The total instantaneous heat loss is multiplied by annual operating hours and divided by a factor of 10 and the heating system efficiency to convert to the annual energy equivalent the heating system must supply.

\begin{equation}\label{eq:insulated-tank-annual} Q_{annual} = \frac{q_{total} \cdot t_{op}}{\eta} \end{equation}

Symbols

\(Q_{annual}\)	Annual heat loss (efficiency-adjusted) \([\unit{ \btu}]\)
\(q_{total}\)	Total instantaneous heat loss ( \(q_{cc} + q_{rad}\)) \([\unit{ \btu\per\hour}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)
\(\eta\)	Heating system efficiency (0–1) \([\unit{ \unitless}]\)