Will my oil lines freeze if my tank is installed outside?

No, but lines could gel if temperatures are extremely low for long durations. If you have a long existing supply line then the fuel may thicken in the line and gel the oil.  We recommend covering the lines with insulation in this case. CommTank installs all our tanks with a supply and return line. This ensures the fuel is always moving.  We install fuel filters inside the basement and close to the furnace to minimize gelling because an uninsulated fuel filter is more likely to have gelled fuel when installed outside. For homes without a basement, extra insulation is required.  (This is common with mobile homes or ranch style homes without a garage.)