I have a closet underneath the stairs in the basement that would be an ideal place for a hidden equipment rack. I could passively pull in cool air from (the large gap) under the closet door, but I do not know how to build an invisible duct to actively expel warm air. I do not want to vent into the garage through a flap because I don't want any sawdust from the garage to even have a chance of making it back into the closet. On the other hand, I do not see any places I could hide a vent into the house in the stairs or along any trim...

Any brilliant ideas? I can take pictures tonight if it would help.

Details of an invisible vent:

















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I would just do a 3 pronged attack with a silent in-line fan (fantech). Use an attic fan thermostat to control the fan.

A flap exhaust vent in the garage, a back draft damper with rubber gasket as shown connected to the intake grill and then put some filter media over the intake grill in the under-stair space. I doubt any significant dust could make it through the gauntlet

http://www.ntsupply.com/images/products/RSK6_2w.jpg

Invisible ink? ;)

Details of an invisible vent:

















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AVS club members can see the invisible vent diagram.

That's an incredible design, Jeff. Simple and eligent. Well done.