The flow meter method uses the instantaneous gas flow rate reported by a flow meter together with a quantity multiplier (number of identical units), annual operating hours, and the Btu content of natural gas to obtain total annual energy use. The factor 1.03/1000 converts the product of flow rate (ft³/hour) and operating hours (hr/yr) to MMBtu/yr using the approximate higher heating value of natural gas.

\begin{equation}\label{eq:natural-gas-reduction-flow-meter} Q_{total} = \dot{V} \cdot k_{units} \cdot t_{op} \cdot \frac{1.03}{1000}\end{equation}

Symbols

\(Q_{total}\)	Annual natural gas energy use \([\unit{ \MMBtu\per\year}]\)
\(\dot{V}\)	Gas flow rate measured by the flow meter \([\unit{ \cubicFoot\per\hour}]\)
\(k_{units}\)	Quantity multiplier (number of identical units) \([\unit{ \unitless}]\)
\(t_{op}\)	Annual operating hours \([\unit{ \hour\per\year}]\)
\(1.03/1000\)	Btu content conversion factor for natural gas \([\unit{ \unitless}]\)