inches above vtl amps

Does anybody know what's the minimum distance I can safely leave above my vtl 450 watts amps (they're caged)?
VAC states 3" min. for their amps. That would give you something to go by. I'm pretty sure that is for an open shelf type rack, not a cabinet.
Post your question on Audio Asylum. Luke Manley of VTL answers questions regarding his products from time to time.
I went 5 1/2 from the top of the amps to the bottom of the shelf. See my systems for photo. I also installed a fan to blow across the amps during crazy concert sessions as a precaution, otherwise its not needed. It been like this for a few years now and no issues. The shelf does not feel hot.
Ask Joe Fratus from Art Audio.