High-efficiency heating apparatus

A deep fryer, comprising:

• a cooking vessel for holding a cooking medium, the cooking vessel comprising:
• a front wall;
• a rear wall;
• a bottom wall;
• and
• opposing side walls;
• and
• a natural draft combustion system comprising:
• at least one supply conduit for receiving and distributing a combustion gas;
• at least one burner in fluid communication with the at least one supply conduit;
• and
• at least one generally horizontal combustion chamber in fluid communication with the at least one burner, the combustion chamber forming a discrete enclosed chamber and being exterior to and in heat transfer communication with an exterior surface of one of the sidewalls;
• wherein each combustion chamber comprises:
• an inlet portion located near the front wall of the cooking vessel;
• and
• an outlet portion located near the back wall of the cooking vessel;
• wherein the combustion gas flows continuously in a generally horizontally orientation along a corresponding side wall of the cooking vessel from the inlet portion to the outlet portion;
• and
• wherein at least one of the combustion chambers is recessed into one of the side walls.