i would go with one filter but a good filter so you have a 8*4 room and let's say 7 feet high that's 224 cubic feet. 224/5=44.8.i personally would not buy a filter from walmart but how many cfm are there rated for? i could not find 50 cfm filter so i would go with a 98cfm can filiter the smallest i see people selling
The ideal carbon filter for small rooms or chambers. The heavy-duty Can Filter 2600 successfully eliminates odors for up to 18 months.
Moving 94 cubic feet per minute, this carbon filter weighs approximately ten pounds.
Can Filter 2600 has a screw-on or snap-on mounting feature and comes with pre-filter and appropriate flange.
Compatible with any
4" inline fan or
Active Air Exhaust Fan 95CFM.
Only 18” tall with a diameter of 5.5”. (Dimensions include pre-filter).
Technical Specifications:
+ Max cfm: 42/71m³h @ 0.1 sec contact time
+ Pressure drop at Max. CFM: 42pa/ .20wg
+ Prefilter: Yes
+ Flange: 4"
+ Outside Diameter: 140mm/5.5" (with pre-filter)
+ Height: 453mm/18"
+ Total Weight: 4.5kg/9lbs.
+ Carbon Weight: 2.1kg/4.63lbs
Usually ships in 24 hours.
Price $89.00
@
http://www.bustan.ca/product_detail.asp?menuID=1&SID=14&PID=913
but you can go to your local hydroponics store which i would recommended
and then for inside where your growing get a ONA puck or spray for 20 bucks and will prevent any bad smell escaping when opening the door as a last line of odor defense
Also are the fabreeze filters charcoal?