This week I saw three times that my hot electric water heater was releasing water from the T&P valve for quite a long time. I checked with county and they said the water pressure is 50-70 psi. I checked with the water heater company tech person and he said I need expansion tank. How do I decide what pressure I need in my expansion tank? Releasing water once in a while from the T&P valve is the problem because of no expansion tank. Can some one explain. Thanks