Today I have been having problems with misting up windscreen, when I put the heating on early this morning the windscreen misted up and there was a very fine layer of mist across the windscreen and the front side windows, I ended up putting the heater on full and on full heat, and had the same problem on the way home. The drive is around 100 miles round trip. The carpet does not feel damp and I check the coolant level this evening and it does not looked like it's dropped any but I am worried the heater core has a very small crack which could be dripping and causing the misting. Is there anything I can check, or should be looking for? Also is the heat exchanger a dash out job?