[nonovurbizniz]

Could be a clog anywhere. so ya it could be the heater core.

Im not sure what your saying with the second part... the foggin up just means there is too much moister in the car so it condenses on the windows... if you put something to absorb the water in the air that should go away.

if you honda has a/c the condesor will pull out all excess moisture in the air. (ie it clears you fogged windows in a couple of seconds)