Firebox boiler with reduced temperature variation

A boiler comprising:

• a firebox comprising right and left side water walls and front and rear end water walls enclosing a combustion chamber, and connected at ends thereof such that water can circulate through the end and side water walls;
• a boiler shell mounted above the firebox such that the boiler shell is in fluid communication with the side and end water walls and such that water in the boiler shell is heated by a burner in the firebox;
• an output port operatively connected to the boiler shell;
• a first water input port adjacent to a bottom of a central portion of a first water wall and a second water input port adjacent to a bottom of a central portion of an opposite second water wall;
• wherein circulating water flows out of the boiler through the output port, through a distribution network and back into the boiler through the first and second water input ports.

A boiler firebox comprising:

• a right side water wall comprising an right inner wall and a right outer wall;
• a left side water wall comprising an left inner wall and a left outer wall;
• a front end water wall comprising an arcuate front inner wall connected to a front end of the right inner wall and connected to a front end of the left inner wall, and curving outward from the front end of the right inner wall and then inward and connected to the front end of the left inner wall, and a front outer wall connected to the front end of the right outer wall and to the front end of the left outer wall;
• a rear end water wall comprising an arcuate rear inner wall connected to a rear end of the right inner wall and connected to a rear end of the left inner wall, and curving outward from the rear end of the right inner wall and then inward and connected to the rear end of the left inner wall, and a rear outer wall connected to the rear end of the right outer wall and to the rear end of the left outer wall;
• wherein the right, left, front, and rear inner walls enclose a combustion chamber, and wherein water can circulate through a water chamber formed between the inner and outer walls of the end and side water walls.