Which two factors influence the effectiveness of a stack's draft?

The effectiveness of a stack's draft is primarily influenced by the diameter and height of the stack. Height plays a crucial role because a taller stack can create a greater draft due to the increased difference in temperature between the hot gases inside the stack and the cooler ambient air outside. This height allows for better dispersion of the exhaust gases, which helps ensure that they are effectively removed from the system.

The diameter is equally important because it affects the flow rate of the gases. A larger diameter allows for greater gas volume to escape, which can enhance draft performance. Conversely, if the stack is too narrow, it might restrict the gas flow, leading to insufficient draft and potentially causing issues like backpressure or poor combustion efficiency.

While temperature and pressure within the furnace are factors that impact the combustion process, they are less directly involved with how the stack itself creates draft. Similarly, the size of the fan and type of fuel may influence the overall system performance but do not have a direct impact on the fundamental characteristics of the stack that determine draft effectiveness. Thus, focusing on the diameter and height provides a clearer understanding of the mechanics involved in stack draft efficiency.