Abstract: A coal-burning boiler wherein primary air is admitted in the boiler front, below the grate, and secondary air is admitted in the rear of the boiler, below a box-like baffle member. The baffle member is disposed parallel to the grate and divides the boiler into upper and lower chambers communicating adjacent the boiler front, whereby the streams of primary and secondary air merge to flow over both the lower and upper surfaces of the baffle prior to exiting the boiler by way of a stack at the rear thereof. Secondary combustion thus occurs along the lower or under surface of the baffle member. The baffle is subdivided by parallel, longitudinally extending members so as to define a single, continuous fluid flow channel, whereby water may be efficiently heated by passage therethrough. The boiler is formed of upper and lower halves bolted together along mating peripheral flanges.