Water Heaters – Expansion Tanks

35 responses

  1. John Harper
    April 1, 2012

    You state one needs to know the capacity of a water heater ( in my case 75 gallons) and the water pressure (in my case 55 pounds per square inch) to calculate the size of pressure tank (2.00 gallons in my case) and the air pressure induced at the top of the pressure tank, I assume. So what air pressure am I to apply to a 2.00 gallon pressure tank to be safe and not sorry, given the parameters shown above?

    • Tim Carter
      May 23, 2012


      You simply look at the table provided by the expansion tank mfrs. Simple.

  2. Ian deCone
    April 29, 2012

    I have been getting pulsating water periodically. I am thinking my expansion tank may have failed. I have a pressure regulator on the cold side of the line near where the water enters the house. My expansion tank is on the outflow side of the hot water heater and hung under the line - two things I believe were ill advised per the guidance in this blog. Do these tanks fail? I am wondering if mine has failed due to the placement and way it was installed perhaps made it wear out prematurely. Thoughts? Thanks - Ian

  3. Tim Taraska
    June 4, 2012

    Had a new hot water tank installed last summer and since I blow all of the water out of my system for the winter in Vermont, I was suprised that the expansion tank ruptured on the bottom. Kind of a big mess when I turned on the water supply this spring and flooded the downstairs below the ruputured expansion tank. This has never happened before ( more than 25 years of draining my system). I suspect that it was a faulty expansion tank because I was getting water from the pressure relief valve during the weeks following installation.
    Now I'm thinking my old expansion tank was mounted Input down meaning it looked upside down but the new installation is opening up like a bottle. This might be why water remained in the tank and made it rupture ? Finally my question - Should I re- orient the expansion tank with the inlet down or is that not a good idea ? I just paid $55 for this new expansion tank and now I am not getting water from the pressure relief valve as I did with the old bad ruptured tank. Thanks in advance for any help.

    • Tim Carter
      June 6, 2012

      I see MANY tanks installed incorrectly. The inlet into the expansion tank should ALWAYS be pointing to the floor so water will drain out of the tank.

      • Tim Taraska
        September 1, 2012

        That's what I figured. I guess the plumber did not realize that I drain my system for the winter and if the house was heated all year there probably would not have been a problem. I will have to flip it over this fall before I drain the system. Thanks for the reply

  4. Larry Davie
    October 22, 2012

    I need to know the truth about expansion tanks; I recently contacted two plumbers and got two different answers. The problem I am having is I have little black deposits coming from my hot water faucets. I called my insurance company to see if the tank was covered, they in turn sent out a plumber to check out the problem, which he said it was the expansion tank improperly mounted or should I say incorrectly placed. He informed me that the tank should have been placed on the right (cold valve) instead of the left (hot valve). I contacted the builder and he in turn gave me the person who installed the expansion tank. After contacting him and explaining to him the problem he insisted that it was improperly installed and it didn’t’ make a difference which side it went on; and all that was needed was for me to drain the hot water heater and replace the expansion tank and everything would be fine. Now, the plumber that was sent by the insurance company said the hot water heater needs to be replaced installed correctly or the problem would continue. Everything I have read online tells me the tank should have been installed on the cold valve. So which should I believe and what is the best course of action for my problem?

    • Tim Carter
      January 6, 2013

      Larry, your question requires lots of typing, plus I have some questions for you so I can give you the correct answer(s). I only do pithy answers here in the comment section. If you want to protect the investment you have in your house and not waste time or money *hoping* you make the right decision, you should talk to me on the phone for just 15 minutes. It'll be the best investment you've ever made in your home!

  5. Mark
    February 8, 2013

    I think the tank should be pre-pressurized by you to match the input water pressure in your system. Using a manual tire pump is the best way to increase the presure. You should not assume the tank has the correct air pressure from the factory for your home.

  6. Charlie Clifton
    March 14, 2013

    Our home has a circulating pump on the water heater with a timer on the pump , works great instant hot water on the first floor to all fixtures baths and kitchen with the loop system. The problem is the second floor bathroom takes at least 1-2 long minutes to get any hot water at all in the shower or sink.
    I noticed the hot water supply for the 2nd floor bath is tee'd off the first floor return loop about 10' from the water heater. Why does it take so long to get hot water? The 2nd floor bathroom is only about 25' from the first floor outside water heater. I also notice there is not a check value on the loop pipe in front of the circulation pump. Please help if you can any suggestions.

    • Tim Carter
      April 1, 2013

      Charlie, Walter, this is what my 500-Second Consult is all about. Click the Shop icon at the top of the page!

