Abstract The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance for two effectiveness heat exchanger values have been presented for absorption heat transformers operating on an aqueous ternary hydroxide working fluid consisting of sodium, potassium and caesium hydroxides in the proportions 40:36:24 (NaOH:KOH:CsOH). The interactions of operating temperatures have been illustrated graphically.