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Water Heaters – Expansion Tanks

Hot Water Heater Expansion Tanks

Virtually, every modern plumbing code requires the installation of an expansion tank on hot water heater installations. The reason is simple. Water expands when heated. This extra volume of water needs to go somewhere. Before the widespread usage of backflow preventers, check valves and pressure reducing valves, this expanded water simply pushed the cold water back into the city water main. If your house has one of the above mentioned devices, you could have problems. These devices prohibit the flow of water from your house back into the public water system.

Without an expansion tank, the expanding water can cause your hot water heater to possibly fail because of the increased pressure. This pressure can cause serious life threatening problems as well, if you heat your water with natural gas or propane. The water heater tank can collapse around the internal flue and cause carbon monoxide to enter your home. It is serious business.

Expansion tanks are really simple devices. They contain compressed air and a special rubber bladder. When your hot water heater turns on, the water within your piping system begins to expand. This expanding water enters the expansion tank. Eventually, hot water is drawn from the system thru a faucet and the expansion tank releases the extra water into the piping system.

Expansion tanks come in various sizes. The size you need depends upon two very important variables. You need to know the capacity in gallons of your hot water heater and the water pressure of your house piping system. The capacity of your hot water heater is stamped on a label or a plate on the side of your hot water heater.

Water pressures within municipal water systems vary widely. Here in Cincinnati, water main pressures vary from 50 pounds per square inch (PSI) to over 200 PSI within a distance of a mile! This same thing may be true in your city. People with cisterns or wells control their own system pressure thru the use of electric pumps.

It is easy to determine your incoming water pressure. Many plumbing supply houses sell a little gauge that attaches to any faucet which has garden hose threads.  Or if you like, you can call your local water department. They will possibly send a technician to your house. This person has very accurate gauges which will do the same thing.

Once you have this information, visit a local plumbing supply house that sells these tanks. They will be able to provide you with the proper sized tank to suit your needs.

Be sure to follow the directions that are packaged with the expansion tank. It only takes a few moments to read them. This will insure that your tank will function properly.

If you install a pressure reducing valve to control water hammer, be sure to buy one with a bypass feature. Without this, your water heater will begin to malfunction. You will see water dribble out of the pressure/temperature safety valve without a doubt.

The reason lies in the fact that heated water expands. Without a pressure reducing valve, this expanded water can easily go right back outside to the water main. Low quality or malfunctioning pressure reducing valves block this backwards flow of expanding water.

An inexpensive expansion tank installed on the cold water side of your hot water heater will solve this problem. The tank absorbs the expanding water and then releases it once hot water is drawn from the hot water heater. They are simple yet effective devices.

Installing an Expansion Tank

The first thing you need to do is to size the expansion tank according to the size of your hot water heater. The tank manufacturers make this easy. All you have to do is to determine the capacity of your hot water heater. This is always stamped on the side label of the hot water heater. You may have a 50 gallon or 80 gallon or whatever size hot water heater. Take this information to your plumbing supply house to get the right sized expansion tank.

A Simple Tee Fitting

The expansion tank installation requires you to install a simple tee fitting in your cold water supply line. I like to install these on a horizontal run of pipe, not a vertical piece. A vertical piece of pipe can cause undo stress on the connection point between the tank and the supply piping. I always hang my water-heater expansion tank above the horizontal pipe and recommend NEVER to hang it below. However, ALWAYS read the instructions provided by the manufacturer.

The tanks simply have a threaded connection. You will install the opposite type threaded adapter to your tee fitting. Apply Teflon tape or pipe dope to the male threads and screw the tank onto the fitting. To get a tight fit, you may have to use a pipe wrench or a leather belt around the tank. Most tanks come with a place to attach a tightening wrench. Follow the instructions and this can be done in 1/2 hour or less!

Column B192

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24 Responses to Water Heaters – Expansion Tanks

  1. 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?

  2. 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. 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.

      • 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. 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?

    • 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. 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. 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.

  7. 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.

  8. 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?
    https://www.dropbox.com/s/jqz8183ibcqscu4/00153%202.0g%20txp%20failed.MTS?dl=0
    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!
    https://www.dropbox.com/s/236asubytlhgxel/00151%20HAI%20txp%20manifold.MTS?dl=0
    3) Water on the wrong side of the bladder -
    https://www.dropbox.com/s/1tyu8ya8jok63ne/00087%20failed%20bladder.MTS?dl=0
    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.
    https://www.dropbox.com/s/k0s07jc53ec8rja/00238%20txp%20install%20review%20600%20drew.MTS?dl=0
    5) Failed 2.0 gallon TXP tank (from same residence in #4 above) -
    https://www.dropbox.com/s/pb8zanq2pki5p5y/00239%20failed%20txp%20tank.MTS?dl=0
    6) 4.5 gallon waterlogged TXP tank on a commercial installation -
    https://www.dropbox.com/s/jajoswdsalmk3xl/00095%20txp%20tank%20sound.MTS?dl=0
    For a simple view of what we have typically been providing since around 1997 –
    http://hestandassociates.com/txp.jpg
    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!

  9. 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!

  10. 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

    • 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.

  11. Hi,
    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?

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