Most new heaters have a 20 year or more warranty on the heat exchanger. Burners for gas heaters have also been redesigned as jet burners. There is a fan in the flue pipe now to assure clean, controlled combustion. When the heater shuts off, the controls allow the blower to run for a short time to get the last available heat out of the heater. Gas heaters are now controlled mostly via electronics.
All heaters have safety controls to guard against over-heating and something blocking the flue pipe.