Abstract: A system for purifying a gas provided with an apparatus comprising a main container defining a substantially closed chamber, an intake fitting having an intake projecting from the chamber and having inside the chamber a filter element, an outlet fitting having an outlet projecting from the chamber offset from the intake and having inside the chamber a filter element offset from the filter element of the intake fitting, and means defining in the chamber an internally sealed well between the filters. A baffle is provided in the chamber between the filters so that gas passing between the filters is deflected by the baffle. A heater is provided in the well. An outer container surrounds the main container and defines a space therearound. This space is insulated, either by being filled with an insulating material or by being evacuated.