[Alistair_N]

Hello all.

I have very recently found myself in a place where I can finally start working on my own grow. I've been reading up on here and elsewhere extensively for a while, getting my plans together, preparing for as perfect a DIY stealth micro I can pull off.

Stealth, of course, requires an appropriate filter, and here I am missing the one piece of the puzzle I still need: how to appropriately size said filter.

I've read all the lit on fan sizing, ventilation design, etc. I've studied the formulas and implemented them into my design. What I've not found is a formula for sizing a carbon filter vs. fan flow & pressure.

For example, something like:

% delta cfm = some function of [[fan mmh2o], [square area of filter], [depth of filter]]

Does that make sense? I'm really hoping to start my grow soon, but I'm not making a move until I feel confident my design will work, and I need this information. It needs to be so stealth my housemate will never know, so smell is the biggest worry.

Does anyone have any pointers, or a link to something I may have just missed? If any of you actually have such a formula, maybe include it in this thread and not just a link to it, so future searches can find it easy-like?

Thanks in advance.

The filter and the fan must be matched up. Drawing too much air or too little through the filter will not allow the filter to work correctly. That is why you want to purchase the correct size exhaust fan for your room first and match up the CFM rating on the filter to the fan.

[Alistair_N]

Originally Posted by tokinafaty420

The filter and the fan must be matched up. Drawing too much air or too little through the filter will not allow the filter to work correctly. That is why you want to purchase the correct size exhaust fan for your room first and match up the CFM rating on the filter to the fan.

Yeah, that I know. Which is good, for a pre-fab filter. I need to build my own, for space reasons. I want to know how to get that CFM rating based on the things I listed.

And obviously every filter is different, the only way to know for sure is to build and test. But there's got to be an approximation rule to use as a guide.

Originally Posted by Alistair_N

Yeah, that I know. Which is good, for a pre-fab filter. I need to build my own, for space reasons. I want to know how to get that CFM rating based on the things I listed.

Copy the size from the professionals. They already did all the research work for you. A 265 CFM can filter is about the size of a 5 gallon water bottle.

Hard to say it depends on the material used to build the filter. Inner wall, outer wall, liners, dust filter the carbon itself and how well its packed in the filter. I would build a filter larger than what I need with an oversize fan and use a speed regulator on the fan and set it where it works best. A lot of ifs.

[Alistair_N]

Originally Posted by tokinafaty420

Copy the size from the professionals. They already did all the research work for you. A 265 CFM can filter is about the size of a 5 gallon water bottle.

Alright.

So, let's say for example I have a fairly small PC-type fan of 50cfm. My space is pretty small, maybe 5cu.ft. Obviously, that's 10 changes per minute unobstructed. The lowest I'll want to go is 1 change/min, max maybe 3, so I want to end up with modified cfm between 5 and 15. I'll be able to determine lossage from my ventilation design easily enough, but I have no way to know how much a filter of a specific size will reduce CFM given a certain static pressure.

I'm wondering if anyone has the nitty-gritty on this, or has done/knows of any work to spec out a rough formula.

Knowing what a prefab filter's CFM rating is can be helpful if I just want to match up a standard blower, but if I want to design a system with unconventional parts with the least trial-and-error, it's exceptionally nice to have some math behind it.

And of course there is a lot of 'ifs,' I'm not looking for hard math.

Maybe this just isn't something that has been done yet? Per tokinafaty420's suggestion I am looking at prefab filters and the recommend CFMs and trying to see if I can work something out from that.

Originally Posted by Alistair_N

Alright.

So, let's say for example I have a fairly small PC-type fan of 50cfm. My space is pretty small, maybe 5cu.ft. Obviously, that's 10 changes per minute unobstructed. The lowest I'll want to go is 1 change/min, max maybe 3, so I want to end up with modified cfm between 5 and 15. I'll be able to determine lossage from my ventilation design easily enough, but I have no way to know how much a filter of a specific size will reduce CFM given a certain static pressure.

I'm wondering if anyone has the nitty-gritty on this, or has done/knows of any work to spec out a rough formula.

Knowing what a prefab filter's CFM rating is can be helpful if I just want to match up a standard blower, but if I want to design a system with unconventional parts with the least trial-and-error, it's exceptionally nice to have some math behind it.

And of course there is a lot of 'ifs,' I'm not looking for hard math.

Maybe this just isn't something that has been done yet? Per tokinafaty420's suggestion I am looking at prefab filters and the recommend CFMs and trying to see if I can work something out from that.

Good initiative, but you seem to be overthinking this. Just get large enough exhaust fan(s) and a speed regulator. 1 intake fan 80mm and 2 120mm exhaust fans to be sure that it can pull enough air through the filter, silently..

For micro grows there are several solutions for DIY scrubbers. To get a formula of any value you have to standardize on type first of all

[Jaybird2203]

This is abit old but I'm going to STRONGLY recommend you read Redgreenery's Ventilation 101 thread below

https://www.icmag.com/ic/showthread.php?t=112862

[gdbud]

Take a look at DIY - Build a Carbon Scrubber For Dummies!

[Pyramid]

The problem with PC fans is they dont work as well when there is a static pressure situation like with a carbon filter. They only pull when unobstructed. If you use a pc fan the most you can really put in front of it is a carbon sheet filter for and air purifier or something really small like 1/5 inch of carbon bed