This study deals with a type of thermally driven heat pumps that consists of a reverse Rankine heat pump cycle, the compressor of which is driven by the turbine of a supercritical Organic Rankine Cycle (ORC). The application is residential heating (domestic hot water and floor heating) of small buildings requiring a cumulated thermal power of approximately 40 kW. An approach that enables the comparison of performance that can be expected with different working fluids is presented. It appears that R134a, R1234yf, R227ea and R236fa are among the best candidates. An off-design simulation tool of such thermally driven heat pumps has been implemented that includes both turbine and compressor off-design models. This thermally driven heat pump model has been used to predict the performance of an existing experimental prototype about to be tested.