IIRC, you want a fan with CFM (cubic feet per minute) of three times the cubic feet of your grow cabinet.

Your cabinet's cubic feet are around 31 feet.

Therefore, 3*31=93 CFM should be the minimum rating of your exhaust fan.

Look into getting a squirrel cage fan with 100+ CFM. They are powerful and fairly compact. Durable, too.

You can also lookinto getting a hurricane fan as well, but I don't have any experience with those.
krustythfreakinclown Reviewed by krustythfreakinclown on . Would these fans do the job (400W HPS). Hey, Im planning on building a 5'6"H X 2'6"W X 2'4"L Grow box, im gonna use a 400W HPS light with a Sylvania bulb. Im planning on getting these and having one for active intake/blowing on plants and 1 for cooling the heat from the light. ---> http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=7617002059&sspagename=ADME%3AL%3ARTQ%3ACA%3A1&rd=1 Do you think theyed do the trick? Im also gonna make a Carbon filter for my exhaust. Rating: 5