<p>In machine tools, increases in rotational speed and feed rate result in increased frictional heat, leading to thermal deformation and decreased machining accuracy. When analyzing thermal deformation, it is critical to accurately estimate the heat quantities at heat sources. To reduce machining errors induced by the thermal deformation of machine tools, we recently proposed a method to estimate the steady-state heat flux acting upon a machine tool body. In this method, quasi-steady-state increases in machine tool body temperature are used to estimate the heat flux at the heat source with sufficient accuracy for practical use. In this paper, an objective function Δ _j, for which the ideal value is 0 K², was obtained from the residual sum of squares between measured quasi-steady-state temperatures rises and those obtained by finite element analysis at all evaluation points, and the effects of the layout and number of temperature sensors on the accuracy of estimated heat quantities at steady-state heat sources were evaluated. The results suggest that the layout and number of temperature sensors should be selected to include temperature evaluation points where factorial effects are large, which are obtained using S/N ratios defined as smaller-is-better response in quality engineering. Where Δ_j became smaller than 100 K², the heat quantity at the steady-state heat source could be estimated from the intercept of the approximate linear regression equation given by least squares method between the optimal solution and Δ _j. Locating the temperature evaluation points both close to and far from the heat source is useful to decrease the number of points. Setting the initial steady-state heat flux at the heat source in consideration of the approximate steady-state heat quantity is an effective method to decrease the search time for optimal estimated heat quantity.</p>