This paper dealt with thermal storage efficiency due to difference ($T_{infty}-Ti$) between the mean temperature of water in the storage tank [$0.5m{ imes}0.5m{ imes}1.0m$] and the temperature of water flowing into the tank, flow rate of water flowing into the tank and shape of porous manifold which water flow into the tank through. As results of experiments; (1) When the flow rate was constant and the diameter of porous section decreased by 8mm, 6mm, and 4mm, the thermal storage efficiency increased. (2) When the diameter of porous section was constant and the difference ($T_{infty}-Ti$) between the mean temperature of water in the storage tank and the temperature of water flowing into the tank increased by -30, -20, -10, 5, 10, 15 ($^{circ}C$), the thermal storage efficiency increased. (3) When the($T_{infty}-Ti$) was constant and the flow rate decreased by 0.8, 0.4, 0.25(LPM), the thermal storage efficiency increased. (4) When the shape of porous section was rigid, the thermal storage efficiency was the most effective, and with establishing flexible porous section or mesh, the effective thermal storage efficiency was obtained.