During the coldest days of winter, fuel oil in outdoor tanks can suddenly stop flowing. HOT 4 in 1 is a highly effective product to keep your heating system running. Stay warm. Stock up now and stay ahead of the bad weather. Its specially formulated solution: disperses water that causes fuel line and fuel filter icing reduces normal accumulation of water in the tank and turns it into a combustible solution eliminates sludge so the fuel oil reaching the nozzles is clean provides for more complete combustion and less smoke saves money through better fuel economy