Experimental values for the viscosity of the radioactive hydrogen isotope tritium (T2) are currently unavailable in literature. The value of this material property over a wide temperature range is of interest for applications in the field of fusion, neutrino physics, as well as to test ab initio calculations. To measure the viscosity of tritium, a measurement setup has been built utilizing a spinning rotor gauge inside a Dewar. Temperature control is of high importance to produce accurate and precise values. To ensure high quality measurement results, prior to the tritium measurements, thermal simulations are done on measurements with protium and deuterium inside the sample gas volume of the spinning rotor gauge. •SRG viscosity measurements.•Thermal simulation to improve accuracy of the measurements.•Investigations for final measurements of the tritium viscosity in the zero density limit.