AMPs and A/V/R's require a good amount of ventilation, to keep them cool. ALWAYS err on the side of precaution. Add a small fan if necessary.
I just bought and installed a Onkyo TX-SR674. I have about 1.5 inches of clearence from the the top shelf which is glass. The botttom shelf has an additional inch. Will heat effect the preformance and life of my new reciever?