Extinguishing smoldering fires is a severe challenge for fire brigades, and has proven to be difficult even on the lab scale. In this study, the influence of a closed water cooling loop located within the fuel bed was investigated experimentally. Increasing the cooling led to a system less prone to intense combustion at an early stage, and eventually to complete extinguishment of self-sustained smoldering fires. Extinguishment was obtained in half of the cases with maximum cooling. Extinguishment occurred soon after smoldering had been established, giving a significant reduction in fuel consumption compared to the self-sustained smoldering fires that continued to complete burn-out.