Looking for a split nut heater union? Split nut unions are used to attach the hot tub heater manifold to the spa plumbing. Split nuts are available as an option to repair broken pump unions instead of re-plumbing. Split nuts come in a variety of sizes, 1.5", 2" and 2.5" normal and split nut repair unions. Split nuts are easy to install, as they all split open and are fastened with 2 screws which are included.