Some municipalities require them, but they are needed in a closed system,(if you have a backflow/check valve device on your water supply), some municipalities have backflow/check valves built into the water meter. There is a ball valve that has a expansion relief built into them, just do some googling for different thermal expansion products I've seen a 3 year old house piped in cpvc that blew the water piping due to thermal expansion, not just leak but blew the piping to shit, the cpvc was stretched so thin you could see through it.






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