A dialysis fluid flow control system includes a pumping cassette interface including a pump area operable with a pump chamber of a disposable cassette; the cassette interface further including a volumetric reference chamber used in a volumetric control of a dialysis fluid pumped pneumatically into and out of the pump chamber of the disposable cassette; a heater connected operably to the cassette interface; and a controller connected operably to the heater so as to cause the heater to heat at least a portion of the cassette interface to a desired temperature.