# Expansion Tank for Water Heater



## jar546 (Nov 28, 2019)

Do you agree with his opinion?
The opinion kicks in towards the end after the 10 minute mark.


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## ICE (Nov 28, 2019)

I disagree with the willy-nilly installation of an expansion tank.  I have corrections for the furnace.

Minute 1:35 is a blast.


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## mark handler (Nov 28, 2019)

ICE said:


> I disagree with the willy-nilly installation of an expansion tank.  I have corrections for the furnace.
> 
> Minute 1:35 is a blast.


Thank for posting, that was cool


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## fatboy (Nov 29, 2019)

I actually watched that episode of myth busters......flippen cool. 

The expansion tank, not until you have a check valve in the system somewhere. Some water providers require a incoming check valve, so yes, need the tank, otherwise...not....


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## jar546 (Nov 29, 2019)

So far for me, every single municipal water company in every jurisdiction, in every state I've worked in required a backflow preventer for the house so I am not sure where an expansion tank would not be required.


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## fatboy (Nov 29, 2019)

Well.........not here.

Been the single source water provider for over 140 years.


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## fatboy (Nov 29, 2019)

And without a check valve ahead of the premise, pressure tank would not be required.


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## Inspector Gift (Dec 2, 2019)

Our City water meters have internal check valves, in addition to high water pressure that requires PRVs at most homes.   Yes, expansion tanks are essential.   
Last month during the initial the final inspection of a show home in a new development, We noticed that there was water on the garage floor coming from the water heater.   And Yes, it was due to high pressure (123#).   The plumber had failed to install a PTR valve and an expansion tank. The plumber installed both and the problem was corrected.


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## ICE (Dec 7, 2019)

jar546 said:


> So far for me, every single municipal water company in every jurisdiction, in every state I've worked in required a backflow preventer for the house so I am not sure where an expansion tank would not be required.



Well what with Florida being at the bottom of the country I suppose that the water pressure would be up there.


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## Mike Hutchinson (Dec 12, 2019)

I also watch the myth busters and yeah, some water providers  require an  incoming check valve that's when you'll need the expansion tank.


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## Michael.L (Dec 12, 2019)

Expansion tanks are fairly inexpensive and easy to install at the time the water heater is installed. I see no reason not to install one with every water heater, even if there is currently no (known) backflow preventer or PRV. You never know when the utility company will decide to upgrade their meters and suddenly you have a check valve in your system.


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## jar546 (Dec 12, 2019)

Michael.L said:


> Expansion tanks are fairly inexpensive and easy to install at the time the water heater is installed. I see no reason not to install one with every water heater, even if there is currently no (known) backflow preventer or PRV. You never know when the utility company will decide to upgrade their meters and suddenly you have a check valve in your system.



Makes absolute perfect sense.


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## ICE (Dec 12, 2019)

jar546 said:


> Makes absolute perfect sense.


That’s why we don’t do it.


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## Paul Sweet (Dec 13, 2019)

Does the water heater also need a separate expansion tank if you're on a well and have a pressure tank?


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## Michael.L (Dec 13, 2019)

Paul Sweet said:


> Does the water heater also need a separate expansion tank if you're on a well and have a pressure tank?


As long as you KNOW there are no check valves (including check valves built into other devices) between the water heater and the well system's pressure tank, then no, you do not need an additional expansion tank.


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## classicT (Dec 13, 2019)

Paul Sweet said:


> Does the water heater also need a separate expansion tank if you're on a well and have a pressure tank?


Is there a check valve to prevent backflow into the pressure tank?


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## jar546 (Dec 13, 2019)

Ty J. said:


> Is there a check valve to prevent backflow into the pressure tank?



Every well that I have inspected had a checkvalve in the system to prevent backflow to the well.


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## classicT (Dec 13, 2019)

jar546 said:


> Every well that I have inspected had a checkvalve in the system to prevent backflow to the well.


Agree. But if there is not a check valve downstream of the pressure tank , then I'd use some judgement and exempt it.

The pressure tank is a expansion tank, only about 10-100 times larger.

