Building a heater into rear defroster blower hose

Bohica, Yea you're right, I should have said "should typically be designed" rather than "are designed".

You gave alot of detailed information about heating elements and fans . Is that information specifically accurate to the models of heaters I linked to? Sounds like some generalizations based on assumed design to me. Unless you have had those particular exact models apart and tested, you are only making educated speculation. Granted it sounds more educated than my speculation, so kudos to you Sir or Ma'am.