Can Filters

I had a wicked odor problem with my first grow, which I just finished up a few weeks ago. I have my second batch of plants going in a grow tent in my closet right now. They are just now starting to put off a little smell. I already bought a 4" inline fan. I am just looking for a filter now. From everything I've read Can filters sound like they are the best. I can't risk getting caught so I guess I need to shell out the money for one. If I'm not mistaken they have two different 4" filters and that is the 2600 and 9000 models. Here is a link to the 9000 which I am thinking about getting
CF Group :: Canfan, Canfilter

Then there is the 38 Special, which I'm assuming is a better filter that takes less contact time with the filter so you can run more air through it. Here is the link to that. CF Group :: Canfan, Canfilter

Does anybody have any experience with either of these? I have four plants in a 2x4 grow tent and I want pretty much any smell erased when it comes out of that tent. Is the 38 Special really worth the extra money? They cost quite a bit more. I think I can get the regular Can filter for $80 and the 38 Special one is more like $150. I would hate to spend a $100 on a filter that doesn't work, so if I need the 38 special I'll get it. I just want to make sure that I'm looking at the right model that I need and trying to figure out if it's worth the extra money to upgrade.

i got the 50 and it completely is eliminating ALL smell and it is over a year old. they work great and do the job, you just need to calculate your room size and go get the one that matches. i would definatly look at the dimensions and weight of the filter cause mine was bigger and way heavier than i expected. but if you do get an underrated combo for your room you will smell dank

Is there a calculation for sizing a room?

Yes there is and itâ??s really quite simple, all you need to do is take your cubic feet of the room (Length x Width x Height) and divide that number by the number of minutes you would like to exchange the air in the room (Only 1 â?? 3 Minutes is recommended) and that will give you the recommended minimum CFM that you need for that room, then you take that Min CFM number and match it to one of our filters and as long as that Minimum recommended CFM is higher then the exhaust minimum on the filter you will have adequate airflow and proper filtration for that room.

Cig - your basic calculation is correct but it is considerably more complicated than that. When sizing you have to account for additional drag on the fan. So add this to your calculation: x 1.3 due to the drag of the filter. x 10% for each foot of duct. x 1.5 for any 90 degree elbows. And that doesn't account for any cooling duties that fan must pull. Here is a walk through lifted from the sticky you can find in my signature line on grow room setup. It assumes air exchanged every 4 minutes. 3 - 5 minutes is what you want to aim for:

4x4x6 room = 96 CF. Divided by 4 minutes is 24 CFM required.
24 CFM + 130% ( 10% x 13' of duct) = 55.2 CFM
(55 CFM x 1.5) x 1.5 = 124 CFM (to allow for our two 90 degree bends)
124 CFM x 1.3 (to allow for air velocity lost to the filter) = 161 CFM.

To consider cooling duties add this:

For a 250HPS / multiply by .75
For a 400 / multiply by 1
For a 600 / multiply by 1.3
For a 1000 / multiply by 1.6.

I've done a ton of reading on filters. It is my only real concern. I've found that Mountain Air filters get top reviews consistently. They are rated to last longer at 3 years but they also come at a premium. I'm looking at one that will fit my 340 CFM fan for $205, although I could probably find it a bit cheaper online. My preference is to buy supplies locally in cash... Can fans do well, so do Phresh. My thinking is that you will be fine with most of them. When sizing, over size rather than under size. If you under size you will have oder. If you over size the filter will last longer. You decide!

This is the fan I got HydroFarm: Active Air 4â?� In-Line Duct Fan 165 CFM [eco-5600A] - Fans, Blowers & Ducting - Environmental Control - Discount Specialty Farm, Greenhouse & Garden Supply Store - Horticulture Source
It is 165 CFM. I just ordered the speed control for it because it is too loud when its running full throttle.
If you look at the filter ratings at Can's website it has Recirculating CFM and Exhaust CFM. I just wanted to make sure, but doesn't the exhaust CFM rating apply if you are planning on just using a single pass through the filter. I have a grow tent, so I need the air to be odor free after it's first pass, even though the same air will likely get circulated back through the tent again. If that is right, then I think the 9000 would probably be enough at an exhaust CFM rating of 55 once I turn my fan down. I'm starting to think maybe I need to go bigger than that though. I think the next step up is the model 33 which has an exhaust CFM rating of 200, which would be way more than enough for my fan and what I'm doing.
Does that sound right? If it does my only question I have left is whether or not I should get the regular can filter or should I upgrade to the 38 Special.

I would not go with anything rated below the CFM of the fan. You may dial it back to 55 CFM but you may find that that does not meet your needs and that you have to run it at 75 CFM in which case the filter will not be able to keep up. The 38 special might be overkill. In my case I can not afford failure. I periodically have a room full of lawyers above my grow room so I'm spending a little extra cash for a little piece of mind!