How necessary is it to install an expansion tank along with a new hot water heater? I understand that this may be a code requirement, but I just want to know if it is really necessary. I have never had one in my current home and am finally replacing the hot water tank, so I thought this would be a good time to check into it.

Thanks

I am not aware of this as a code requirement as much as I know they are needed only when a house has a "closed" system, which can mean backflow preventers or check valves on the water main and that usually makes the T&P valve leak periodically.

If your old water heater had an expansion tank, it should still be good and you should be all set. If this is actually a NEW code requirement in your area it is, most likely, a result of something the water department has done, such as install new water meters with check valves (or they intend too down the road). A quick call over to your water department should tell you if needed or not!

Mark

just want to know if it is really necessary
Only really necessary if your T&P valve periodically releases water.

Not addressing any code requirements.

If there is none currently in the home it is unlikely that you will need one now. If you experience issues in the future come back here and we can talk further