Combustion thermal energy calculator

Description

q - Volume flow rate

Fuel flow rate in terms of units of volume per unit of time

ṁ - Mass flow rate

Fuel flow rate in terms of units of mass per unit of time

P - Power - heat power

Energy needed for combustion in unit of time

P1 - Actual power

Useful heat energy - power after reduction due to energy losses in energy conversion from combustion heat to, for example, hot water heat energy

LHV_V - Heat value

Heat energy created during combustion in units of volume

LHV_G - Heat value

Heat energy created during combustion in units of mass

ρ - Density of fuel

This value is only required if you want to calculate flow rate or heat power in different units (as per unit of mass or volume).

η - Efficiency

Energy losses coefficient ratio between actual heat power and combustion heat power that represents efficiency of energy conversion.

Efficiency coefficient is used to represent losses in energy conversion from combustion energy to energy available for end use like hot water heat energy from boiler. If you have specified hot water heat energy demand P₁ and if you know boiler efficiency - η, calculator gives you required actual heat power from combustion like P₁/ η. You can select not to use this feature by selecting η in Omit section.

Calculation setup

Select value to calculate. You should input values for not selected one.

P

heat power calculation

ṁ

fuel flow rate calculation

LHV_V/LHV_G

fuel heat value calculation

Select value to input. Not selected one will be calculated.

P

heat power

P₁

actual heat power

Select value to input. Not selected one will be calculated.

q

volume flow rate

ṁ

mass flow rate

Select value to input. Not selected one will be calculated.

LHV_V

lower heat value in terms of volume

LHV_G

lower heat value in terms of mass

Use η in calculation

for calculation of actual energy after energy losses in combustion process

Use ρ in calculation

for conversion between mass and volume

When Should You Use This Combustion Energy Calculator?

This combustion energy calculator is ideal for calculating the thermal power (heat energy per unit of time) released during the combustion of liquid or gaseous fuels. It also supports reverse calculations—you can determine the required fuel flow rate based on a known heat power demand. This flexibility makes the tool useful for engineers, HVAC designers, and anyone planning fuel consumption or thermal energy requirements for heating or industrial applications.

Available calculation scenarios

1. Fuel Flow Rate Calculation for a Given Heat Power

If you know the desired heat output (thermal power), this mode calculates how much fuel you need to burn to achieve that output. Useful for sizing boiler systems, heaters, and industrial furnaces.

2. Heat Power Calculation from a Known Fuel Flow Rate

If you already know the fuel flow rate (mass or volume), this option calculates how much thermal energy the combustion will produce, helping you evaluate system performance or energy efficiency.

3. Fuel Heat Value Calculation from Flow Rate and Heat Power

If both the fuel flow rate and the resulting thermal power are known, the calculator can estimate the fuel's heat value (quality of fuel), which is essential for comparing different fuels or verifying fuel specifications.

Additional Inputs Needed for Accurate Calculation

You can enter the fuel flow as either mass flow rate (e.g., kg/h) or volume flow rate (e.g., m³/h). If you provide the fuel density, the calculator automatically derives the missing flow parameter for you.

You also have the option to include or omit energy efficiency in your calculations.

By specifying an efficiency coefficient (η), you account for energy losses during the conversion process—for example, losses between combustion energy and usable energy output (such as hot water heating via a boiler).

If you know your thermal energy demand and the boiler efficiency 𝜂, the calculator will determine the required combustion energy as:

If you prefer to ignore efficiency losses, simply select the "Omit Efficiency" option