An expansion tank - for water heater - California region.

Hello,


Regarding houses in the California area.
Has anyone used or installed an expansion tank with a water heater installation.
What is the size of this, and is this a requirement. I have not seen any neighbors near
me perform this installation.


Thanks

Most water heaters in the 50 gallon range use the 2.2 gallon expansion tank, if the plumbing system is considered closed.

A closed system can occur with a check valve on the incoming water supply. Some water districts have those on their meters.
Without a check valve, the system may be "open". If that is the case, the expansion tank isn't required.

We require them regardless of the system.

Some places REQUIRE installation of an expansion tank for any WH. It is generally required everywhere if you have what is referred to as a closed supply system: i.e., one with either a check valve or a PRV to keep water pressure in the safe range. The sizing depends on your water temperature (both inlet and outlet), and the size of the tank of water you are heating. If you go to www.watts.com, you can find a calculator that will tell you the size you need for your application.

When water is heated, it expands. In a open system, you're actually pushing water back to the supply and paying for it twice (don't think your meter will actually record backwards!). And, if for some reason, your local water became contaminated, you'd be pushing water back into the system for the rest of the people near you. So, many water companies install a check valve to prevent any water pushing back into their system. They may not tell you when they do it. This can create a closed system that you didn't know was there and then things start leaking. The pipes don't stretch much, and water doesn't compress much, so when it gets bigger in volume, the pressure rises and something has to give. This is often the T&P safety valve on the WH, but could be anywhere there's a weak seal or hose.

If your local code does not require one, and you don't have a closed system, then you don't need one, but it doesn't hurt to have one. They don't last forever, but are simple to replace (often an easy DIY job) when they do fail.

A thermal expansion tank is needed anywhere when certain conditions exist. First, you need to understand a couple of basic principals of physics. Heated water expands and water does not compress. When a water heater heats water, the water expands and has to go somewhere. If the water supply pressure does not come through a pressure regulator valve (PRV) to reduce overly high pressure, the expansion simply is absorbed by the city water main. This is called an "open system". However, many times the incoming pressure is too high and a PRV is installed to lower the pressure. Within the PRV, there is a check valve that prevents the expanded water from passing through and back into the water main. This is called a "closed system". Since water will not compress, what happens to the expansion? It builds up pressure in the water heater until the safety limits of the temperature/pressure valve on the water heater is reached. At that point the T/P valve opens and relieves the pressure. If working properly, a fairly small amount of water is released, the pressure is reduced, and the valve closes. A bit of a puddle of water, but not a flood. Sometimes the T/P will stick and not close and you do get a flood. Now enter the thermal expansion tank. This is placed in the water supply between the water heater and the PRV. It's internal air pressure is adjusted to match the PRV's pressure setting, and when the water expands it is absorbed by the expansion tank. When the heating stops, the pressure lowers and the expansion tank releases the collected water back into the system. Some newer water meters being installed by cities today have a check valve built into them so even without a PRV, you would have a closed system. In addition, some PRVs have a bypass which allows the pressure build up to pass. First thing to do is to get a decent pressure gauge and determine what your incoming water pressure is. The best kind has two needles. One to record the highest pressure of the day or night, and the other the current pressure. Sometimes pressure is is considerably higher at night than in the daytime. If you do need a PRV and expansion tank, you will need a gauge to set the PRV and expansion tank pressure. It's kind of nice to know what your pressure is anyway.

Thermal expansion tank - California region

Thanks for all the responses. I have seen over a dozen water heater intalled.
However, I have not seen anyone with a thermal expansion tank.

I have even seen professional install by the big named store (H***) depot.
and I have not seen an expansion tank.


This is California region only.

Many of the big box stores do not pull plumbing permits, so what you see may or may not be what's required by local codes. Where I live, a WH installation requires BOTH a tempering valve AND an expansion tank. Lots of them out there with neither, but they didn't get it installed with a permit or home inspection.

The bottom line, if your local codes require an expansion tank, you should put one in. If you have a closed system (check valve or PRV), you need one. Otherwise, you can safely avoid installing one.

I have seen over a dozen water heater installed.
However, I have not seen anyone with a thermal expansion tank.

Click to expand...

And yet the plumbing code "requires" them in some instances.
We install expansion tanks on many of our installations.

Frankly, I prefer the expansion tanks installed even if they weren't required by code.

quote; In a open system, you're actually pushing water back to the supply and paying for it twice (don't think your meter will actually record backwards!). And, if for some reason, your local water became contaminated, you'd be pushing water back into the system for the rest of the people near you.

A mechanical meter will record backwards, but you are using a bit of hyperbole there. The amount of water "pushing backwards" is so small that the only water sent into the main would be that which is already in the pipe ahead of the water meter, not the water in the house.

Around here...the box stores do pull permit. The city does not mandate an expansion tank. All manufacturers recommend them, of course.

Bottom line is , if you have symptoms...dripping tp, etc, then you NEED it whether the city mandated it or not.

