Coverting Lower-Heating Value (LHV) to Higher Heating Value

[Rick]

What is the multiplier to convert a Lower Heating Value (LHV) to a Higher Heating Value (HHV)

[Guest]

There is not a constant ratio. It depends on the carbon-hydrogen ratio of the fuel. You need to know the amount of water vapor resulting from combustion, and its heat of vaporization. That heat is the difference between upper and lower heating values.

Unless you can actually usefully recover the heat of vaporization (you condense the water formed in combustion) in your application, the lower heating value is the relevant one. For any given fuel, you can just redefine efficiency instead, but when comparing alternative fuels, compare on LHV.