To overcome the problems of staircasing errors at boundaries when using FDTD techniques in the modeling of thermal effects, a new conformal technique is proposed that can be integrated easily into existing implementations. It scales fluxes at interfaces with factors derived from the local surface normal. The new scheme is validated using an analytical solution, and an error analysis is performed to understand its behavior. Further, it behaves considerably better than the standard scheme and, in contrast to the standard scheme, it is possible with it to obtain more accurate solutions by increasing the grid resolution.