  7. Kevin
    September 30, 2013

    How can you tell if your expansion tank needs to be replaced?

  8. Jim
    September 29, 2014

    My house is 11 yrs. old and I was just told by a plumber that the hot water heater expansion tank should be changed since it is that old. Is that correct? I have not noticed any problems but will be glad to change it if necessary to avoid damage to my water heater or plumbing system.

    • Tim Carter
      September 29, 2014

      So my column above didn't convince you as to why you need one? I need to do a better job of writing!

  9. shana
    October 19, 2014

    Its safe to install bigger expansion tank than smaller if we cant check pressure

    • Tim Carter
      October 19, 2014

      Do what it says at the tank manufacturer's website.

  10. Gary Charles
    January 16, 2015

    Hey Tim – Gary here in Raleigh, NC. I have been a commercially licensed plumber since the early 1990's - and have a few comments to share about “thermal Expansion”. 1) The whole sizing aspect, per what's on most every TXP box we have seen - is actually WRONG!
    To better understand this; one has to know that the IPC (International Plumbing Code) states that 80psi is the maximum pressure allowed on a plumbing system (https://law.resource.org/pub/us/code/ibr/icc.ipc.2009.html 604.8). As a protection device to keep the water heaters from becoming an explosive vessel – the T&P relief valve on the water heater operates (or, relieves water) at 150psi or 210F as a safeguard. 2) The MFG’s (with their sizing targets) appear to be following the premise of meeting “minimum standard compliance” – so long as their not any evidence of discharge at the T&P valve outlet (or, 150psi) – which would be 70psi in excess of the 80psi maximum. And in reality, if 80psi is a maximum target, we would prefer to say or understand that at a 60psi delivery (adjustment of the PRV) – it would give the home’s plumbing system a 25% cushion of safety against “knocking on the door” of the IPC’s “maximum”.
    Noticing that your followers were asking about sizing – maybe they could appreciate the following link from Union County, NC Inspections Department (which BTW – is the “only county in NC” who’s Inspection Department requires a sizing criteria out of the 100 counties in NC - LOL). http://www.co.union.nc.us/pw-calculator.html
    If you use this calculator, and your target is to have a 60psi static pressure; and your “not to exceed” maximum pressure is 80psi – a 2.0 gallon TXP (thermal expansion tank) would only accommodate a 28 gallon water heater!
    A couple of things to note – these tanks have to comply with the NSF (National Sanitary Foundation); which only allows potable water to be in contact with a butyl rubber compound (the “old school” black rubber that is now found as chemically sensitive to the chloramines) – which means that the bladder (if optimally installed) will be chemically failed within 5 to 7 years; and warrant replacement. When it fails, there will not be any bells, alarms or whistles to give you indication to take action. Also, when the bladder fails – the tank will become waterlogged and weigh (@ 8 pounds to the gallon) as much as 16 pounds plus the 3 pounds on a 2.0 gallon tank; or, as much as 37 pounds on a 4.5 gallon tank – which may cause stress and break off at the spud from the tank.
    You made mention of using a strap wrench to tighten the tanks. Most MFG’s say “do not” use the tank to tighten, use a wrench and the hex of the spud to do the tightening. This is due to the weld of the dissimilar metals (typically stainless steel to carbon steel) and they do not want the interior finish to crack or blemish, which would cause the tank to experience premature oxidation at the weld.
    You, and the MFG’s, say to simply install the tank into an FIP adapter. Great! But, each MFG also says to test the tank annually; to “test the tank” you have to turn off the water supply to the water heater – if the TXP tank is located downstream of the supply valve and on the hot water piping. “Remove” the pressure on the line serving the TXP tank (drain the water). Measure the air pressure at the Schrader stem with a tire gauge – “Oh” make certain that you know what the plumbing pressure is; and make certain that the air pressure of the tank equals the static pressure on the plumbing system. And, to check the bladder for failure – how are you going to do this, if it is rigid to the piping system? If it were free to have movement – you could weigh the tank (with your hand) to check against it being waterlogged. If it were free to have movement – it could be shaken to listen for water on the WRONG side of the bladder. If it had an independent isolation valve; and bleed valve (port – or, boiler drain with MHT) it could be independently isolated, drained and a pressure gauge could be easily connected. WOW – service!
    Below are a few Dropbox links –
    1) how to test the tank for a waterlogged condition, using a quarter?
    2) Amtrol 4.5 gallon tank with independent TXP isolation valve, secondary pressure port that is also used a bleed down valve for the TXP tank during testing, the dual MAIN isolation valve manifold with PRV valve and front-end MHT port. We leave the manifold spread between the two valves – so that we can later install a front-end 10 micron (washable) micro-pore sediment filter and a dual cartridge active carbon 5 micron polisher. Having the two valves makes servicing the filter relatively easy!
    3) Water on the wrong side of the bladder -
    4) Interim suffice to install a TXP tank, isolation valve and dual serving pressure port (MHT) and bleed valve – done as a temporary means until we can schedule a manifold assembly installation, where we will reuse this same tank and some of the parts.
    5) Failed 2.0 gallon TXP tank (from same residence in #4 above) -
    6) 4.5 gallon waterlogged TXP tank on a commercial installation -
    For a simple view of what we have typically been providing since around 1997 –
    As for Jim (#8) – and you not being able to convince him – typically, one of the toilets stays in a state of disrepair (high pressure relief) and it becomes the “saving vehicle” for the home’s plumbing system. And sooner or later – this toilet will fall victim to a Saturday “honey dew list” – at which time the home will now become “tight” and during the next heating, the thermal expansion process will occur – hopefully, to “take out” the next weakened toilet fill valve; before it damages the water heater or causes a plumbing failure within the plumbing piping. If your home or building has a DCV (dual check valve) – one of these - http://hestandassociates.com/cpg1426/thumbnails.php?album=134 ; and you have a water heater; and your home is “tight” (not having any leaks) – your home will experience a pressure curve something like this – http://hestandassociates.com/cpg1426/thumbnails.php?album=8 .
    Hope you find the information insightful and enlightening. Regards!

