Calculate boiler efficiency from steam output and fuel input using typical steam and fuel values, or from heat losses, or find fuel use at a given efficiency.

Direct method: useful steam energy divided by fuel energy supplied. Typical steam, feedwater and fuel values are preselected; choose Custom to enter your own.

Dry saturated steam enthalpy from steam tables. Choose Custom for superheated steam or a measured value.

Typical values; your fuel supplier’s analysis is more exact. The value used follows the heating-value basis below.

Higher is gross; lower is net. Use this same basis for losses and target efficiency.

Target efficiency and annual fuel cost
Blank omits the target comparison; no efficiency improvement is assumed.

Enter both hours and fuel price for annual cost (with a target efficiency in the efficiency mode).

A constant price for this simple operating-cost estimate.

Boiler Efficiency Formula

The following formula is used to calculate the direct efficiency of a boiler.

E = [Q × (H - h) / (q × GCV)] × 100
  • Where Q is the quantity (or flow rate) of steam generated (kg/hr)
  • H is the enthalpy of steam (kcal/kg or kJ/kg)
  • h is the enthalpy of feedwater (kcal/kg or kJ/kg)
  • GCV is the gross calorific value (higher heating value) of the fuel (kcal/kg or kJ/kg)
  • q is the quantity (or flow rate) of fuel consumed (kg/hr)

Boiler Efficiency Definition

Boiler efficiency is defined as the percentage of input energy that a boiler can convert into output energy in the form of steam.

How to calculate boiler efficiency?

First, determine the quantity of steam the boiler generated. For this example, the quantity of steam generated by the boiler is 10 kg/hr.

Next, determine the enthalpy of the steam that is generated. For this example, we will use the enthalpy of saturated steam at standard atmospheric pressure ≈ 2676 kJ/kg.

Next, determine the enthalpy of the water input into the boiler. For this problem, the input water is at 60 degrees Celsius. At this temperature, water has an enthalpy of about 251.18 kJ/kg.

The next step is to determine the gross calorific value of the fuel. For this illustrative natural-gas example, assume a gross calorific value of 12,500 kcal/kg (≈ 52,300 kJ/kg); actual fuel properties vary.

Next, determine the quantity of fuel. To match the steam production rate given above, we will use a fuel consumption of 0.6 kg/hr of natural gas.

Finally, calculate the efficiency using the formula above:

E = [ Q * (H-h) / (q*GCV) ] * 100

= [ 10 * (2676-251.18) / (0.6*52,300) ] * 100

= 77.27%.