The heat capacity of flue gas is calculated based on the firing rate, stoichiometric air requirement, excess air, flue gas temperature, and fuel heating value. An empirical factor of 0.021 is applied to account for the specific heat properties of typical flue gas compositions.

\begin{equation}\label{eq:air-heating-exhaust-heat-capacity-flue} C_{flue} = \frac{Q_{fire} \cdot 10^6 \cdot \left(\frac{(1 + EA) \cdot A_{stoich}}{32} + 1\right) \cdot T_{flue}}{HV_{fuel} \cdot 1000} \cdot 0.021\end{equation}

Symbols

\(C_{flue}\)	Heat capacity of flue gas \([\unit{ \btu\per\degreeFahrenheit}]\)
\(Q_{fire}\)	Firing rate \([\unit{ \mega\btu\per\hour}]\)
\(EA\)	Excess air fraction \([\unit{ \unitless}]\)
\(A_{stoich}\)	Stoichiometric air requirement (gas) \([\unit{ \cubicFoot\per\cubicFoot}]\)
\(A_{stoich}\)	Stoichiometric air requirement (solid/liquid) \([\unit{ \pound\per\pound}]\)
\(T_{flue}\)	Flue gas temperature \([\unit{ \degreeFahrenheit}]\)
\(HV_{fuel}\)	Fuel heating value (gas) \([\unit{ \btu\per\cubicFoot}]\)
\(HV_{fuel}\)	Fuel heating value (solid/liquid) \([\unit{ \btu\per\pound}]\)
\(0.021\)	Empirical factor for flue gas heat capacity \([\unit{ \unitless}]\)
\(32\)	Empirical divisor for stoichiometric air calculation \([\unit{ \unitless}]\)