    • Rob Ross
      June 21, 2016

      SPOT ON!!!! THANK YOU Gary Charles. I have had some good chuckles reading this forum and also a lot of raised eyebrows!!! Glad someone else out here knows what is really going on!!!

  11. Steve C.
    March 18, 2015

    According to "George Carlin". It's a "Water Heater" not a "Hot Water Heater". He stated if the S(*t is already hot why do you need to heat
    it. Words from a wise man!

  12. Natalie payne
    March 19, 2015

    I'm am buying a hud home and need an inspection. I was informed that a water pressure test was done and there is no pressure. This house does not have a water heater in it. Would this be why I received this result

    • Tim Carter
      March 19, 2015

      If you have no pressure, that means you have no water. If you have low pressure, it could mean you have a leak in the main water line or obstructions in the water pipes or faucets.

  13. Steve Renfrow
    April 10, 2015

    I am installing two 50 gallon water heaters in series. Should I put a thermal expansion tank on the cold side of both heaters or one larger expansion tank on the first cold water input?

    • Tim Carter
      April 10, 2015

      You only need one tank SIZED for the quantity of hot water you have. Pay attention to the sizing tables provided by the tank manufacturers.

      Install the tank up side down so water pushes UP against the bladder.

      • Steve Renfrow
        April 10, 2015


  14. Brian
    May 1, 2015

    Tim, On April 29th 2015 in Cincinnati, I was charged $181 for a 2 gallon expansion tank, 18" of new copper plumbing, shut-off valve,and installation. Was that an excessive amount?

    • Tim Carter
      May 2, 2015

      Not at all! Did you go to Amazon.com to see what the expansion tanks cost, the copper and the valve?

      You got paid for 8 hours when you used to work, shouldn't the plumber? He's got to drive between jobs and to get supplies. Who should pay for that?

      What do you think it costs to operate a truck 8 hours a day including all depreciation, gas, oil, maintenance, tires, insurance, etc.?

      What do you think it costs per hour to hire a skilled plumber?

      Did you know that employers have to MATCH the employee's FICA and Medicare and Obamacare deductions on a paycheck?

      Do you have any idea what Ohio Workman's Comp payments are per hour for plumbers?

      Do you have any idea what it costs per hour to operate the plumber's business - his office / shop?

      Do you have any idea what it costs the plumber for general liability insurance per hour?

      Do you have any idea what the plumber pays the person who answers the phone?

      Do you want the plumber to make a small amount of NET profit so he can reinvest it in his business so when you need him again he's there?

      Should I keep asking questions?

      I was a small business person for years - heck, I still am - and people who've never been in business for themselves have no idea all of the hidden costs there are in running a business.

  15. Kathleen Hogan
    August 28, 2015

    Just wondering I had a burst pipe recently and when the plumber came back to sort he replaced the expansion tank with a bigger one and put in on the left side of the pipes. The other one was on the right hand side and to me seemed to be installed in a lying down position if you know what I mean The new tank is in an upright position with the pipe at the top of the tank. Does an incorrectly installed tank cause a vibrating sound from the heat unit.

