A method to produce AlF.sub.3 (20) from countercurrent contact of HF gas (18) and Al.sub.2O.sub.3.3H.sub.2O (16) solids in a reactor (9) generates reaction heat in the reactor, and where air (42) is used as a coolant in a cooling jacket (44) around the outside of the reactor to produce heated air (46), which heated air is combusted with natural gas (52) to provide combusted exhaust gas (58) which can be used as a heating agent.