In the present study, the performance of a vertical inline drain water heat recovery heat exchanger is investigated. The system recovers the heat with the aid of a heat pump. To produce quality measurement data for the analysis special attention have been given to the calibration of sensors and the analysis of the propagation of uncertainty. The results from the analysis of the heat exchanger reveal that the contact resistance between the two copper pipes and the heat resistances on the inside of the drain water pipe are the dominating resistances to the heat transfer. Investigation of the heat recovery ratio shows that the heat exchanger has the capability to recover more than 25% of the available heat in the drain water at the flow rates investigated.