HJ makes an excellent point about the expanded water being pushed back or absorbed by the city water main. That is why many newer meters have a check valve built into them. It's not to save you from being charged twice for the water, it's a remote possibility that the water could be contaminated and infect the water supply. Now I don't want to make this sound like there is a big danger from this, it's likely some government agency with a need to prove their concern about public safety put this in the regulations and sold the idea to the code folks. But, regardless of the reasoning, the check valves can be there and they will create a closed system. What big box stores do or don't do will likely vary from place to place, but when I had to install my expansion tank after I put in my PRV, I went to Lowe's. The people in the plumbing dept. had never heard of such a think. One guy tried to sell me a pressure tank for a well! I then went to HD. They had them in stock, two sizes even. Lowe's still doesn't stock them, but they do sell PRVs. Draw your own conclusions.

pressure regulator valve (PRV) - Do I need an expansion tank for California regison

Please correct me if I am wrong. The pressure regulator valve sits outside the house.
Here is a picture, If I have a pressure regulator, Do I need an expansion tank with a water heater installation.

I have seen over 12-13 homes in my area, however, no one has heard of expansion tank.


Thankss.

Today's gas water heaters on average have a higher BTU than was true in the past. That higher BTU can create an expansion problem where one did not previously exist. If by coincidence, someone opens a tap, even briefly, during the heat cycle, that would also release the pressure. But the possiblitly of squeeezing the relief valve is definitely there.

jimbo said:

Today's gas water heaters on average have a higher BTU than was true in the past. That higher BTU can create an expansion problem where one did not previously exist. If by coincidence, someone opens a tap, even briefly, during the heat cycle, that would also release the pressure. But the possiblitly of squeeezing the relief valve is definitely there.

Click to expand...

The BTU of the heater is not really the issue. That would only cause the pressure to go up quicker but even with a lower BTU burner the pressure will still rise in a closed system.

The higher the temp rise and the amount of water your increasing the temp on is what matters.

Hackney plumbing said:

The BTU of the heater is not really the issue. That would only cause the pressure to go up quicker but even with a lower BTU burner the pressure will still rise in a closed system.

The higher the temp rise and the amount of water your increasing the temp on is what matters.

Click to expand...

Yes....but....

The heated water expands into the piping by convection...and to some extent there is heat loss in the piping that slows down the expansion. THis is just anecdotal, but 15 or 20 years ago, the need for an expansion tank rarely came up, and in recent years it does.

jimbo said:

Yes....but....

The heated water expands into the piping by convection...and to some extent there is heat loss in the piping that slows down the expansion. THis is just anecdotal, but 15 or 20 years ago, the need for an expansion tank rarely came up, and in recent years it does.

Click to expand...

The burner size has nothing to do with needing an expansion tank or not. Its the amount of water and the temp rise of that water in a closed system that dictates the amount of expansion. The heat loss of the piping is not considered

Edit: Burner size/BTU only would cause the same pressure to build quicker,but in a closed system all roads meet in the end.

I believe that the reason expansion tanks were scare 20 odd years ago was that many homes did not have regulator valves (or other check valves).

Here's a true story relevant to this discussion...
In the late-70's, my parents purchased a custom-built home in a "high-end" neighborhood. It had no PRV and no expansion tank. A couple of years later, the T/P valve on the water heater kept popping. The water pressure was measured and was too high (don't know if it had always been high, or if the water company did something to increase the pressure). So a PRV was installed (as well as a new T/P). But no expansion tank was installed (this was before big box stores, the internet, etc, so no one was the wiser). A number of years later, the water heater burst. A new water heater AND an expansion tank were installed.

My recommendation: Always install an expansion tank, whether or not the code requires it. They add little to the cost of the installation, but offer significant benefits.

Unless that pressure regulator has a bypass, my understanding is that the UPC requires an expansion tank. I haven't seen any tanks in this area, so either the common regulators used here have it, or the inspectors don't care (probably the inspectors).

My Dad's water heater PT valve has always leaked since the 60s (replaced numerous times). He has 140 psi+ from the street (and a regulator, of course). When I read the code book the first time, a light bulb lit up!

The smaller the heating source, the slower the reheat is, the more time your system has to relieve that pressure gain through leaks...toilet valve, or a leaky valve anywhere. The quantity of water pushed back if you have an open system during heating isn't much. Don't know enough about the innards of a meter design to know if it actually will run backwards or not.

Like external hose bibs now require vacuum breakers and sprinkler systems backflow preventers, many utilities are installing check valves in their part of the system. An expansion tank helps keep pressure more constant, and at least theoretically, would put less stress on all of the plumbing, including the WH.

Can someone find for me in either the IPC or the UPC where is specifically says that if you don't have a check or BFP on the main then you don't need an expansion tank. I can't find that anywhere. I used to get that all the time from plumbers that because the water supply is a private well then the well tank will take care of the expansion. And.....it will but......the code does not make that distinction. Also, why the big deal here. If I'm installing the heater I would like to sell the tank also. I sell and install tanks and I make money doing it.