FWIW I have my tubed amps on the bottom shelf of a cabinet. When used the doors in front of the amp is open. In the back of the cabinet I cut openings to accomodate two 120v fans wired in series. In that fashion they move lots of air, each fan at a lower speed. The fans draw the air over the amps and push it out the rear, The noise level is very low and not intrusive at all. After operating all day in about 6 cubic feet of space the amps are 'cool', relatively of course. You can get these fans at an electronics store for about $20 each plus some wire and a switch.