Abstract: A shift reactor is disclosed that is mounted on the exhaust end of an underoxidized burner so that the exhaust product is introduced to a cooler water bath in a compartment of the reactor. The exhaust product is passed through the water bath via submerged gas diffusers. The reactor compartment includes a collection chamber for receiving the bathed exhaust product containing hydrogen gas which is then exited to a shift catalyst chamber. The latter includes eductor for recirculation. A conduit may be coupled to the water bath for distributing heated water from the bath for exterior heating purposes or for purification means. A drain is operably connected to the conduit for permitting removal of excess water and a fill inlet is provided for adding water.