How do you calculate the cost of steam per tonne?

Fuel needed per tonne of steam is 1,000 × (h_g − h_f) ÷ (efficiency × GCV). Multiply by the fuel price. Add water, chemicals and power for a fuller figure.

How much does a steam leak cost?

Estimate the leak with Napier’s approximation — 0.61 × hole area in mm² × absolute pressure in bar gives kg/h — then multiply by operating hours and the cost of steam per kg.

Module 12 · Efficiency and Audits4 min read

The Cost of Steam: Per Tonne, Per Fuel, Per Leak

Every improvement on a steam system is worth exactly what the steam it saves would have cost. Knowing the cost of a tonne of steam turns a leak, a failed trap or a bare pipe into a number a manager can act on.

ByShikhar Singh·Steam Consultant & IT Consultant·Published 13 October 2026

You'll learn

Calculate fuel cost per tonne of steam
Compare fuels on the same duty
Know what else belongs in the full cost
Price a steam leak

Before this: Heat balance and boiler efficiency, GCV vs NCV

BeginnerThe idea in plain words, and where you meet it. No maths.

From fuel price to steam price

Fuel cost per tonne of steam

C = \frac{1000 (h_{g} - h_{f})}{η \times GCV} \times price

Symbols in the formula
Symbol	Meaning	Unit
$h_{g} - h_{f}$	Enthalpy rise, steam minus feedwater	kcal/kg
$η$	Boiler efficiency on GCV	fraction
$GCV$	Gross calorific value	kcal/kg
$price$	Fuel price	₹/kg

The fraction is the fuel needed per tonne of steam; multiply by its price. Raise the feedwater temperature or the efficiency and the fuel falls; raise the pressure and it rises a little.

IntermediateThe formula, its units, and a worked example on real plant numbers.

Comparing fuels on one duty

Fuel cost of steam for 5,000 kg/h at 10.54 kg/cm²(g), feedwater 80 °C
Fuel	Fuel per hour	Steam per unit fuel	₹ per tonne of steam
Rice husk	1,234 kg	4.1	1,110
Indian steam coal	891 kg	5.6	1,158
Biomass briquette	986 kg	5.1	1,478
Natural gas (PNG)	361 SCM	13.9	2,741
Furnace oil	335 kg	14.9	2,813

Prices, calorific values and efficiencies are indicative figures from the steam cost calculator’s fuel table, not quotations. Replace them with your own.

Fuel is most of the cost, but not all of it. A full figure adds treated make-up water and chemicals, electricity for fans and pumps, labor, maintenance, ash disposal and the boiler’s capital cost spread over its life. Fuel-only is still the right figure for pricing savings, because those other costs barely move when a leak is fixed.

ExpertThe fine print: where the simple model breaks, and what it costs.

Pricing a loss

Worked example

A 3 mm leak at 7 kg/cm²(g)

Given

A 3 mm hole in a 7 kg/cm²(g) line, 7,200 h/year, coal-fired steam at ₹1.16/kg.

Napier’s approximation for choked flow: 0.61 × hole area (mm²) × absolute pressure (bar) = 34.0 kg/h.
Per year: 34.0 × 7,200 = 244.6 t.

Answer: About ₹2,83,150 a year, from one hole the size of a pencil lead.

Key takeaways

Fuel cost per tonne of steam = fuel per tonne × price; fuel per tonne = enthalpy rise ÷ (efficiency × GCV).
Compare fuels on the same duty, with each fuel’s own efficiency.
Price savings at the marginal cost — mainly fuel, water and chemicals.
Small leaks cost lakhs a year; put a number on them.

The Cost of Steam: Per Tonne, Per Fuel, Per Leak

From fuel price to steam price

Comparing fuels on one duty

Pricing a loss

Key takeaways

Check your understanding

Frequently asked

Work it out

Related equipment

Training a boiler team?

Sources

About the author