The presence of oil in domestic heat pumps is an obstacle toward higher efﬁciency, particularly for enhanced surface evaporators and for advanced concepts based on two- stage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the speciﬁcations, the choice for an appropriate refrigerant ﬂuid and the design of a proof of concept proto-type with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and ﬁrst experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efﬁciencies above 78%. The refrigerant chosen for this ﬁrst experimental approach is HFC 134a.