Q: I had smoke come out my passenger side vents.

My drive to work is 20 minutes. After driving with the heat on 3/4 power with the heat turned up all the way. 4-5 minutes had passed and i started to smell burning rubber. I thought it was just coming from a car in front of me. So i ignored and kept driving and got on the highway, after probably another 10 minutes, the smell still stayed and worsened. After coming to a complete stop after getting off the highway i accelerated back up to about 20 mph, and thin/thick smoke started to come out the vents. i quickly pulled over and turned off the air and opened the windows. I popped the hood and seen nothing wrong, my coolant level was good and couldn't see anything physically wrong. The car was off after i pulled it over. After checking to see if anything was i turned the car back on and proceeded to go to work. I am curious as to what i can do to fix this problem or what you think the problem is. I have not used the heat again other than to see if the smell is gone in which it isn't.

My car has 39000 miles.
My car has an automatic transmission.