Heat output of subs question please

I'm looking at sinking a Paradigm servo sub(1200w rms/4500 peak) into a cabinet and am trying to figure out how large of openings I need for ventilation. I know how much a 1200 watt power amp puts out, but that is class a/b and the sub amp is class d. Does the class make a heat output difference? The sub is for movies only. I want to stay away from fans. Thanks!