Expansion Tank Question

[senoiasummer]

I have two 50 gallon water heaters in series.   Looking that the charts I have seen for expansion tanks (put out by mfgs) it shows if you have 100 ga water heaters and normal inlet pressure you should use a 4.5 gal tank.   However, currently there is a smaller tank installed.   I just replaced the water heaters and now am wondering, shoudl I go with the 2.5 gal or 4.5gal expansion tank.   Is there a danger of putting to big an expasion tank on?

[RegUS_PatOff]

...  Is there a danger of putting to big an expasion tank on?

I'm not an expert, but I think it's OK

It may be better to put a 2.5 Gal on each tank, if they're not near each other.

[senoiasummer]

The water heaters are right next to each other and are in series, connected by about an 18" piece of CPVC.

[Cactus Bob]

city or well water ?

 

if city water you need a tank somewhere in the system , or at least you should have (they say) . You can never go to big , it will just take up more room

 

well water , you already have an expansion tank , the tank on your well pump

 

 

to be honest , i have city water , and no tank , most people don't . never seen a pipe or water heater tank burst because of a lack of one

[RegUS_PatOff]

One other note:

you would certainly need an expansion tank if your water heaters don't have a pressure relief valve,

OR if your incoming water line uses a pressure reducing, or back-flow prevention valve.

[Cactus Bob]

All our water systems have a back flow check valve , but still have no pressure tank

we all have pressure valves installed on water heaters factory installed , but i have never seen one blow off

I would think we should have a problem too , but all these years , no problems at all

 

i think the OP , has a pressure tank because of the TWO water heaters , that's a lot of expansion going on

[RegUS_PatOff]

http://www.youtube.com/watch?v=_tVhxFz5GpU

[Cactus Bob]

no thanks , no interested in a propaganda video put out by an insurance co , produced to instill fear in order to sell there reassuring product .

 

I deal in a reality that has been seen by my own eyes , my fathers and my grandfathers life experience repairing heating , plumbing , ac , appliances going back to 1920

my grandfather only spoke of one hot water tank explosion in his lifetime and it was early on

 

it has only been the last 15 years or so that new homes have expansion tanks.

Around 1960 pressure regulators started having check valves

so all those houses in between should be blowing off there foundations by now , and there not

 

I do not argue that some sort and size of tank is needed to capture any expansion , but i feel the small size of the OP's tank is a result of following codes at a minimum and covers the real need .

[senoiasummer]

Well, we are on city water, the heaters do have pressure relief valves (dont they all?), and there is a backflow/regulator on the inlet, which I think has been code where we live for many years.   The Ex-plumbers that are now working at the Mega Home improvement stores tell me any time you replace your water heaters, you should replace your expansion tank.  I was skeptical, figuring they were just trying to increase the bottom line sales price.   The water heaters I replaced were 13 years old.  One, the "downstream" tank (i.e., the second one in the series) had began to leak from the bottom of the tank.   What I have noticed, since I replaced the water heaters (and actually, started before I replanced them) is that the toilet on the first level of the house, regularly has brief peirods where it "runs" for a few second and then turns off.  

 

 

In my (admittedly simple (when it comes to plumbing)) mind, this is a symptom that the HW heater is causing pressure back into the supply line and this is how this pressure is escaping ..... I dont know, but for $50 it seems like a good "insurance" policy.

 

Not sure I agree with the Mayhem commercial or not, but I like watching them.   Clever advertising, and pretty entertaining.

[bbealing]

A bigger expansion tank will not hurt anything but you probably can get away with a smaller tank if you want.  My advice is to properly support the tank.  You stated you used CPVC pipe- that piping doesn't provide enough support.  When an expansion tank gets water logged, there's a lot of weight there that better have some support or you will break CPVC piping.

 

Do you need an expansion tank?  That depends.   Cactus Bob has it right-your tank(s) will not blow up if a pressure relief valve is properly installed-they are installed by the manufacturer to prevent that from happening.  There are a lot of water heaters installed that have no expansion tank installed-even when there is a check valve on the incoming system.  Why?  I can't answer that and have not been able to find anyone who could give an acceptable answer.  I've seen situations with multi-townhouses where 19 of the houses didn't need an expansion tank but one of the units in the middle needed it.

 

You know you need an expansion tank when:  the incoming water pressure fluctuates while sitting dormant (pressure gauge reading on house side of check valve) or you need one when the water heater's pressure relief valve "seeps" for no apparent reason.

 

Senoriasummer:  Your toilet issue is not related to your water heater....it is a slow leaking toilet flapper inside the tank.

[Daveb1972]

Guys,

sorry to dispute, but if your municipality has meters, AND check valves, you MIGHT be ok, until they raise the water pressure, I've seen tanks with bulged tops 3-4 times, and found the T&P doesnt open in some of them. The manufacturers have started to refuse warentee unless you install an expansion tank and PRV. I still avoid it in most installs, but I have seen it first hand...have pics somewhere I'll try to find them....

[telefunkenu47]

Within the trade there has been some discussion about the use of expansion tanks and premature failure of weleded seams. The consensus is that a properly installed expansion tank will increase the life span of a water heater by 30 percent or more. The industry has been lobbying to make it mandatory code for quite some time now, but to no avail. I personally prefer the least amount of code requirements possible. The code has gone from the sublime to the ridiculous. 

Back when municipalities began to require the installation of backflow preventers they found that a percentage of water heaters began to seep water from the pressure releif valves. Primarily in smaller homes with less pipe volume to take up the slack as far as the increased volume of water, which as we know is non compressable. personally, I think its good insurance what with the price of indirect fired water tanks now at the 1000 dollar mark and up. I install dielectric unions and expansion tanks all around. Bigger the better.

[RegUS_PatOff]

... a properly installed expansion tank will increase the life span of a water heater by 30 percent or more.

but the life-span of an expansion tank is a few years, and there's no indication when the bladder fails,

unless maybe you have a pressure gauge installed, and keep an eye on it.

[telefunkenu47]

very true Reg. Webstone makes a very cool valve setup part no 41672 which makes it easy to drain and replace an expansion tank. It costs around 15 bucks and I use it any time I install an expansion tank. I generally see 10-15 years on heating expansion tanks(12-18psi0 and 7-10 years on ones made for domestic water. Obviously it would depend on waater hardness and system pressure.I use Therm X Trol st-5 for residential apps. I think Ive beaten this horse to death. Good luck!

[Daveb1972]

Knock test is easy and cheap and "nearly" flawless at diagnosing failed diaphragms.