Does an Electric hot water tank on well water need a vacuum breaker valve?

A vacuum breaker is a device built into or added on to hose bibs to prevent contaminated water from being sucked into a municipal system should the system loose pressure.

A well system could have such a device installed but usually the well piping has a foot valve or a check valve built into the system such that vacuum breakers on hose bibs are not necessary. If one were installed on a well system it would be on the well tank not the water heater.

All water heaters have a T&P (temperature and pressure) valve installed, if by some chance that is what you mean.

You are wondering if you need to install a vacuum RELIEF VALVE... see image.

The straight answer is that some states require them and some don't (my state does require these), so it is not something that is related to well systems exclusively... backflow can occur with well systems or, for example, on city/town supplied water when a neighbor throws his/her water hose into a pool.

The only way to know if a vacuum relief valve is needed in your area would be to look up the local codes OR call a local plumbing inspector and ask him.

Good luck!

Mark