My growbox is 35CF. Im going to build this carbon filter

Ryoko Builds a DIY Activated Carbon Filter - 30 Minutes, $30 Dollars - The Garden's Cure

how strong of a fan should i use if that is going to be the only exhaust?

sorry that just looks a waste of time to me, those filters u get in in hepa filters and dehumidifiers, if they are the same as in the uk contain only a tiny amount of activated carbon, yr plants odour particles will saturate that amount of carbon in no time. U'd be constantly buying filters every couple of weeks, spending loads anyway. Y not get a proper filter the refillable type, they dont cost that much, and a fuck off bag of activated carbon and refil it every 12-18 months?? Ud be able to accurately match yr fan to the filter as u'l know all the flowrates etc?

I took a ten dollar bathroom exhaust fan from home depot, and some wire screen, five bucks, and a replacement pre-filter for humidifiers, made of charcoal, and it keeps the smell down to a manageable level. His method does work. Ive done it. I dont know about flowering though, I did this for veg, it was getting stinky.

i made one of those, and personally it was shit

it made a weird carbon/weed smell, really cut off airflow and just all in all i ended up having to buy 50 dollars worth of carbon alone to keep down the smell for it, i coulda used a store bought one and saved myself headaches

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those household bathroom fans just simply arent up to the job, they are only meant to run for a fraction of each day wired up to a thermostat humidistat or a light switch, not designed for 24/7 use, even the best branded household fans wil pretty soon fail under under 24/7 use. Why scrimp on your grow? Why not pay the extra initial outlay for made for purpose fans/filters and have the peace of mind that yr fan isnt gona fail in yr absence and u come home to dead plants, and know that yr smell is going to be dealt with properly! Your plants are yr babies man and u should be giving them the best possible environment for them to grow in and what you spend at the start wil be reaped back in yr first if not second harvest when u have everything dialled!

thank you monkeeman, i rest my case.

For those of you who vent your lamps, how many of you have an integrated lamp-cooling/room-exhaust fan, and who has a separate fan/duct for these tasks? I'm thinking about running a separate duct to cool the lamps, but I don't think I can afford TWO of those Hurricane fans.

Just want to let you know i have built those filters, they would ONLY be good for veg for about 3-4 weeks then they are quite useless, and i doubled the pads, spend $80 on a canfilter 33 that will actually work properly for a while in that small box

yes mate i run a 600w hps in a cooltube using only 1 fan/filter to cool my lamp and vent my room, was told it wouldnt work, but it does, temps rarely go above 26 degrees c, and when i zip myself into the tent i can feel plenty of fresh cool air being drawn in from the passive intakes. As long as you keep yr ductwork as short as possible, keep any bends or turns in the duct minimal. and use insulated/sound proof/sonoduct ducting after the cooltube because standard duct can get quite warm from the heat being blown thru the tube and without the insulated duct it will heat yr room further. Heres my c/filter/fan/cooltube setup.

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This Really depends on the size of room, how many lights. Cooltubes are great because they have minimal airflow restrictions. I wouldnt recommend this for everyone, But if you can make it work for you than go for it.

Also hit up your local hydro shop, ask about used gear, they are usually a goldmine of cheap used equipment, I got my 3500 cfm centrifugal blower for $60 and they retail for like $400