The energy saved in the boiler is calculated from the condensate returned to the boiler system. By returning hot condensate instead of using cold makeup water, less energy is needed to generate steam. The calculation multiplies the net steam flow (excluding bypass), the enthalpy difference between condensate and makeup water, and the operating hours, then divides by the boiler efficiency. The net steam flow accounts for the usable condensate that can be returned to the boiler.

\begin{equation}\label{eq:water-heating-steam-energy-saved-boiler} E_{saved,boiler} = \frac{(\dot{m}_{steam} - \dot{m}_{bypass}) \cdot (h_{s,out} - h_{makeup}) \cdot t_{op}}{\eta_{boiler}}\end{equation}

Symbols

\(E_{saved,boiler}\)	Annual energy saved in boiler \([\unit{ \kilo\joule\per\year}]\)
\(\dot{m}_{steam}\)	Steam mass flow rate \([\unit{ \kilogram\per\hour}]\)
\(\dot{m}_{bypass}\)	Bypass steam flow \([\unit{ \kilogram\per\hour}]\)
\(h_{s,out}\)	Outlet steam specific enthalpy (saturated liquid/condensate) \([\unit{ \kilo\joule\per\kilogram}]\)
\(h_{makeup}\)	Makeup water specific enthalpy \([\unit{ \kilo\joule\per\kilogram}]\)
\(t_{op}\)	Operating hours per year \([\unit{ \hour\per\year}]\)
\(\eta_{boiler}\)	Boiler efficiency (fraction) \([\unit{ \unitless}]\)