When the heat Is on I smell antifreeze, is it the heater core how do I know

Windows do get fogged over but have not seen water in floor yeyet

when mine went out,i had to wipe the inside of windshield 10 times a day,it was so bad.i had to run the a/c with the windows down in november to try and clear it up,and it was 18 degrees.you may try to back flush it both ways to see if you can get crap out of it.