EngineerHub.orgWhat this calculator does
Uses steam and feedwater enthalpy difference to calculate useful duty, then applies boiler efficiency to estimate fuel input and annual consumption.
Inputs
Results
Worked example: 10 t/h natural-gas steam boiler
Step-by-step interpretation using the calculator's default inputs.
Assume a boiler produces 10 t/h of steam with steam enthalpy of 2778 kJ/kg, feedwater enthalpy of 419 kJ/kg, boiler efficiency of 85%, fuel LHV of 42.5 MJ/kg, 3% blowdown, 8000 operating hours per year, and a fuel price of 10 currency/GJ.
10 t/h = 10,000 kg/h = 2.778 kg/s.
Q = ṁ × (hsteam − hfeedwater) = 2.778 × (2778 − 419) ≈ 6.55 MW.
Fuel input = 6.55 / 0.85 ≈ 7.71 MW. This is the required fuel-energy input on the same LHV basis as the entered efficiency.
Fuel flow = 7.71 MW / 42.5 MJ/kg ≈ 0.181 kg/s, or about 653 kg/h.
With 3% blowdown, feedwater flow = 10 × (1 + 0.03) = 10.30 t/h.
At 8000 h/year, annual fuel energy is about 222,024 GJ/year. At 10 currency/GJ, the annual fuel cost is approximately 2.22 million currency/year.
Background
Optional reading — open any section below.
The useful duty is ṁsteam × (hsteam − hfeedwater). Enthalpies should come from a reliable steam-property source at the actual pressure, temperature and feedwater state.
Efficiency must use the same basis as fuel heating value. Mixing HHV efficiency with LHV fuel value gives an inconsistent result.
The page does not calculate stack losses, radiation losses, economizer performance, deaerator steam, startup fuel, combustion air, emissions or detailed blowdown energy recovery.
Frequently Asked Questions
Practical questions about assumptions, inputs and limitations.
The default model is for steam production. A hot-water boiler can be represented by using outlet and inlet water enthalpies, but a dedicated water-heating calculator may be clearer.
Use recognized steam tables or IAPWS-based software for the actual state. Do not assume one enthalpy for every pressure and temperature.
The displayed useful duty is based on steam only. Blowdown is used for feedwater mass flow, not a separate blowdown enthalpy loss; detailed efficiency calculations should include it explicitly.