This paper relates generally to windows and doors for traditional Korean houses (Hanok). Especially, we focus on the minimizing the thermal losses on the windows and doors where the highest heat loss come to pass. The door includes a structure of a lattice door framed with vertical lattice frames and horizontal lattice frames which are arranged in a regular periodic pattern. The suggested method uses the convection flows to reduce thermal losses by structural formation of window and door's lattice without damaging the original aesthetic characteristic of windows and doors in Korean traditional wooden house. Based on computational analysis, we propose specific structures like as lattice aspect ratio of windows. A lattice aspect ratio of the lattice door ranges from 0.07 to 0.1 so that the vortex, air layer, induced by natural convection flow prevents thermal loss of a room from going out toward the outside air. Therefore, energy consumption can be reduced.