I install expansion tanks on almost every water heater I put in. Even if there is no PRV I still recommend installing the expansion tank.
Sometimes, I feel like the customer is not buying into the idea of the expansion tank and thinks I'm just trying to sell them on things they don't need.
"My last water heater lasted for 20+ years and did just fine without an expansion tank" is the most difficult type of statement to rebuttal.
I usually tell them that water heaters are not built like they were in the past and that also the city water supply can be tougher on water heaters than in the past. I also let them know that it's code for many applications.
Looking to get some feedback from other professional plumbing contractors and their thoughts on Thermal Expansion Tanks.