We have heard a lot of mixed opinions on thermal expansion tanks. Our last water heater never had one but now the plumbers that came out are telling us we have to have one.
We usually don’t recommend expansion tanks unless it’s required by city code. You can check your city by clicking on the city page on the right sidebar. The thing that you need to consider is that expansion tanks will fail over time. They also require maintenance on a yearly basis. When an expansion tank fails, it fills with water. Eventually the weight of the water can cause major flooding. We can come out to test to see if your house has thermal expansion to see if a tank is needed.