A Williamson furnace oil tank holds the oil that powers Williamson brand furnaces. Williamson is known for manufacturing high-efficiency furnaces that provide annual fuel utilization efficiency ratings in excess of 80 percent.
As of March 2015, oil furnace tanks feature dual layers of protection against leakage. Above-ground tanks feature an inside lining of fiberglass and plastic, as well as an outside wall made of steel designed to resist corrosion. Oil tanks are available in horizontal and vertical alignment, depending on the user's space requirements, and some companies offer custom-built tanks to fit in areas that have unique dimensions and shapes.