Drawing No. EH–TH–005 // Thermal Engineering & HVAC
Condensate Return Savings Calculator
Reviewed August 2026
Find the fuel energy and cost saved by returning hot condensate to the boiler feedwater system instead of replacing it entirely with cold makeup water.
What problem does this solve?
Steam condensate returns from process equipment already carrying significant sensible heat — often 80–100°C — compared to cold makeup water, which might be 10–15°C. Returning that hot condensate to the boiler feedwater system instead of dumping it means the boiler needs less fuel to reheat feedwater back up to steam temperature.
Inputs
Results
Background
Q [kW] = mass flow [kg/s] × cp,water (≈4.186 kJ/kg·K) × (Tcondensate − Tmakeup). This is the sensible heat already present in the returned condensate that the boiler doesn't need to add back by burning fuel.
Fuel input saved = heat energy saved / boiler efficiency, since the boiler itself is not 100% efficient at converting fuel into useful feedwater heating — the same efficiency that applies to normal boiler firing also applies to the fuel that would otherwise be needed to replace this heat.
Beyond the thermal savings calculated here, condensate return also typically reduces make-up water purchase and treatment chemical costs, and reduces the mineral/scale load entering the boiler (since condensate is essentially distilled water) — real-world savings from a condensate return project are usually larger than the thermal-only figure shown.
Frequently asked questions
Practical questions about inputs, assumptions and interpretation.
Because condensate already carries substantial sensible heat that would otherwise be wasted if dumped to drain, returning it directly reduces boiler fuel demand with no process change required — it's frequently one of the fastest-payback efficiency measures available in a steam system, especially where condensate is currently being discarded rather than returned.
This calculator assumes the full entered flow rate is returned; if only a fraction can realistically be recovered (due to venting losses, contamination risk in certain processes, or distance from the boiler), enter that reduced effective flow rate instead of the total condensate generated.
Yes, for a fixed flow rate and makeup temperature — the temperature difference term is directly proportional to savings. This is part of why minimizing flash steam losses (which occur when hot condensate is depressurized) and insulating condensate return lines both help preserve more of that returned heat.