They did not add heat, actually blew cold air, did an OK job of clearing the back window, if there were only 2 or less people in the car, but did make the back of your head cold. LOL
Seems to me they blow whatever the air temp in the passenger compartment up at the window. I always give any of my rigs a good 5 minute warm up so it seems it might be able to de fog the back window ok
