New 8” carbon filter problem


Hello all,

I recently bought a new 8” carbon filter for around $65 and attached to my 8” inline fan. After just one day my temps (even with the fan on high) went from 73f to over 84f so I removed the prefilter to see what that would do and maybe…maybe it reduced temps by 1 degree.
I’ve since ordered another carbon filter made by Phresh company. Was much more money but actually stated the CFM flow rating of the filter which is more than what my fan is rated at. It should be here tomorrow so I will be able to see the difference as I am in my second week of flowering and the smells are really getting well wonderful lol.
The “defective”? Filter will be sent back once I verify the new one is working as intended.
Has anyone else had issues with a new filter which seemed to severely reduce the CFM my guess by more than 50% just based on putting my hand over the outflow duct and feeling the flow.




What is your humidity like? Are you using a humidifier? I’ve heard of them drawing too much moisture into them and “clogging” up, could be that?


Thanks for the reply @elheffe702

My humidity is around 40. I have a humidifier but it isn’t running much now as I’m in flower with lower RH.
I went through the clogged prefilter deal with my 4” inline before I upgraded to the 8” inline so am aware of hard water and white dust issue with using a humidifier and clogging the prefilter.

The carbon filter was only used for 1 day when I realized the airflow was severely being restricted because of my increased temps When it was attached to the fan.
I tried it without the prefilter with hardly any gain in flow.
Only way to keep my temps below 80f is without the carbon filter attached.


Yeah, sounds like a bad one to me.


a carbon filter can reduce cfm by 25-50%,
if everything else is optimal it should only reduce it by 20-25%,
if other things r reducing air flow also, then a filter can reduce cfm by 50%+,

cheap fans and filters also have a larger drop in cfm,
i always advise to ‘buy good to great equipment’.!!

your new Phresh filter is great quality, it will perform as advertised.!!
Can-Filter is great also and i think is a little cheaper.!

Hurricane, Vortex, and Can-Fan i think r still great fans,
my 6" Hurricane SHO (630 cfm) has been used for 5 yrs and still running strong.!
this fan is actually 15 yrs old, i took a 10 yr break, and it has a white body,
Hurricane’s r black now.! lol


Thanks for the info @SlowOldGuy.
Recommendations based on long term use by someone stands above the rest in my opinion.
My fan isn’t one of those brands but was purchased at a quality multi store multi state grow store with a good rep and I hope to get a long life out of it as you have.

Thanks again



if u paid $200’ish, it is probably a good one.!

let us know about the new filter, might be other things to do to keep up the airflow.!!


Installed my Phresh new 8” carbon filter.
Rated for max airflow of about 745cfm which is more than my fan puts out!
Wow this thing rocks! Did not restrict my airflow at all!
I’m able to have the inline fan speed setting the same with or without the filter attached to hold the temps!
Boxed up the new old one for a refund.
I decided to weigh the 2 filters to see and the one that is being returned weighed 10lbs was 20” long
The Phresh weighed 22lbs and is 24” long


Great! I’m glad it wasn’t something more complicated. :v: