# Boiler heat recovery

Recovering heat from flue gas and hot water around boilers.

Source page: https://www.materialinsights.org/energy/e_boiler_recovery/

Recovery and reuse · Heat to heat · No. 122

- Recovery and reuse
- Heat grade: Medium and low
 Recovery and reuse · Heat to heat · Foundation · Energy

Cool a boiler's flue gas by just 22 C and it gets one point more efficient, using heat already paid for.

Chart: Illustration: Boiler heat recovery

##### Where it comes from

Chart: Map of where it comes from

Boilers leak heat three ways: hot flue gas at 230 to 480 C, hot blowdown water and hot condensate. All can warm the cold feedwater arriving at 10 to 15 C right next door.

##### Three things to know

1. Cooling flue gas from about 230 C to 41 C can lift a boiler from 80% to 95% efficiency, by condensing its water vapour.
2. Below about 121 C, natural gas flue gas starts dripping acid, so condensing units need stainless steel.
3. Returned condensate still holds more than 10% of the steam's energy, plus water already treated.

##### The journey

1. 1 **Boiler leaks**Hot flue gas, blowdown and condensate
2. 2 **Economiser**Flue gas warms incoming feedwater
3. 3 **Condenser**Recovers latent heat from water vapour
4. 4 **Water loop**Condensate and blowdown heat returned
5. 5 **Less fuel**Same steam from a smaller flame

##### Go deeper pick a tab to open it in full

## Other sections

- [Overview](https://www.materialinsights.org/energy/e_boiler_recovery/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_boiler_recovery/correlation/index.md)
- [Science and thermodynamics](https://www.materialinsights.org/energy/e_boiler_recovery/rc-sci/index.md)
- [Engineering and integration](https://www.materialinsights.org/energy/e_boiler_recovery/rc-eng/index.md)
- [Economics and contracts](https://www.materialinsights.org/energy/e_boiler_recovery/rc-econ/index.md)
- [Impact and additionality](https://www.materialinsights.org/energy/e_boiler_recovery/rc-impact/index.md)
- [What to track](https://www.materialinsights.org/energy/e_boiler_recovery/tracking/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_boiler_recovery/links/index.md)