Boiler Economizer Heat Recovery Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 26, 2026Boiler Economizer Heat Recovery Calculator
An economizer cools flue gas on its way to the stack, recovering heat that has already been paid for in fuel rather than letting it vent to atmosphere - typically one of the most cost-effective boiler efficiency upgrades available.
Formula: Q = ṁ × cp × ΔT
Example: 8 kg/s of flue gas at 1.05 kJ/kgK specific heat cooled by 60K recovers 504 kW.
How to Use This Calculator
- Enter flue gas mass flow rate.
- Enter flue gas specific heat (roughly 1.0-1.1 kJ/kgK).
- Enter the flue gas temperature drop across the economizer.
Feed this recovered heat figure into the Boiler Feedwater Heating Duty Calculator to see what feedwater temperature rise it can support.