My dad and I installed a state powervent water heater this weekend. The pressure relief valve feels warm to the touch. I think my system might be closed. There is a brass bell shaped piece after the water meter. If I need an expansion tank how do I install and how long do I have before I damage my brand new unit?

First you have to understand a expansion tanks function. When new codes forced us to install check valves and backflow preventers, such as you just described , on water service lines that it could no longer expand back along the water service line and would build up pressure in the system this would kick off the T & P ,(Temperature and Pressure Relief) valve and the valve would discharge hot water out the relief line. To prevent this we installed a Expansion,(Air) tank,(see image) on the heaters cold water supply line for some place the water to expand to..

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how long do I have before I damage my brand new unit?

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The most that can happen to your water heater is that the hot water expansion will cause the PRV(pressure Relief Valve) to open up and release water. Your heater won'tbe harmed. As you can see by the image cut a tee into the cold water supply and connect the expansion tank to the tee.
Good luck, Tom

Great advice from Tom. However, your tp vavle will naturally feel warm to the touch, as its in direct contact with the hot water in the heater. This is normal. As long as the tp valve is not leaking or blowing off, I'm not sure I would worry about this too much. If you are really concerned about it, then follow Speedballs advice, but know that the relief valve will still feel warm to the touch, just the nature of the beast. Good luck and please let us know what you decide, and how things work out.

MGD's right on the money. Your PRV valve will always stay warm but I focused on the backflow preventer that you described. That makes your system a closed one. Regards, Tom

Hello all the T&P and PRV are two different valves, I am sure that Tom and lee are talking about the T&P valve which is installed on the water heater and it in normally hot due to direct contact with the hot water, the PRV is always cold as the cold water flow through it, I would not worry about the T&P valve that is hot, see tha images below,Thanks.

Regards,
John

Thanks for the help. I think I'll just leave well enough alone. The instructions had me scared because it says "thermal expansion can cause premature tank failure" and "the tpv is not intended for the constant relief of thrmal expansion" but the old unit was still good from at least 1994 w/o an expansion tank so I'm calling it good and moving on to the next project. Thanks again.

You are welcome

John caught us. He'scorrect we meant the T&P valve. However if you ,indeed, have a closes system and fail to install a expansion tank expect the T&P valve to open up and release water every time the water heats up and expands just like in the picture above. Good luck anyhow, Tom