Gas Heating Value: HHV vs LHV Explained

What is Heating Value?

The Heating Value (often called Calorific Value or Heat of Combustion) of a fuel gas is the exact amount of heat energy released when a specific quantity (volume or mass) of the gas is completely oxidized (combusted) with oxygen.

In the natural gas industry, this is arguably the most important physical property of the fluid. Natural gas is not sold by volume or mass; it is bought and sold entirely based on its energy content. Therefore, accurately knowing the heating value dictates the monetary value of the gas stream at the custody transfer meter.

Heating value is typically expressed in volumetric energy units, such as $MJ/Sm^3$ (Megajoules per Standard Cubic Meter) or $BTU/scf$ (British Thermal Units per Standard Cubic Foot).

The Critical Difference: HHV vs. LHV

When hydrocarbons burn, the carbon atoms form Carbon Dioxide ($CO_2$), and the hydrogen atoms form Water ($H_2O$). The physical state of this byproduct water dictates which heating value you are measuring.

Higher Heating Value (HHV)

Also known as the Gross Calorific Value (GCV). The HHV assumes that all the water produced during combustion is allowed to cool down and condense back into a liquid.

When water vapor condenses into liquid water, it releases its latent heat of vaporization back into the system. Therefore, the HHV captures the absolute maximum theoretical energy available from the fuel.

Industry Standard: In North America and the UK, natural gas billing and pipeline tariffs are almost exclusively based on HHV. A typical pipeline specification requires an HHV between 950 and 1050 BTU/scf.

Lower Heating Value (LHV)

Also known as the Net Calorific Value (NCV). The LHV assumes that the water produced during combustion remains as a vapor (steam) and exits the exhaust stack of the burner or turbine.

Because the water does not condense, its latent heat of vaporization is lost to the atmosphere and cannot be utilized by the process.

Industry Standard: In Europe, and globally for almost all gas turbine and internal combustion engine performance calculations, LHV is the standard metric. For natural gas, the LHV is roughly 10% lower than the HHV.

Calculating Mixture Heating Value

Like apparent molecular weight, the overall heating value of a natural gas mixture is simply the statistically weighted average of the pure heating values of its individual components.

The calculation uses the mole fraction ($y_i$) (or strictly speaking, the ideal volume fraction):

Where $y_i$ is the mole fraction, and $HHV_i$ is the standard molar or volumetric heating value of pure component $i$ at standard conditions.

The Detrimental Impact of Inert Gases

Not all gases burn. Nitrogen ($N_2$) and Carbon Dioxide ($CO_2$) are fully oxidized or inert gases. Their heating value is strictly zero ($0 \ BTU/scf$).

If a natural gas well produces a mixture containing 15% $CO_2$, the overall heating value of the mixture will drop drastically. This gas will likely fail to meet the minimum pipeline tariff requirement (e.g., 950 BTU/scf). To sell this gas, the operator must build an expensive Amine Sweetening plant to strip out the "dead weight" $CO_2$ and raise the heating value of the remaining residue gas.

Worked Example

Consider a simple gas mixture:

• 95.0% Methane ($HHV \approx 1010 \ BTU/scf$)
• 3.0% Ethane ($HHV \approx 1770 \ BTU/scf$)
• 2.0% Carbon Dioxide ($HHV = 0 \ BTU/scf$)

Calculation:

This gas comfortably meets standard pipeline specifications.

Try the Calculator

Don't guess your heating values. The Gas Intelligence Engine on this page uses the exact ISO 6976 standard pure-component enthalpies of combustion to instantly calculate both the HHV and LHV for any custom natural gas mixture!