**Update** - Larger and it has a full diameter pipe connection (3/4" vs 1/8" for saddle tap expansion tanks)


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## Michael.L (Dec 13, 2019)

jar546 said:


> Every well that I have inspected had a checkvalve in the system to prevent backflow to the well.


Every well system must have a check valve upstream of the pressure tank, otherwise the pressure tank would discharge back into the well once the pump stopped. For a submersible pump system, the check valve is typically on the drop pipe just above the pump.

The question is: Is there a check valve downstream of the pressure tank? This would be less common, but certainly possible.


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## Michael.L (Dec 13, 2019)

One other thing to consider regarding whether or not to install an expansion tank. If the homeowner (or whoever) shuts off the cold water supply valve that feeds the hot water heater, but forgets to also shut off the water heater thermostat, then there's a risk of the tank bursting if there is no expansion tank.

This is another reason why I advise simply installing an expansion tank for every tank water heater. ALWAYS install the expansion tank between the water heater's cold water supply shut off valve and the water heater.


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## Rick18071 (Dec 13, 2019)

Do you need a water-hammer arrestor if there is a expansion tank?


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## Michael.L (Dec 13, 2019)

Rick18071 said:


> Do you need a water-hammer arrestor if there is a expansion tank?


Water hammer arrestors should be installed on the piping as close as possible to the device that causes (or could potentially cause) a water hammer event. Typically, these are valves that close very rapidly like the solenoid valves in a washing machine or a toilet flush-o-meter valve.

The expansion tank is too far away from any of these valves to absorb the shock wave (water hammer).


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## Rick18071 (Dec 13, 2019)

Michael.L said:


> Water hammer arrestors should be installed on the piping as close as possible to the device that causes (or could potentially cause) a water hammer event. Typically, these are valves that close very rapidly like the solenoid valves in a washing machine or a toilet flush-o-meter valve.
> 
> The expansion tank is too far away from any of these valves to absorb the shock wave (water hammer).



Wouldn't this include a check valve?


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## classicT (Dec 13, 2019)

Rick18071 said:


> Wouldn't this include a check valve?


The hammer arrestors? Nope
The appliance? Some, but downstream of the water heater.


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## Michael.L (Dec 13, 2019)

Rick18071 said:


> Wouldn't this include a check valve?


I'm not sure what you're asking. Water hammer arrestors do not have check valves.

It doesn't matter how many check valves or shut off valves you have downstream of your water heater (technically, everything downstream of your water heater is a closed system when all the faucets, spigots, showers, etc, are off).

The expansion tank MUST ALWAYS be connected by a permanently open pipe to the water heater tank: NO check valve or shut off valve should be placed in the piping between the expansion tank and the water heater tank. The expansion tank is placed on the cold supply side of the water heater so that the tank bladder is not subjected to high temperatures from the hot water, but pressure-wise, the hot side and cold side are at the same pressure.

You can have as many shut off valves and check valves as you want on the water piping (cold or hot) upstream or downstream of the water heater as long as NO valve exists between the expansion tank and the water heater tank. The purpose of the expansion tank is solely to absorb the additional water volume created by thermal expansion within the hot water heater as it heats cold water. Without the expansion tank, that increase in volume due to the water heating has nowhere to go, and since liquids are essentially incompressible, it builds pressure inside the tank. At best, the pressure will cause your T&P safety valve to pop-off to relieve the pressure (but realize that even when the T&P opens, the stress of repeated cycles of 150 psi pressure WILL weaken the tank and cause it to fail prematurely). At worst, you could have a catastrophic water heater tank explosion.


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## Rick18071 (Dec 16, 2019)

Doesn't a check valve  close very rapidly and need a water hammer arrestor?


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## classicT (Dec 16, 2019)

No, a check valve only prevents backflow. It is a one way valve and does not discharge any water.

It is the end appliance that requires a hammer arrestor.


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## Michael.L (Dec 16, 2019)

Rick18071 said:


> Doesn't a check valve  close very rapidly and need a water hammer arrestor?


Swing-style check valves have the potential to create water hammer because, under certain circumstances, the water can start flowing backwards before the swing gate closes. This is why swing check valves are not recommended for home water piping. Spring check valves do not have this problem.


