Heat Input Calculator

The Denominator Behind Every Efficiency Calculation

Heat input is the total fuel energy fed into a boiler or furnace, the baseline figure that efficiency calculations divide useful heat output by. Getting this number right is the foundation for any accurate efficiency check.

The Formula

Heat Input = (Fuel Flow(kg/hr) × Heating Value(MJ/kg)) / 3.6

Worked Example

A boiler burning 25 kg/hr of fuel oil at 41 MJ/kg:

Heat Input = (25 × 41) / 3.6 = 284.7 kW

How to Use This Calculator

Enter the Fuel Flow Rate in kg/hr.
Enter the fuel's Heating Value in MJ/kg.
Select Calculate to get heat input in kW.

Related Calculations

Use this to find boiler efficiency in the Boiler Efficiency Calculator, or check heat loss in the Heat Loss Calculator.