_____ stoves have three characteristics that assist in complete, clean combustion: pre-heated combustion air introduced from above the fuel; firebox insulation; and a large baffle.

Non-catalytic stoves are specifically designed to achieve efficient and complete combustion by incorporating features that optimize the burning process. The introduction of pre-heated combustion air from above the fuel helps to ensure that the fuel ignites thoroughly, leading to a more complete burning of the materials. This helps reduce the production of smoke and harmful emissions.

The insulation within the firebox plays a crucial role in maintaining high temperatures necessary for efficient combustion, which facilitates the breakdown of gases and smoke particles that would otherwise escape unburned. Additionally, the presence of a large baffle within these stoves helps to prolong the gases' travel time within the combustion chamber, allowing for more thorough mixing with the heated air, further enhancing combustion efficiency.

In contrast, catalytic stoves operate with a catalyst to improve combustion efficiency, while wood and pellet stoves may not feature the specific combination of characteristics mentioned in the question, leading to less efficient combustion.