What Does This Boiler Fuel Consumption Calculator Do?
Fuel consumption is the amount of fuel your boiler burns to make a given amount of steam. It depends on steam flow, steam pressure and temperature, feedwater temperature, boiler efficiency and fuel GCV. If any of these change, fuel rate changes.
This calculator helps you estimate fuel rate in kg/h or Nm3/h for your system. It also gives heat output and heat input in kW, evaporation ratio and, if you enter fuel price, hourly and annual fuel cost. You can configure different fuels to compare gas vs oil vs biomass for same steam duty.
After you estimate fuel rate, you need to configure feedwater flow for that steam output. Our boiler feed pump calculation tool helps you size pump head and flow for the same duty, including blowdown and margins.
Boiler Fuel Consumption Formula
It is a heat balance. Useful heat in steam comes from fuel.
Fuel Consumption = Heat in Steam ÷ (GCV × Efficiency)
Q_out = m_steam × (h_steam − h_feedwater) [kJ/h]
m_fuel = Q_out ÷ (GCV × η) [kg/h or Nm³/h]
Evaporation Ratio = Steam Flow ÷ Fuel Flow
Cost per hour = m_fuel × Cost per unit
η is efficiency on GCV basis in decimal. GCV must be in same basis as fuel flow. For gas, GCV in kJ/Nm3 gives flow in Nm3/h. For oil or coal, GCV in kJ/kg gives flow in kg/h.
How to Use the Calculator
- Select fuel type. Natural gas, diesel, coal etc. It fills typical GCV but overwrite with lab value for accurate rate.
- Enter steam flow, pressure and feedwater temp. These set steam enthalpy and heat needed per kg steam.
- Set saturated or superheated. Keep saturated checked for most firetube boilers. Uncheck and enter temp if you have superheater.
- Enter boiler efficiency and GCV. Use tested efficiency if available, otherwise 88-90% for gas, 86-88% for oil, 82-85% for coal.
- Enter fuel cost and hours (optional). To estimate annual cost and consumption.
- Click Calculate Fuel Rate. Result appears only after click. Reset clears results.
Understanding the Results
Fuel Consumption Rate
Main result in kg/h for solid and liquid fuel, Nm3/h for gas. This is as-fired rate at your efficiency. If efficiency drops 2%, fuel rate goes up about 2.3%.
Heat Output and Heat Input
Heat output is useful heat in steam. Heat input is fuel heat including losses. Heat input divided by 9.81 gives equivalent boiler horsepower.
Evaporation Ratio
kg steam per kg fuel or per Nm3. Higher ratio means better fuel use. Track this daily to spot drift in your system.
Fuel Cost
If you enter cost per unit, you get cost per hour and per year. Useful to compare fuel switch or economizer payback.
Worked Example
Boiler makes 2000 kg/h saturated steam at 10 bar g, feedwater 85°C, efficiency 88% on GCV, natural gas GCV 35,500 kJ/Nm3, cost $0.55 per Nm3, 8000 h per year.
| Step | Calculation | Result |
|---|---|---|
| Feedwater enthalpy | 4.186 × 85 | 356 kJ/kg |
| Steam enthalpy hg at 10 bar | from tables | 2778 kJ/kg |
| Delta h | 2778 - 356 | 2422 kJ/kg |
| Heat output | 2000 × 2422 | 4,844,000 kJ/h = 1345 kW |
| Heat input | 1345 ÷ 0.88 | 1529 kW |
| Fuel rate | 5,504,000 kJ/h ÷ 35,500 | 155 Nm3/h |
| Cost per hour | 155 × 0.55 | $85.25 /h |
| Annual fuel | 155 × 8000 | 1,240,000 Nm3/year |
So you burn about 155 Nm3 per hour. If feedwater goes up to 105°C with economizer, delta h drops to 2338 kJ/kg and fuel rate drops to 149.5 Nm3/h - saving about 3.5% fuel.
What Values Should You Enter?
Steam Flow
Average flow at steady load. If no meter, use BHP × 15.65 kg/h for from and at estimate.
Steam Pressure
Operating pressure. Sets hg. Higher pressure slightly raises hg up to about 30 bar then drops.
