PURPOSE: To easily forecast the time when Gitter bricks are to be repaired by re-laying or other method by subtracting a resistance change due to difference is operational conditions from gas permeation resistance calculated from a pressure drop caused by the bricks to obtain a change of the gas permeation resistance with the lapse of time and by estimating the deterioration of the bricks according to the change.

CONSTITUTION: Pressures at upper and lower positions of the laid Gitter bricks of a hot stove are measured to obtain a pressure drop ΔP and gas permeation resistance K is calculated from the pressure drop ΔP. A resistance change ΔKop due to difference in the operational conditions of the hot stove is calculated and subtracted from the gas permeation resistance K to obtain a change Ktime of the resistance K with the lapse of time due to the deterioration of the bricks. The deterioration of the bricks is estimated according to the change Ktime.