A hemodiafiltration system with a disposable pumping unit is disclosed. An example system includes a medical fluid pump actuator, a medical fluid heater, a blood filter and a disposable unit. The example disposable unit includes a medical fluid cassette portion including a medical fluid cassette housing configured to be operatively connected to the medical fluid pump actuator to pump medical fluid through the medical fluid cassette portion when the medical fluid cassette portion is in fluid communication with a medical fluid source. The example medical fluid cassette portion is also configured to be placed in fluid communication with the blood filter and with an extracorporeal circuit communicating with the blood filter, the fluid communication enabling hemodiafiltration to be performed. The example disposable unit also includes a heater bag configured to be placed in operable communication with the medical fluid heater and in fluid communication with the medical fluid cassette portion.