple it by 0.588

225m3 x 0.588 = 132.3 CFM so lets round up to 135 CFM to continue to "overkill the hell of your ventalation"

For your 10 square meter grow room, you want a 135 CFM fan to run constantly.

And there you have it, now you know what size fans to get for your growroom.

2. Thanks for posting this, it cleared this doubt that had been in my mind for a while (although I don't have a grow in mind at the moment).

3. my advice: biggest fan you can afford and a \$3 dimmer switch set up from home depot / lowes..

then crank that fukr up as high as your comfortable with

4. Hmmmm...I've always heard you should target exchanging the air in your grow space at the rate of three times per minute, not once every three minutes. If so then your calculation is off by a factor of 9.

5. My growspace is basically a rectangular shaped "crawlspace" underneath my basement stairs. Pretty big, maybe 12 feet long, 5 feet wide and 6' tall tapering down as the stairs reach the bottom. I cut a "door" out of the sheetrock and attached some magnets and a handle. I have a french drain behind the sheetrock so the wall extending to the rest of the basement has a 1.5' gap between the sheetrock and the block foundation. I am using a small fan to blow "fresh" air in from this space, but have no vent going out. Seems like there is plenty of air movement in there. Is this sufficient? The only way to vent out would be to rent a hammer drill and bust out the block foundation. I really don't want to do that. Planted 3 hashberry and 3 speed queens direct in soil 6 days ago. So far all 3 SQs popped and 2 HBs. Looking good so far under CFLs with perfect temps 78 F and 68-70% humidity. I plan on gettting a 400 W HPS set up in a week or so.

6. im growing in 11" x 23" x 14", can you calculate the CFM for me? i came up with 3952...

7. Well I got 3,542 and that in3
Converted to FEET it is only 2 ft3
I use 5X exchanges in my calcs - various reasons - biggest being that you NEVER get the full CFM on the fan - so I would target toward 10 CFM.

8. #8
Last edited by a moderator: Jul 22, 2010
~ I'm going to be setting up a new grow room and would like to know the best way
to run my air flow. This is a large room with bath and closet. The bath room would
be a great clone center. The closet could be a treatment chamber for sick plants.
The room is shaped so as to be easily divided but I feel the main body of the room
should be left open for.

~ I plan on growing 8 to 10 plants in flower. For vegging ares I figure 10 - 14 plants
and then a clone are.

~ The grow areas would be roughly 23' 13' but could be broken into areas:

13' x 13' main body of room

7' x 7' smaller section or area

5' x 10' full bathroom

3' 6" x 8' closet w/ sliding mirror doors

~ I'll be running hoods not cool tubes (yet):

1000 watt HPS (I plan to add 2 more 1000 watt HPS possibly 4 total)
600 Watt HPS/MH
2 x 400 Watt HPS/MH
Various CFLs including 3x 124 watt CFL (6500K)

I have (2) AC units for the room. A 6000 BTU window unit. A 15000 BTU rolling
room unit. As well as the Home central AC with 3 register vents in the grow space.

Air movement budget is around \$200/\$300. I need to keep it low budget untill
my next grow.

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