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Over Sized Carbon Filter & Can Fan Or Inline Fan?

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While talking to a Hydro Shop today, and lining things up to buy for my system that I am building I heard some things which honestly confused me, and then later had me doing some researching the questions and that lead to a couple of really great posts one on Ventilation, and another on Carbon Filters. Truly an eye opening post fully of amazing details, but surprisingly it didn't help to answer my questions enough to be satisfied which has me here to try to learn even more yet.

Okay to put as simply as I can about 12-years ago I had the inside of my house as my grow room, and then one day I came home and I didn't even have curtains on the windows or dishes in the kitchen. Thus I had to start all over from scratch as someone decided they needed everything so much more than I did, but now I am ready to start all over. Only this time I have been putting together a simple but I believe a smart plan, I am going to not just buy cheap and hope it works, or go middle of the line and upgrade every step of the way either. Instead I have a long term layout planned, and I would rather buy a good Bluelab Meter upfront now and save the hassles of a cheap meter and loosing tons in crops, nutrients, electricity, and time, etc... So here is how it applies to the Carbon Filter and Fan...

Starting out to get everything dialed in I am going to start out with a 2-foot by 2-foot, by 4-foot ceiling, and go with an LED light which will cover a 4-foot by 4-foot space, because I know the first long term goal is to get my space back up to 8-foot in length, 4-foot in width, and a ceiling of 6 to 7-feet. However I know enough to start out small, and if I have problems lose six plants in aeroponics, and start another six over again from clones. Once I can get six plants up and healthy and making a full successful cycle, then expand more and do it again, over and over again until I get my room size up to the size I want to. The Hydro Store asked me how big is the space I am working within, well I was honest and explained it as I did here.

I want an 8-inch fan, and an 8-inch carbon scrubber to match, somewhere I think I saw two 8-inch carbon scrubbers one was long then the other, both had the same widths, so I want the longer one for sure. It did not say how many CFM's they could filter, so I would rather be oversized than undersized within reason of course.

The three types of Fans I was really wanting to dig more into were:
#1- Hyper Fan 8 in Digital Mixed Flow Fan 710 CFM
#2- Vortex S Line S-800 8 in Fan 728 CFM
#3- Vortex Inline Fan 8in 747 CFM

I was taught everything old school from people that used the Can Fans and Carbon Scrubbers, but when I am looking on Youtube of course now I am seeing things like the Hyper Fan being ducttaped onto a Carbon Scrubber, I would have used a neoprene clamp myself and then sealed it up with some good tape as a secondary measure. But I believe in better to do to much than have the nosey neighbors knocking on your door to see what you are doing.

The guy tells me that for my 2x2x4 foot space I only have 16-cubic feet, yeah I know I did pass math class. But I pointed out my goal space for this unit will be 8x4x7- feet which is 224-cubic feet.

1. I'm adding 5% per air cooled light or 10-15% per non-air cooled lights.
2. CO2 — add 5% for rooms with CO2 enrichment
3. Filters — if a carbon filter is to be used with the exhaust system then add 20%
4. Ambient temperature — for hot climates (such as Southern California) add 25%, for hot and humid climates (such as Florida) add up to 40%.
* It will get into the 90's-100+ here in the summer with high humidity.

So yeah I am going overkill on my fan, so I can use a fan controler to underclock the fan speed to make it quieter, and then if I need more air moving for carbon scrubbing or to move more air around I can turn it up as well as down. But the last thing I'll have to worry about is having an issue so as long as my fan doesn't break down. Now I really thought I had this thoroughly thought through and that I was erring on the side caution myself.

The guy turns around and tells me that nobody needs that much CFM for such a small space of 16-cubic feet... I do realize that I'm still here on the planet Earth. But I am not going to tightly seal up by little box anymore than worrying about light and bugs. When I am working on the final space I will re-use the parts of the small box, as I will use them to finish building my bigger area as the final stage.

