Calculator
Boiler Blowdown Calculator
Calculate the required boiler blowdown rate based on feedwater TDS, boiler TDS limit, and steam flow. Estimate the energy and water cost of blowdown.
Interactive toolUpdated July 2026
Inputs
Typical: 3,000 ppm for low-pressure
Results
Blowdown Rate
7.1%
Of feedwater flow
Blowdown Flow
714.3 kg/hr
Hot water discharged
Makeup Water Required
10,714.3 kg/hr
Steam + blowdown
Energy in Blowdown
154.8 kW
Potential heat recovery
The Formula
Blowdown % = Feedwater TDS / (Boiler TDS Limit − Feedwater TDS) × 100
The key insight: lowering feedwater TDS (through better water treatment or more condensate return) reduces the blowdown requirement, saving both water and energy.
Energy Recovery
- Blowdown water contains approximately 780 kJ/kg of energy (at 10 bar g)
- A blowdown heat recovery system (flash tank + heat exchanger) can recover 50–80% of this energy
- The recovered heat preheats the feedwater, reducing boiler fuel consumption
- Typical payback for a blowdown heat recovery system: 1–2 years