Ventilation: what size of fan you need

One of the most common questions i see new growers posting....
What size of extraction fan and carbon filter do i need for my tent?
Extraction fans are rated in m3/hour

Heres the simple answer for some of the most common tent sizes.

0.6m x 1.2m x 2m = 115m3/hour
1m x 1m x 2m =160m3/hour
1.2m x 1.2m x 2m = 230m3/hour
1.5m x 1.5m x 2m = 360m3/hour
1.2m x 2.4m x 2m = 460m3/hour
2m x 2m x 2m = 640m3/hour
2.4m x 2.4m x 2m = 920m3/hour

So find a fan that meets the airflow needed for your area if it takes a 125mm/5inch fan then you need the same size of carbon filter and ducting.

If you want to learn how to work this out for yourself in any size of tent or grow room keep reading.

Firstly work out the volume of your grow space (length x width x height) then multiply this number by 60. This gives you the maximum amount of air you need to exchange each hour.

So for example a 1.2 x 1.2 x 2m tent gives you a volume of 2.88m3, multiply this by 60 and you have 172.8m3/hour.
At the moment, a 100mm (4”) RVK100A1 fan seems suitable for this scenario with an air moving capacity of 175m3/hour. However, it does not consider the impact of attaching a carbon filter and ducting…

To factor in the expected fan speed reduction of around 25%, multiply the original calculation by 1.33.

So 172.8m3/hour x 1.33 = 230m3/hour.

Other factors to consider.

- Add 20% for a warm attic

- Minus 15% for a cool basement

- South facing rooms will tend to be hotter than north facing rooms – increase the size of fan and use a fan controller for exposed areas

- Add 20% for long ducting runs and/or multiple bends

- If incoming air is 25oC or above then the room will become hot irrespective of the ventilation – an OptiClimate System or Air Conditioning Unit is the only solution

- Minus 25-30% for air cooled lighting

 

[Dichoti]

It's only gonna be 180ws so don't expect loads but what u get will be very frosty

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A few reviews I've read on other forums put it as "a lot brighter than my 600w" and "almost as bright as my Platinum something or the other". We'll see though, because I don't know how good any of the stuff I have is, yet.

 

[Autoflower420]

A few reviews I've read on other forums put it as "a lot brighter than my 600w" and "almost as bright as my Platinum something or the other". We'll see though, because I don't know how good any of the stuff I have is, yet.

I have 6x800s they draw 180 I have 2x800s that draw 250 same make same light I have 2x900s that draw 500w led company blag u some when u see a led light that says 900 that usually means it's equivalent to 900w of hps

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[Autoflower420]

A few reviews I've read on other forums put it as "a lot brighter than my 600w" and "almost as bright as my Platinum something or the other". We'll see though, because I don't know how good any of the stuff I have is, yet.

What make is it

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[Dichoti]

What make is it

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I'll go look for a name on it later on, because at the moment, I don't remember seeing one. I do remember it's got 1000 watt on one decal on the back, and it's got 180- 200 watt wall draw. It's just some cheapie I bought because people were complaining about it turning their tops white.

 

[Autoflower420]

I'll go look for a name on it later on, because at the moment, I don't remember seeing one. I do remember it's got 1000 watt on one decal on the back, and it's got 180- 200 watt wall draw. It's just some cheapie I bought because people were complaining about it turning their tops white.

Sounds like mine boss led

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[Dichoti]

Sounds like mine boss led

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If I remember right, mine's white though.

 

[Autoflower420]

If I remember right, mine's white though.

Yes they make them in white or black they just sent me 2 800s and 2x900s but the 900s draw 500w and the 1200a only.draw 400w so they all crazy like

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[Masterkush87]

So my tent is 80*80*160 cm, per my calculation i need 81.7152 m3? Am i doing something wromg can someone help? I am growing 3 plants in the rainforest hydro, and atm i have that 1000w cheapo led its so bright i have used it in previous soil grows and really quantity was dependent on how much i screw up but always frosty like a mf! Should i get another one or do u guys recommend a specific light? Led preferably

 

[Snidely Whiplash]

Hi all! long time lurker first time poster

I'm a novice grower but I design odor control systems for many industries like plastic extrusion vents where the odors and VOC's are pretty high. Working out your carbon filtration is really just a matter of doing some math. Hopefully some of you will find this useful.

For carbon to work properly the smelly air needs a certain amount of "dwell time" in the carbon. I see a lot of people use fan systems that are too poweful and the air gets pulled too quickly through the carbon. Get in touch with these guys http://www.generalcarbon.com/ and ask for a carbon pellet that is formulated for cannabis. potassium permanganate and coconut Shell are another odor absorption medias that work well. There are literally 100's of different carbon formulas for VOC and odor control.

To work out your cfm needed for 10 air changes per hour you multiply your fan systems cfm x 60 and divide by the volume of the space. For example...if a 4" cent' fan has a cfm rating of 187cfm - if your grow space is 6' x 8' x 8' then 187x60=11,200/384 = 29.1 ach.

So..a 4" fan that does 187 cfm running on full speed with an line carbon filter is pulling too fast and the air is not getting adequate "dwell time"...but that same fan running at 1/2 or 1/3 speed is going to be much more effective.

I hope this info is useful..

 

[Blitzen]

At 4 x 4 x 7 = 112 cubic feet x 2 = 224 cfm fan

I multiply by 2 for losses due to ducting. The actual losses could be less but it is a rule of thumb that ensures you will have enough power to exhaust at the rate of one air exchange per minute. In your case, 112 cubic feet is the target.

If you have 120 volt power, I recommend something like:
https://www.ebay.com/itm/Strong-CFM...hash=item4d42f687b9:m:mE3AWU1GhURsauxhYNupdtA

You might also look into a controller like this:
https://www.ebay.com/i/282266838825?chn=ps&dispctrl=1

And here is a filter:
https://www.ebay.com/itm/VIVOSUN-4-...hash=item283c52a822:m:mlzuYi1BtTSa7jILbWNP_Yw

Hope that helps.

Thank you for the information, this will help me a lot!