Boiler with reduced NOX emission

An oil or gas burning boiler, comprising:

• an exterior housing;
• a water-cooled fire chamber within said exterior housing having a rear face wall;
• a door on said exterior housing, said door, when closed forming a front face wall of said fire chamber, said door being cooled by water circulating therein and having an opening therethrough for an oil or gas burner producing a flame;
• and
• a cylindrical insert having an opening therethrough, said insert surrounding the door opening and being secured to an inside of said door to project into said fire chamber so that the insert opening is essentially aligned with the door opening, said insert being cooled by the water circulating through said door and reducing a cross-sectional area of said fire chamber available for the flame over a portion of the length of said fire chamber.

A boiler, comprising:

• an exterior housing;
• a water-cooled fire chamber within said exterior housing and having a rear face wall;
• a door on said exterior housing, said door, when closed forming a front face wall of said fire chamber, said door being cooled by water circulating therein and having an opening therethrough for a burner producing a flame;
• and
• a water-cooled partition located in a rear portion of said fire chamber in front of the rear face wall for dividing the flame.