98 Sportage Overheating in Heater

My car overheated inside the car, spraying hot water all over my feet and on the passenger floorboard with massive amounts of steam coming from all the vents. Is it the heater core or a vent hose?

From the experience of others, obviously your heater core is shot. YOu can alleviate the problem, temporarily, by uncapping the radiator..that is loosen the cap to the first stop. Not practical if external temperature is high though.
I'll find former pthreads that describe the core changeover ....forget the kia manual that calls for emptying the a/c....ahh..ok, I had made a copy:
www.avigex.ca/kia/heatercorereplacement.pdf