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Ventilation: what size of fan you need

woody

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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

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@sanguine
On a serious note, I noticed that in my 4x4x around 7 foot tall tent, it took about an hour to clear the tent of the cigarette smoke smell, after I had my wife smoke one in the tent to test odor control. Should that smell have cleared out sooner?
 

woody

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@sanguine
On a serious note, I noticed that in my 4x4x around 7 foot tall tent, it took about an hour to clear the tent of the cigarette smoke smell, after I had my wife smoke one in the tent to test odor control. Should that smell have cleared out sooner?
Im not really sure about that one mate- its more likely that the cigarette odour got onto something in the tent- not that there was actual cigarette smoke still in the tent.

But whats more important is that you didnt smell it outside the tent. Then you knoe the fan and filter is doing its job right
 

Dichoti

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I was hoping. I've only got a 4" fan and carbon filter in there. Odor control is one of my biggest concerns, because I live in the ghetto, and don't want some junkie or tweaker smelling it, and trying to get into my house. I've got two mean ass dogs that barely let ME into the house at night, and I'm the one that feeds them... Hate to see what would happen to a junkie.
...although, If they caught someone coming in one of the side windows... I'd have a few months worth of "organic ferts" for the tomatoes I'm going to grow too.
 

thedope

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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-4-6-8-Inch-Inline-Fan-Hydroponics-Exhaust-Fan-Duct-Cooling-Fan/331835934649?epid=1966337412&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-4-6-8-inch-Air-Carbon-Charcoal-Filter-Odor-Control-Scrubber-for-Fan/172810741794?epid=1573556714&hash=item283c52a822:m:mlzuYi1BtTSa7jILbWNP_Yw

Hope that helps.
 
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