An exhaust stack having a junction tube and a flue is provided. The flue has a silencer portion, a converging duct portion, a tubular portion, and a diverging diffuser portion. The silencer portion fluidly communicates with the junction tube. The silencer portion has a first hydraulic mean cross-sectional flow path, and the tubular portion has a second hydraulic mean cross-sectional flow path less than or equal to the first hydraulic mean cross-sectional flow path. The converging duct portion is coupled between the silencer portion and the tubular portion. The diverging diffuser portion is coupled to an end of the tubular portion opposite to the converging duct portion, such that exhaust gases flowing through the junction tube, the silencer portion, the converging duct portion, the tubular portion and the diverging diffuser portion have a reduced overall pressure drop, at least in part due to the diverging diffuser portion and the second hydraulic mean cross-sectional flow path being less than or equal to the first hydraulic mean cross-sectional flow path.