Energetic ionic liquids have obtained substantial attention the last decades as less toxic, or green, monopropellants to replace the carcinogenic and toxic hydrazine. Among the most promising hydrazine substitutes are propellants based on ammonium dinitramide, ADN, dissolved in a fuel/water mixture. These types of propellants are single phase mixtures, and thus their heats of formation are influenced by the heats of solution and heats of mixing of the respective components used. These enthalpy contributions have been measured for three different ADN-based propellants (LMP-103S, FLP-106 and FLP-107) and their specific impulses have been calculated. The results show that ADN heat of solution must be considered in order to accurately calculate the specific impulse.