A high resolution thermoelectric vacuum calorimeter for tritium measurements is described in detail. The results and experience gained during the measurement of different tritium samples with the vacuum calorimeter as well as comparisons with measurements from other calorimeters are presented. Special specimens have been cut to fit within the measuring volume of 0.5 litre. With the low detection limit of the vacuum calorimeter, tritium in tiles can now be measured by calorimetry for the first time.