I just had the water heater replaced. The plumber suggested adding an expansion tank. I asked him why and he said the water expands when heated.

If the tank is directly connected to the municipal supply at 60 psi, how can there be a pressure buildup in the tank? It seems to me the water will expand back into the supply and 60 psi will be maintained.

What am I not getting?

 

Ripped off

 

The plumber was correct, that is why the expansion tanks are used.

Many municipal systems are installing back-flow preventers (check valves) in the supply laterals that serve each customer's premises. These valves are specifically installed to PREVENT water from flowing backwards to prevent potential contamination of the municipal supply. If your water company has done this, you NEED an expansion tank in your home. If you do not install one, the water system pressure will spike when cold water comes in, gets heated, and expands. If you're lucky, the T&P valve will "leak" and relieve the pressure. Many homeowners will see this and replace the T&P valve, sometimes several times, before they ask the right question of the right person.

In many jurisdictions around here where the check valves are in use, the addition of an expansion tank is mandatory (local code) with a water heater replacement or new installation.

If you're on a private well, this doesn't apply. Most private wells already have a pressure tank and no backflow preventer.

 

Hot water doesn't need heating?

Yeah I still don't understand. I need to what because they did something somewhere else?

 

Second that, I put one on mine to cut back on "hammer effect" worked fairly well.

 

I replaced mine after it started leaking last summer. It helps with water hammer, too. It may also be local code deal too.

 

Thank you, project. Now I understand the physics. I am going to call the water company to see if the backflow valve is on my meter. If not, I will "T" in a tank. They are cheap.

 

Around here, they doubled in price when the code started requiring them.

 

To close this issue out, I just talked to the building department. I am in Silicon Valley and the code is strict.
If pressure is over 80 psi, an expansion tank is required here. Mine is at a rock steady 60 psi so I will pass.
Thanks, project.

 

They are super easy to install and swap out. So is a check valve.

 

Not when it's installed at or in the service meter which is where the water utilities put them.