Why does my water heater have an expansion tank (top of tank) just past the shutoff valve? I cool & heat my house with a heatpump. Many thanks. I would like my son to install a tank on his newly installed water heater. I’m sure it must be (in my house) there as a saftey reason, but am not sure.
The expansion tank absorbs the expansion of the water as it heats up. If this expansion is not absorbed or releived, the water pressure will rise until a relief valve opens and relieves the pressure. Some locations do not need expansion tanks because the utility company’s water main will be able to absorb the expansion. It depends on the water supply pressure and if their is anything that will prevent the water from backflowing to relieve pressure.