Fan + Filter Help.

**tripppy101** · 03-01-10, 08:02 PM

Hi,

Just Want to see if my calculations are correct.

The air in the grow room needs to be changed around 3-5 times/minute (I think, from reading online)

So if my grow room is 1.6m3 and I get a 175m3/hour (cheapest) fan that is 2.91m3/minute (not including filter resistance) so the air gets changed 1.8 times a minute. So not enough.

But anohter calculation i've seen is that air needs to be changed 20 times an hour so 1.6 x 20 = 32. So plenty.

So i've got two calculations and one is saying nowhere near enough and the other is saying that it is more than enough.

What's your advice?

**The Lost Soul** · 03-01-10, 08:38 PM

Depends on what strength of light you're using as regards to the size of space you have and how hot it could get in there. Set it all up and do a test run, it's the only way to get your temps right imho.
Will it be ventilated?
I grew in a space 75x75x2.3 with ventilation into the loft and a 400whps.
I bought an RVK 150L1 150mm and it did the trick.
I would use a minimum of 125mm extraction if you're usin hps.
Hope this helps mate.

Oh aye, a carbon filter will reduce your extraction rate by up to 50% depending on the make and size/airflow of your fan.

**tripppy101** · 03-01-10, 09:01 PM

Can't test as i'm looking at what I need to buy.

I will most probably be using 250w mh/hps but slight chance of 400w (depending on money). The air will hopefully be exracted through the filter into a small outside toilet whcih always has a window open. I will also set up an intake fan which would be made to come on when the extractor comes on through a reverse thermostat (swiches on when temperatures increases to certain point rather than falls).

In previous grows i've used other fans which were lying around, not rvk or anything similar, just a combination of 2 or 3 and the max temp with 250w was around 30-32 on hot days (average 26). I need to change this setup as smell is becoming more of problem and I know my little fans won't push through a carbon filter.

**BudMan** · 03-01-10, 10:23 PM

Originally Posted by tripppy101

Hi,

Just Want to see if my calculations are correct.

The air in the grow room needs to be changed around 3-5 times/minute (I think, from reading online)

What's your advice?

Its more along the lines of stale air removed once every 5 mins dude..

"The fan should be able to replace the air volume (LxWxH) of the grow room in less than 5 mins"

**tripppy101** · 04-01-10, 01:41 PM

Thats seems more reasonable, Thanks

**tripppy101** · 11-01-10, 06:11 PM

Where should the carbon filter be positioned for it to work best, (if it makes any difference).

Should it be attached to the extractor fan and positioned by where it's going outside and the ducting sucking from the grow room? (if this then should the extractor suck air from the top of the grow room or mount some ducting so that it sucks the air close to the light)

or

Should the filter be mounted on the inside wall of the grow room at the top and the extractor sucking air through that. (if this then should the extractor be as close as possible to the filter or does it not matter?)

Thanks