On the hot air holding less oxygen: I have thought a lot about that. I think if you were using your blower to collect and blow hot air that would be the case, less oxygen. However, if you are blowing cold air with the blower then heating the air, it should make higher pressure, but once the air is in the pipe the oxygen percentage can't change, right? On the other hand diesel engines compress air with a turbo then blast it through an intercooler before blowing it into the engine, but they are happy to be without heat in that case...