Calculates the effective heat input to the process for both current and improved conditions, using flue gas temperature and empirical coefficients. Heat input reflects the energy delivered to the system.

\begin{equation}\label{eq:pheic-heat-input} HI = H_B + H_C \cdot T_{FG}\end{equation}

\(HI\)	Heat input \([\unit{ \percent}]\)
\(H_B\)	Heat input base (95.0) \([\unit{ \percent}]\)
\(H_C\)	Heat input temp coeff (-0.025) \([\unit{ \percent\per\degreeFahrenheit}]\)
\(T_{FG}\)	Flue gas temperature \([\unit{ \degreeFahrenheit}]\)