Feedwater Temp
At boiler inlet or economizer inlet. Higher temp means less fuel per kg steam.
Boiler Efficiency
Use tested value on GCV. If not tested, use 88% gas, 86% oil, 82% coal as start and refine later.
Fuel GCV
Lab value for as-fired fuel. For gas, GCV varies with composition. For coal, moisture lowers usable GCV.
Fuel Cost
Cost per kg or per Nm3 at same basis as GCV. Leave zero if you only need rate, not cost.
Factors That Change Fuel Consumption Rate
Feedwater Temperature
Every 6°C rise in feedwater cuts fuel about 1%. Economizer and condensate return help most.
Boiler Efficiency
Low excess air, clean tubes and low stack temp keep efficiency high. 2% efficiency loss means 2% more fuel rate.
Steam Pressure and Superheat
Higher pressure or superheat raises hg, so more heat per kg and higher fuel rate per kg steam.
Blowdown Rate
Blowdown is extra water heated and dumped. 5% blowdown adds about 2-3% to fuel rate if heat not recovered.
Fuel Quality
Wet coal or biomass has lower usable GCV, so mass rate goes up even if energy rate same.
Load Factor
At low load efficiency drops and radiation loss share rises, so fuel per kg steam goes up.
Common Mistakes
- Mixing GCV and NCV: Using NCV with GCV efficiency makes fuel rate look 8-10% low for gas.
- Ignoring feedwater enthalpy: Some use hg only, not hg minus hf. That overstates heat and fuel rate.
- Wrong flow basis: Steam flow per hour vs per day mixed with fuel per hour gives huge error.
- Efficiency as 0.88 vs 88: Enter 88 for 88%, not 0.88. Calculator handles percent.
- Forgetting blowdown: Fuel to make blowdown steam is extra. Add blowdown to steam flow for total feedwater heat.
- Gas volume vs mass: Nm3/h needs GCV in kJ/Nm3, not kJ/kg. Use correct pair for your system.
How to Reduce Fuel Consumption
- Raise feedwater temp: Economizer can add 15-30°C. Each 6°C saves about 1% fuel rate.
- Return condensate: Hot condensate at 80-90°C replaces cold makeup and cuts fuel and water treatment cost.
- Tune excess air: Keep O2 at 2-3% for gas. High excess air raises stack loss and fuel rate.
- Fix steam leaks and traps: Failed traps waste steam and raise fuel rate for same useful output.
- Control blowdown: Auto TDS control cuts blowdown from 8% to 2-3%, saving fuel and water.
- Clean heat transfer surfaces: Soot and scale raise stack temp and lower efficiency, pushing fuel rate up.
Frequently Asked Questions
How do you calculate boiler fuel consumption?
Fuel = Steam flow × (h_steam - h_feed) ÷ (GCV × efficiency). Use same units for heat and same basis for GCV and flow.
What is evaporation ratio?
Steam flow divided by fuel flow. It tells how many kg steam you get per kg fuel or per Nm3 gas. Higher is better.
How much fuel does a 1 TPH boiler use?
At 10 bar, 85°C feed, 88% efficiency and gas GCV 35,500 kJ/Nm3, 1 TPH needs about 77-78 Nm3/h gas. With coal GCV 21,000 kJ/kg it needs about 150 kg/h.
Why does feedwater temperature affect fuel rate?
Boiler heats water from feed temp to steam temp. Hotter feed means less heating needed, so less fuel per kg steam.
Can I compare gas and diesel fuel rate?
Yes, use same steam duty and efficiency, enter each fuel GCV. Calculator gives rate in kg/h or Nm3/h and cost if you enter price. Compare cost per hour.
Does blowdown increase fuel consumption?
Yes, blowdown water is heated to boiler temperature then dumped. It adds to heat load. Include blowdown in steam flow for total fuel estimate or add 2-3% extra.
Related Boiler Calculators
Fuel rate ties to efficiency and pump sizing. Check these next for your system:
Basis: Direct method heat balance per ASME PTC-4. Saturated properties interpolated from steam tables 1-100 bar. Superheat approximated as hg + 2.1 × (Tsuper - Tsat). Feedwater enthalpy as 4.186 kJ/kgK. For acceptance testing use certified tables and measured efficiency.