If you have a preasure regulator on your water service or a check valve in your service it may be necessary to install a line preasure expansion tank. You can check by installing a preasure guage on your water line on the house side of the regulator/check valve, run your hot water until the water cuts in, shut off ALL faucets, and recheck preasure when the W/H shuts off. If the preasure goes above 80lb. you should add an expansion tank.