Disclosed are hemodialysis and similar dialysis systems including fluid flow circuits. Hemodialysis systems may include a blood flow path, and a dialysate flow path including balancing, mixing, and/or directing circuits. Preparation of dialysate may be decoupled from patient dialysis. Circuits may be defined within one or more cassettes. The fluid circuit and/or the various fluid flow paths may be isolated from electrical components. Fluid circuits and electrical components may be contained in a housing comprising a first section separated from a second section by a thermally insulating barrier. The first section may house a heater and heat-sterilizable components including liquid flowpaths, pumps or valves, while the second section houses electronic components for controlling the hemodialysis system. The insulating barrier may be configured to inhibit the second section from being exposed to sterilizing temperatures produced in the first section.