The effect of insulators in a Czochralski furnace on the power consumption and the oxygen content in the melts as well as in the Si ingots was investigated with no radiation shield by using a commercial software, Femag-Cz. Location and thickness of the insulator were changed. The calculated results with no radiation shield were compared to those with radiation shield. The top insulator showed better results than the top-side and bottom insulators for the power consumption and Si melt temperature in the calculations of separately installed insulators. The oxygen content in the melt decreased with increasing the thickness of insulators for the top and top-side insulators. Installation of insulators at the three locations at the same time, the power consumption and the oxygen content in the melt and the Si ingot were improved compared to those of separately installed insulators. (Received March 10, 2014)