We highly recommend using this pipe when installing a outdoor furnace for many reasons. Regular pex has a very high expansion ratio; 1.1 inch per 100 feet per 10° F. Which means 100 feet of line 110° F above the ambient temperature of the pipe can expand 6 to 7 inches laterally. The expanded line pushes against the pump and fittings attached at either end. Pex-al-pex lines have expansion properties similar to copper. There are no special considerations for expansion during the installation. When used with hot water the expansion is minimal. Lines maintain their shape and underground runs do not exert extra pressure on pumps or fittings. Pex-al-pex lines also have a full 1 inch inside diameter (ID) compared to 1 inch pex lines that have an ID slightly less than 7/8 inches. This difference in ID makes a big difference when transferring BTU with hot water. Pex Al Pex also has a layer of aluminum in between two layers of plastic which acts as a oxygen barrier. Sold by the foot.