I am replacing the tank on my 20 yr. old Cornell batch solar heater. Original tank is galvanized. I can get a galvanized tank to fit with a rating of 150psi. Is this sufficient or do I need greater psi? I used a std. hot water relief valve on it (150psi/210 degrees). Would I be better going for a stainless tank even though cost is much greater? Thanks for any help. Bill