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## Paul Sweet (Dec 16, 2019)

Many moons ago I installed a swing-type check valve between my well and pressure tank after the coupling for the submersible pump came loose and all the water siphoned out of my system.  I learned quickly that I should have installed a slow-closing check valve when I heard a loud CLANG every time my well pump shut off.


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## Rick18071 (Dec 17, 2019)

Ty J. said:


> No, a check valve only prevents backflow. It is a one way valve and does not discharge any water.
> 
> It is the end appliance that requires a hammer arrestor.



Thanks. The code doesn't say what kind of quick closing valve of where it is located to require a hammer arrestor. I also never saw any valve listed as a quick closing valve. To turn off my lab faucet I just need to push it in and it closes pretty quick. Would this be a quick closing valve?


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## classicT (Dec 17, 2019)

Rick18071 said:


> Thanks. The code doesn't say what kind of quick closing valve of where it is located to require a hammer arrestor. I also never saw any valve listed as a quick closing valve. To turn off my lab faucet I just need to push it in and it closes pretty quick. Would this be a quick closing valve?


Depends....

Definition of "quick acting" is subjective. Code is not always clear, is it.


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## jar546 (Dec 17, 2019)

Typically if a valve has a solenoid that closes it quickly such as a clothes or dishwasher or icemaker, etc.  It is quick close and considered quick close.  If you do it by hand, it is not.


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## Gregg Harris (Dec 20, 2019)

Michael.L said:


> One other thing to consider regarding whether or not to install an expansion tank. If the homeowner (or whoever) shuts off the cold water supply valve that feeds the hot water heater, but forgets to also shut off the water heater thermostat, then there's a risk of the tank bursting if there is no expansion tank.
> 
> This is another reason why I advise simply installing an expansion tank for every tank water heater. ALWAYS install the expansion tank between the water heater's cold water supply shut off valve and the water heater.


Wouldn't your temperature and pressure relief that is required take care of this. The bladders is in the expansion tanks can and do fail.


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## ICE (Dec 21, 2019)

Long, long ago I worked for a pool plastering company in the SF Bay area.  At a mountain top property we plastered a water tank that was built for fire fighting reasons to protect a mansion.  I was told that the water pressure was up there.  My hoses swelled to twice their normal diameter.  I could stand them like a flagpole.  Nothing blew.

I was in the laborers union and worked 70+ hour weeks for months on end.  I did it for about three years.


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## Michael.L (Dec 22, 2019)

Gregg Harris said:


> Wouldn't your temperature and pressure relief that is required take care of this. The bladders is in the expansion tanks can and do fail.


The expansion tank is your first line of defense: it _*prevents*_ the build-up of high pressure. The T&P valve is your second line of defense: it relieves pressure after it has *already reached* high levels. You MUST have a T&P valve. You SHOULD have an expansion tank.

Let's say you don't have an expansion tank and only rely on the T&P valve. If the water piping is a closed system (due to a check valve, backflow preventer, closed supply valve, etc.) then every time the water heater fires, the water pressure has the potential to reach 150 psi before being discharged by the T&P valve. Normal water pressure is typically in the range of 45-60 psi, so you are more than doubling the water pressure. Because pressure acts on surface area (pounds *per square inch*), the water heater is subject to a significant amount of force due to the tank's large internal surface area. This repeated expansion and contraction (due to high/low pressure cycles) fatigues the tank, especially at the welds. Note that it can also crack the glass lining, subjecting the steel tank to internal corrosion. All of this can weaken the tank, resulting in early failure.

In a worst-case scenario (closed system, run-away thermostat, malfunctioning T&P valve), the water heater tank can violently explode.

EVERY mechanical device is subject to failure, including the bladder in an expansion tank. That's why regular system inspection and maintenance are important. It's also why it's better to have layers of defense, rather than relying on a single safety device.


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## Rick18071 (Dec 23, 2019)

Where is the requirement for expansion tanks in the IPC?


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## Pcinspector1 (Dec 23, 2019)

2012 IPC 607.3


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