Sums the heat input and both air corrections to determine the available heat for the process, for both current and improved conditions. Available heat represents the fraction of input energy that is actually usable for the process.

\begin{equation}\label{eq:pheic-available-heat} AH = HI + AC + CAC\end{equation}

\(AH\)	Available heat \([\unit{ \percent}]\)
\(HI\)	Heat input \([\unit{ \percent}]\)
\(AC\)	Air correction \([\unit{ \btu}]\)
\(CAC\)	Combustion air correction \([\unit{ \btu}]\)