Its not that complicated  The extra harmonic power that they are generating is then filtered out correct  Yes  So the filters are dissipating a lot of heat  No People design the output filters of classD amplifiers so they dont dissipate heat  Passive electronic filters are made from  types of components resistors capacitors and inductors In theory capacitors and inductors do not dissipate any heat  only the resistors dissipate heat  So people who design classD output filters simply dont use any resistors Only capacitors and inductors  In practice real capacitors and inductors have some small amounts of parasitic resistance so classD output filters do get slighly warmer than room temperature Still the total heat generated by a classD amplifier and its filter is still far less than any linear amplifier with comparable output power  So where does this extra harmonic power go if it is not sent out to the speaker or dissipated in the output filter  It is temporarily stored in the filter in the capacitors and inductors At some instants energy flows into the filter charging the capacitors and ing the inductors At other instants energy flows backwards from the filter through the classD amplifier back into the power supply This is why classD amplifiers need a lot morebigger capacitors on their power supply than other classes