The flue gas volume is calculated using the firing rate, stoichiometric air volume, excess air, and fuel heating value.

\begin{equation}\label{eq:cascade-high-to-low-flue-volume} V_{flue} = \frac{F_{high} \cdot SAV_{high} \cdot (1 + EA_{high}) \cdot CF}{HV_{fuel}} + \frac{F_{high} \cdot CF}{HV_{fuel}}\end{equation}

Symbols

\(V_{flue}\)	Flue gas volume \([\unit{ \scf\per\hour}]\)
\(F_{high}\)	High-temperature process firing rate \([\unit{ \MMBtu\per\hour}]\)
\(SAV_{high}\)	Stoichiometric air volume \([\unit{ \scf\per\MMBtu}]\)
\(EA_{high}\)	Excess air (fraction) \([\unit{ \unitless}]\)
\(CF\)	Conversion factor (e.g., 1,000,000 for MMBtu) \([\unit{ \unitless}]\)
\(HV_{fuel}\)	Fuel heating value \([\unit{ \btu\per\scf}]\)