Fan size and filtration

**AutoManCan** · 22-05-17, 04:41 PM

Hello all,

I have just been to a local Hydro shop enquiring on fans and have come away empty handed and unsure what to do.
After doing much reading I thought a 4" fan with a 4" carbon filter would be adequate for my Groom and wanted to pick your brains for help.

The space I have is 3.5' wide x 3.5' long x 15' high.
I propose to grow 2no Auto plants in 12L or 15L pots using a single 250w HPS for my lighting.
The ambient temperature of the room recently has been around 17-18°C during the daytime (This is before any kind of mylar application or lighting being installed).
I plan on running the light over the nightime hours to keep temperatures up and more stable.

I was led to believe that to calculate the size of exhaust fan you need to exchange the air volume of the grow room once every 1-3 minutes.
As I have 168 cubic feet I need to exchange at least 56CFM. Most of the in-line 4" fans I have looked at state they shift around 80-130CFM which is gicing me around 50% headroom if I go for the higher rated ones.

I was going to couple this with a cheaper 4" carbon filter from eBay which is rated at a maximum scrub of 150CFM which is more than the fan would push through anyway.

Now on the intake side I wasn't going to bother as I was told you only need to worry about intake if the temperatures are too high and I need to bring in cooler air.
The room contains a boiler you see (doesn't increase the room temp much at all) and the walls contain a couple of air bricks, which I was told would be adequate.

Now the bloke in the hydro shop told me in no way would a 4 inch cut it and I should never use a 4" in-line for an extraction.
He then told me I should buy a 4" in-line for the intake and a 6" for the extraction along with a 6" carbon filter.
I may be wrong as I am a complete novice, but this just seems like complete overkill to me, a 6" extraction he was proposing would give me around 325CFM :O surely this is way more than I need.
Also the carbon filter he was proposing has a maximum scrub of around 350CFM :O

What do you guys reckon?
Would the 100mm inline TT with a matching 4" carbon filter be adequate?

TIA
AMC

Viz · 22-05-17, 04:52 PM

Hello matey could you redo your grow space dimensions for me. Am I correct in seeing your height is 15 foot?????

CM's would make life easier and no confusion that way.

**AutoManCan** · 22-05-17, 05:01 PM

Originally Posted by Viz

Hello matey could you redo your grow space dimensions for me. Am I correct in seeing your height is 15 foot?????

CM's would make life easier and no confusion that way.

I usually use CMH but see alot of CFM on this site so wasn't sure which to use.

Yes the height is 15'. It is a boiler room on my extensiona nd the boiler is 9' above floor level so the heat doesnt come down to ground

In metres it is as follows

0.97m x 1.02m x 4.57m = 4.52m³

4.52m³ x 20 exchanges per hour (1 every 3 minutes) = 90.4 CMH

The Vents TT 4" in-line is rated at 145CMH on slow and 187CMH on high.

Viz · 22-05-17, 05:46 PM

Right got you.

Will be shooting a pm over with a link to the formula that measures all the stuff you want. It includes things like what to minus in cool basements or what to increase if a warm attic.

Personally for that space I would use a 5" RVK L1 extraction fan and a Rhino Pro carbon filter. I certainly do not believe in messing around with odour control or providing the right air circulation for my grows. To me it is more important than the lights I select even.

PM sent.

**AutoManCan** · 22-05-17, 06:10 PM

Thanks for the PM Viz but I can't reply yet until I get 20 posts.

So if I use those calculations I get the following :

0.97m x 1.02m x 4.57m = 4.52m cubed.
4.52m3 x 60 minutes = 271.2CMH
271.2CMH X 1.33 = 360.7CMH

judging by this I am best off using a 6 inch YT? fan which shifts 552CMH as the 5 inch only shifts 280CMH.

What do you reckon to intake?

I get what you mean. Odour control and air shouldn't be scrimped on.

Lighting is easy.

**CloneBonerStallone** · 22-05-17, 07:00 PM

I'd say you should get the 6" fan and filter.

You should get a fan speed controller too. This way the fan runs quieter and you still are moving enough air to keep things cool and clean.
You don't want the minimum size fan running at full speed all the time to rely on. Better having more and not needing it then to not have enough.

Viz · 22-05-17, 07:05 PM

Look I am a huge fan of the RVK products, the 6 inch L1 is a very good fan, and the Rhino Pro filters are considered by most to be the best. Pricey for sure but it is worth it.

Intake of fresh air. There you can just go passive even if you duct in fresh air from outside your exhaust fan will drive the negative pressure in that space and suck in the fresh air. Personally I would want to put a 1m x 1m x 2m grow tent in your space. Or 90 cm c 90 cm x 200cm even. Big enough for one good plant. Or two smaller one. Again personally one good plant will outperform two so so plants. Quality over quantity every time.

**M_C** · 22-05-17, 07:16 PM

That's good thinking by Viz...

I second his idea of using a tent in your space, it'll be easier to work with

Sent from my SM-G900F using Tapatalk

**Admiral** · 22-05-17, 08:56 PM

If your pushing out 200+ mh you should be fine in that space with a 250w. 250-300 mh would be perfect. And as stated, tent FTW

Viz · 22-05-17, 09:05 PM

If you are in a tent your total volumetric space is so much smaller that you could happily use a RVK 5" L1 fan, and corresponding Rhino filter. That will cut nearly the full cost of the tent from your total. Hydrolap tent 100x100x200 cost under £100 for example. Now the difference between a 5" fan and filter system and a 6" is about £80 last time I looked. No brainer I would suggest. Get a tent and happy days.