Computes the radiated heat flux using the U.S. customary Stefan–Boltzmann constant and the emissivity of the outermost surface (jacket or bare tank wall).

\begin{equation}\label{eq:insulated-tank-radiation} q_{rad} = \sigma\,\varepsilon\,A\,(T_s^4 - T_\infty^4) \end{equation}

Symbols

\(q_{rad}\)	Radiative heat loss \([\unit{ \btu\per\hour}]\)
\(A\)	Lateral tank surface area ( \(\pi,d,H\)) \([\unit{ \foot\squared}]\)
\(\sigma\)	Stefan–Boltzmann constant (1.713441 × 10⁻⁹) \([\unit{ \btu\per\hour\foot\squared\degreeRankine\tothe{4}}]\)
\(\varepsilon\)	Surface emissivity (jacket or bare tank) \([\unit{ \unitless}]\)
\(T_s\)	Outer surface temperature (jacket or bare tank wall) \([\unit{ \degreeRankine}]\)
\(T_\infty\)	Ambient air temperature \([\unit{ \degreeRankine}]\)