The emissions, efficiency, and combustion chamber conditions of the Rayburn Prince 76, a clean-burning, hand-fired coal heater developed by the British have been studied. It was desired to determine if the downdraft design of the Prince would lead to low emissions when operated on American coals.

Temperature and species concentrations were measured in the unit's secondary combustion chamber. Temperatures and gas residence times in the secondary combustion chamber were found to range from 440 to 1040°C and 15 to 40 ms, respectively. Little soot and volatile oxidation probably occurred in the chamber, due to the relatively low temperatures and short residence times.

The emissions and efficiency of the heater were determined for operation on two bituminous coals at both high and low firing rates. The CO, NO_x, SO_x, and smoke emission factors were found to range from 38 to 120 g/kg, 1.2 to 5.8 g/kg, 3.3 to 5.4 g/kg, and 2.3 to 16 g/kg, respectively. The smoke emission factors for the Prince were found to be up to six times lower than those found using identical coals in updraft stoves. The overall efficiency of the unit was determined to range from 54 to 60%. The sensible energy losses were found to represent the majority of the total energy losses.