Now he points out that I am still going to be using to high of CFM even for that, and the Carbon Filter and Fan will not work properly in such a small space as they are all rated for 700+ and my area will only be 224, that I'd be better off buy a 4-inch Can Fan and 4-Inch Carbon Filter, and then when I upgrade later just go to a 6-inch Can Fan and Carbon Filter. Because by oversizing it this much my Carbon Filter will not be able to properly scrub the air going through it even with a Fan Controller to dial down its speed.

He also tells me that ONLY a Can Fan is meant to be secured to a Carbon Filter, and that the Inline Fans are only for intakes and moving air when not being put under static pressure. Further that I have to size my Carbon Filter as closely to the Can Fan as possible, which is why they sell the Carbon Filters and Can Fans they do as they are sized up with one another per manufacturer's specifications.

I'll be the first to admit the last time I saw or deal with an Inline fan they were galvanized and typically used in HVAC applications. Can Fans were what you used with Carbon Filters, so I am not really in any position to argue about Fan types with him or anyone else, I simply just do not know and am having trouble finding that information.

As far as matching a Fan to a Carbon Filter, I know not to oversize your fan to your Carbon Filter and don't use a 4-inch Fan on an 8-inch Carbon Filter. But some Carbon Filters have 2 to 2.5-inches of depth (width) of carbon in the filtering area; so how can getting a filter that is longer be a problem? I mean it's more carbon to filter the same CFM and no increase in resistance since it is in length not in width which are said to be the best filters.

Then I am utterly confused how slowing down my fan so it is both quieter and draws less power a problem when slowing it down means that I will be pulling less CFM's across the carbon, but when I need to speed it up to move more air for whatever reasoning for smell or whatever else should be a good thing, right?

I mean sure you may not typically want to exchange all the air in a room 3-4 times every minute, but I can definitely think of times I wish there was more air movement and used fans to try to make that happen with open windows.

Can Fan is used for ?
Inline Fan should be used for ?
CFM, Fan Speed, and using a Fan Control to turn it down...
Too much of a Carbon Filter and it doesn't work? Really?
What am I missing, don't know, or just flat out am not understanding here?


Nug of the Year: 2016 - Member of the Month: Sept 2015, Nov 2016 - Nug of the Month: Oct 2016 - Plant of the Month: May 2016 - Photo of the Month: Nov 2020
Well piggy that was a long read and I wish I could answer more of your questions. But I've used the same old fan forever so this is one area in which I haven't been forced to look around much. It's completely unmarked so I know nothing about it, though it's obvious it's about twice as big as I need. I have no speed controller. I don't know why things are this way. I'm guessing that fans are built to run at a comfortable efficient speed, but growers are willing to sacrifice efficiency for reduced noise.
As long as your fan has enough power to deal with sucking air through the filter, then I think it's just a matter of physically joining the fan to the filter. You should be able to connect them using ducting or stove pipe fittings. You may need increasers or decreasers to adjust sizes and attach the two. Small gaps can be dealt with using weatherstripping, caulking, rubber, etc. Hose clamps and metal screws to finish. That's all totally possible.
As for having a huge fan attached to the tiny grow- I can't think of why not even though it seems a bit strange. But there might be something I don't know. There are a lot of things I don't know.
However- this forum is full of ridiculous things that get posted as ' the guy at the hydro shop told me blah blah blah...'. So all is possible.


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Well I am a person who doesn't settle for things I do not know the "right and true" answer too... In my quest to go dig up this information, I came across the company "canfilters" and in their FAQS section, I can honestly say I learned some new things. I have always thought it was wrong when people attach the - Carbon Filter - Hose - Light - Fan - Exhaust = Well I can finally say I can prove what I always thought was wrong, according to the makers of Inline & Can Fans, the Fan SHOULD COME BEFORE THE LIGHT... So that the Fan is positively pressurizing the light, and moving the most amount of air across the light to keep it cool. They cover making angels in duct, flex duct, and even how much air loss there is by using a carbon filter at the fan... I mean they tell you almost everything you want to know... But they do not say a single word in relations to what I am trying to find out... Ahh the frustration...

