This setup involves a hot tank and a cold tank of gasses, which are then mixed to achieve a target temperature and pumped in to achieve the target pressure.  On most worlds maintaining a cold tank is quite easy (because the atmosphere on most worlds is below the temperature needed to smelt ore).  Maintaining a hot tank is a little trickier, and either involves a lot of energy spent on [[Pipe Heater]]s, or an auxiliary furnace to combust fuel and pipe the exhaust into an insulated tank. Another easier option is to have the entire setup, furnace, pipes and tanks, in an enclosed vacuum chamber, so heat remains in the gases. Note that the outside atmosphere on worlds with no air doesn't count, it must be an enclosed chamber with all air pumped out