New grow box build. With pics.

grouch said:

I would ditch the intake fan and make sure the intake holes are big enough to supply enough air for the exhaust. If you have even a slight amount of positive air pressure you will smell it once you hit flowering.

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Yes, could make intakes passive and use all fans for exhaust. I have passively used vacuum cleaner hepa filters for intakes before. It took two of them but negative pressure must be achieved for the carbon filters to do their job. Props on your build, pretty fucking cool.