But I am not about to give up, if in doubt call the manufacturer about your question, get them to connect you to the tech guy and let him tell you... Then you can't argue he's wrong, because he's gone to school for it and he is more than likely the person or one of the persons who designed the thing and did all the testing on it to get the answer(s). Guess which guy I am at work 420 Magazine ® ? There is a reason I know this stuff and why doing it right is so important to me... but hey I will come back here and share what I learn with everyone else...

Not helping my frustration today I can't get a Nutrient Tank without paying an outrageous price for shipping... and on top of that they have a new design that just came out, everyone is trying to get rid of the old design, but nobody can tell you what is different between the two designs, other than one is new and lids don't fit properly between the two styles... Then there is a Black one and a White one, and a serious price difference for the white one, and again they aren't sure why the black one costs so much less... I think the white one is virgin ABS material and so it is much stronger, but I'm guessing the black one is ABS regrind and not as strong, hence why they dye it black to hide the different colors of the ABS regrind. I am calling the manufacturer of that as well.

Dr Fish

Well-Known Member
Piggy, sorry to hear about the divorce, if i'm wrong in assuming that, don't take offence.. It just reminded me of the time i came home and everything including the curtains were gone... Only a woman would take curtains......
If you bought abs sheet from a distributor you'll find the price difference about .65 cents a square ft more for one sheet of 8'x4' x 1/8" white abs.... Less if you buy more, up to a point... Manufactures use the same data sheets for regrind black as they do for uncapped virgin white.... It seems there's no difference in strength or at least none to speak of.... You could get lucky, but i've found manufacturers are almost never willing to talk to customers who buy retail from distributors ... Order 2'000 pounds and they'll talk as long as you want..... Some people buy white because they assume if it's white, it's better... It's not, it's just white... Why does it cost more? Because it's white...
I use black regrind abs and don't find any short comings with the strength.. After vacuum forming, slight imperfections on the inside give it away as regrind.... That's about all i got on abs.....
You should start with a little taller ceiling... The light will always need to be moved higher, plus the distance from the plant to the light.... Start with it the same height as your long term dream grow room... The most important thing is that you don't let planing the finished product stop you from starting.... Buy a light and plan around it... You can worry about what you'll need for the finished room as you need it...


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Actually Dr Fish, of all things I've been divorced, and she never took anything I had to throw out what she left behind, it was't even a woman, it was a so called male 'friend' of mine who felt that he needed everything I owned more than I did. He believed that my ability to grow plants laid in the books I owned, the equipment I had, etc... Why did he take everything else then? All I have ever known is that his girlfriend had shown up with him and that they sold everything of mine over a few months for money when they couldn't make it work. Chalk it up to a hard lesson learned, and a great chance to start over this time using only the best quality products that I know work.

I do pride myself in being charismatic, and being able to get to the bottom of information with companies... I spoke with them over at "Can Filters" and not surprisingly they didn't know there was a difference in Fans other than just a person choice. Yes the Can Fan is typically more powerful to move more CFM because of its design, but the Inline Fan are a slimmer design which yes more people do use for lights, bringing in air, and even filtering air from the carbon filter. Its really more of a question about space and preference they told me. So at least now that question has been answered by a long time trusted manufacturer...

As far as the Carbon Filter goes, by going with a larger than needed filter as long as I have the space for it the theory is that I'd have the potential to make it last longer, depending on of course the amount of air I move through it and how dirty the air environment for it is as well. They agreed with me a Fan Controller would be a great way to go, and of course point out that a Fan should never be slowed down more than 30% of its output, but they recommend 40%-50% to ensure that people do not underclock the fan leading to over heating of the fan. But it is better to have more power you are not using than find yourself in a position where you need more power and you just don't have it.

Thus in the end it proves what I was thinking since dealing with that guy at the Hydro Store, he just doesn't have a clue as to what he's doing. Most places I deal with know their products intimately and the person you speak with can tell you from their experience of this product or one similar to it, and not one time did this sales guy ever make mention of having used any of the products or something similar. A nice lesson learned though, as I continue my journey of shopping, planning and bringing my plan together in the end.
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