A physically based heat pump model was connected to an optimization program to form a computer code for use in the design of high-efficiency heat pumps. The method used allows for the simultaneous optimization of selected design variables, taking proper account of their interactions, while constraining other parameters to chosen limits or fixed values.For optimization of the steady-state heating efficiency of conventional heat pumps, ten variables were optimized while heating capacity was fixed; the results may, however, be scaled to other capacities. Calculations were made for a range of component efficiencies and heat exchanger sizes. The results predict substantial improvement in heating performance due to both optimal system configurations and the use of improved components.Sensitivity analyses show that there is considerable latitude for deviating from the optimum design to make use of available component sizes and for accommodating the compromises needed for good cooling performance.