I AM SELLING A USED 4 CELL HEAT EXCHANGER FROM MY GOODMAN GMP 100-3 FURNACE. THE PART NUMBERÂ IS 2921306S. IT CAME OUT OF MY HOME FURNACE WHICH WAS WORKING PERFECTLY BUT I INSTALLED A MINI SPLIT MITSUBISHI A/C WITH HEATER SYSTEM SO I DIDN'T NEED THE FURNACE HEATER ANYMORE. I DECIDED TO SELL THE PARTS INSTEAD OF THE WHOLE FURNACE AS IT IS WORTH MORE AS PARTS, GO FIGURE!