  16. Tom van Thiel
    September 13, 2015

    By shutting off the water on the upstream side of the expansion tank, then opening a hot water faucet downstream and allowing the tank to blow down, I measured a gallon of water blown out of the 2-gallon expansion tank. This suggests that the charge pressure is too low. Since the faucet was about 6 feet above the tank, if the bladder were ruptured it would have blown down to roughly one atmosphere (14.6 psi) plus 6 ft multiplied by 0.44 psi/ft, or 17.24 psi absolute (2.64 gage), which would correspond to roughly 34.5 psi absolute (19.9 gage) prior to blowdown, assuming a constant temperature expansion of the gas in the tank (so that pressure times volume is a constant). (Constant temperature is a good approximation if you wait long enough for the blowdown to complete.) Since the pressure regulator is set for 50 psi gage (64.6 psi absolute), I conclude that the tank was not initially at 19.9 psi gage, and did not blow down to such a low pressure, therefore the bladder is intact and the tank merely needs to be pumped to a higher pressure.

    This method beats tap-testing with a coin.

  17. Tom van Thiel
    September 13, 2015

    The foregoing assumed that all of the water was expelled from the expansion tank, leaving 2 gallons of gas at the lower pressure. That is not necessarily true. If some water remained, the gas pressure could have dropped from 50 psi gage to 2.64 psi gage. In fact, with the tank mounted horizontally (as it is) and the bladder ruptured, it would have been half-full of gas and half water at end-of-blowdown, and at 50 psi gage the gas volume would be 17.64/64.6=0.27 gallons, so that roughly 0.73 gallons water would have been expelled. In addition, any gas trapped elsewhere in the system (such as at the top of the water heater) would contribute to the volume of water blown out of the system. All that can be said is that the volume of water blown out is suspiciously close to half the expansion tank volume, so may represent a ruptured bladder. This can be detected by pumping air into the expansion tank, with water shut off upstream and open downstream, to see if the charge pressure is (or can be raised) above ~3-4 psi gage. (If not, the bladder is ruptured.)

    Finally, a pinhole leak in the bladder would have still another characteristic, but should still be detectable by pumping-in air, then waiting to see if the charge pressure holds.

    Regarding the coin tap test, the vessel is probably too rigid for the human ear to distinguish between wet and dry inner surfaces. Tapping on different points would excite the various shell-modes differently, yielding different tones and easily deceiving the ear.

  18. Brian Schutz
    September 24, 2015

    I have purchased a 7 year old home. It has 2 separate hot water heaters; One in the garage (main level) and one in a utility closet on the 2nd floor. The main floor (garage) water heater has an expansion tank, but the 2nd floor one, does not. Is this sufficient? Or, should there be an additional expansion tank on the one upstairs as well?
    Thank you!

  19. Mark C. Hein
    November 1, 2015

    Hi Folks,
    I have installed 2 hot water heaters since we moved into our house in 1983.
    After replacing the "original" heater (which was approximately 30 years old) I knew I was going to have to replace it shortly after the warranty had expired. WHY? Because of several factors... Cleveland, Ohio's water is very "hard", the suburb we live in is the first (along with the neighboring suburb) are the first off the water reservoir at 140 lbs. pressure!
    Obviously today's water heaters are simply not structurally/materially as well made. So on, again, the first installation I installed a pressure reducer since the safety valve was pushing a cup of water every night.
    On this last replacement (1/8/2007)I HAD to add an expansion tank and have had NO such problems since.
    Not only that but the tank's 5 year warranty is now nearly 3 YEARS over the limit and no problems.
    Of course again I feel that the actual material and structure of the tanks of the past 40 years are at the REAL heart of this problem. Why build the best when you can sell a whole new on every 5 years?!!!

  20. Jane
    November 1, 2015

    re: expansion tanks Lived in house 28 yrs on slab. House is 38 yrs. 4th electric water tank installed May 2014. Never have had an expansion tank. Am I safe?

  21. Eldred Coot
    November 1, 2015

    Never knew about these tanks. Here in the hinterland the plumbers have no idea what this is. Things are different than in the big cities.
    Glad I now know and will install one when I get a tank.

  22. Steve
    July 26, 2016

    I have a problem with some of these comments based on something I realized last night about 1/2 way done. Amtrol instruction specify that the hot water heater expansion tank be vertical with the connection up and the Schrader valve down. If you put it the other way you have made a double bladder because air gets trapped between the bladder and the supply side. The tank must be installed per their instructions so the bladder is lower than the supply line and any air in the tank or expansion lines can flow back to the supply side and be pushed out when a faucet is opened.

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