How this calculator works
Higher heating value includes the heat recovered when combustion water condenses; lower heating value leaves that water as vapour. Enter positive heating-value magnitudes at the same reference conditions, then subtract the vaporization contribution. Pure-fuel names provide a stoichiometric water reference but do not replace your measured heating values or amounts. Kerosene, diesel, wax and natural gas vary in composition; use the mass basis and measured water production. The 44.01 kJ/mol default is near 25 C, not the boiling-point latent heat.
Formula
LHV = HHV - (nwater/nfuel) Hvap on a kJ/mol fuel basis. On a mass basis, subtract nwater Hvap/(1000 mfuel) in MJ/kg. Mwater = 18.015 g/mol from IUPAC weights.
Worked example
With HHV = 1000 kJ/mol fuel, 2 mol water per mol fuel and Hvap = 40 kJ/mol water, LHV = 920 kJ/mol. A lower value of 800 with one mol water and Hvap 40 implies HHV = 840 kJ/mol.
Advertisement
Frequently asked questions
Why are heating values positive?
They describe released heat magnitudes. Thermodynamic combustion enthalpy normally carries a negative sign.
Do fuel names supply standard heating values?
No. They show ideal complete-combustion water ratios; enter the appropriate measured heating value and water amount.
Which water latent heat should I enter?
Use the value at your heating-value reference temperature and keep higher and lower values on the same basis.