It's mostly heat removal - I'm sucking in outside air to cool.  I'm mining in my garage, and pre-hood ambient temps ranged from +15-20 over outdoor temps.  

I threw the wooden hood together from scraps of OSB in the workshop, even the screws are reused.  It's got a 6"x12" furnace vent box on it that feeds into 6" ducting.  There's a 400cfm in-line blower sucking the hot air out.

It's changed the difference (so far) to about +10 over outdoor temps.  Yesterday it kept the garage cozy at 80*F, outdoor temps were 70*F.

Today we jumped up to 82*F outside and I rose up to 90*F ambient, I did forget to crank the blower up to 100% though, I'll try again tomorrow.

Without the hood I would have been above 100+F.  I'd need more CFM and possibly 8" duct to remove 3500watts (12000btu), that's if it was all in a sealed cabinet.

I'd call it functional, but a band-aid on what is ultimately my problem - heat leakage into the environment combined with not enough fresh air coming in to offset the inefficiencies.  

When my other ants come, I'll try to seal it up a little better, but the total cost was $12 for the vent box and about 30 mins of assembly - not a miracle, but a small win so I'll take it.