Heater core issue?

I was wondering how to tell if the heater core is leaking or defective in my 67 Dart. I'm getting white smoke out of the fresh air intake in front and also inside the car. It doesn't smell like burning oil or wires (thankfully) and it increases with the fan on. Also getting a film on the inside windshield. This car hasent been driven in a lot of years seems like it doing the domino effect when I repair something. Thanks for the help.