Abstract: A low excess air burner having a venturi shaped insert in the burner housing to create an even air distribution across the burner throat opening. The venturi shaped insert is adjustable through a predetermined range of positions to control the flame shape and length at high loads and to trim the air flow at low loads. An offset or step in the burner throat creates a turbulent recirculation zone to stabilize the flame front and to hold ignition within the burner arch. A spinner defuser is provided at the open end of the burner housing to impart a rotary motion to the air to provide fuel air mixing and stabilizing of the flame front to aid ignition. Air inlets are surrounded with a housing and have a perforated plate shield covering them providing a smooth evenly distributed air supply to the burner housing. All fuel air mixing occurs at the open end of the burner and is contained in the refractory throat to eliminate premature ignition in the burner housing.