Expansion Tank: Preparation, Pressure and Installation

What is the proper way to install an expansion tank? Many plumbers do not even do it right.
First of all, an expansion tank has an air chamber and a water chamber separated by a diaphragm. The air chamber comes pressurized from the factory, but the pressure is often far below the working pressure of the water system. If an expansion tank has less pressure in the air chamber than the water system, and the air pressure in the tank is not adjusted, the air will compress as soon as the water is turned on, leaving no place for expansion. So the pressure should always be adjusted to the system pressure.
It is also important to consider the manufacturer's installation instructions. How often to people actually read the instructions before installing something? There are some specifics to installing an expansion tank. The tank should be installed on the cold water inlet side of the water heater, down stream of the cold water shut off to the water heater. The tank should be in a vertical position with the water chamber on top, and should be supported by a strap of some kind so that the weight of the tank is not on the pipes. If the system pressure is greater than 80 psi, the water system should have a pressure reducing valve.
Knowing how to install an expansion tank, and installing it correctly is the best way to receive the full benefits that the tank can provide for thermal expansion.

[@itsm3th3b33]

I'm impressed by his one-handed teflon tape wrapping skills.

[@plumber-tom9470]

Thanks. You can do it too!

[@dzinchenko7811]

Awesome video Tom, thank you for sharing your knowledge with us!

[@plumber-tom9470]

My pleasure!

[@actechchris]

Been looking for a video like this. Thank you, 100% answered all my questions!!! 👊🏻

[@plumber-tom9470]

Awesome! Glad I could help!

[@distanceman8147]

I appreciate the video and the work to make it possible. I have the confidence to install a tank safely. Thank you!

[@plumber-tom9470]

No problem 👍

[@garywateridge]

Beautifully explained,so helpful.thankyou

[@plumber-tom9470]

Glad it was helpful!

[@CoffeeWithFred]

This is the first time I have watched your channel/video. Very nicely put together and provided good information in a great format. If any of your other videos are as good as this one, then your channel has a lot of potential. Keep up the great work!

[@plumber-tom9470]

Awesome! Thanks!

[@plumber-tom9470]

I try to keep the quality up on all my videos. Production is time consuming but I think it’s worth it!

[@PhilR0gers]

Simple an to the point. Thanks for that. I'm installing a solar water heater which needs a 6 bar (84 psi) expansion tank for the circulating fluid. Now I know how to prepare and install it.

[@plumber-tom9470]

You got it!

[@wrcurley]

Not sure the disco vibe adds anything, but excellent, simple, to the point. Thanks.

[@plumber-tom9470]

Thanks for the feedback

[@ra_fun3126]

You maked it very clear! Shoot have more views!

[@plumber-tom9470]

Awesome! Thanks for watching!

[@Mustang-Mike]

After buying an Amtrol ST12 expansion tank, the instruction said to install the tank vertical like you mention. I called Amtrol customer service and they said it didn’t matter which way you install it and the instruction sheet needed to be revised. I replaced mine the same way the plumber install it 12 years ago when the house was built, sitting on top of the hot water tank with the expansion tank water inlet facing down.

[@plumber-tom9470]

Interesting. Installation requirements may vary from one manufacturer to another. As long as you do what the manufacturer requires you should be fine.

[@GerardoCruz-vh1zg]

Tks good job 🙏

[@plumber-tom9470]

Welcome 👍

[@AmericanDrainWorks]

thank you. 😊

[@plumber-tom9470]

You're welcome!

[@kellyminnesota]

How close to the hot water tank does the expansion tank need to be located? Can it be 5 or 6 feet away? Also my homes water pressure changes alot through out the day. I have not put a gauge on it but I can see that my yard irrigation heads shoot longer and shorter distances depending on the time of day, so because of this, how should I set the expansion tank pressure, on the high end or low? Thanks for any help, and the great video!

[@plumber-tom9470]

Yes it can be installed a distance from the water heater as long as it is on the cold line. You might consider purchasing a test gauge from a hardware store or plumbing supplier to find out what your pressure is.

[@christopherwright2449]

First time seeing someone paste 1st then tape

[@plumber-tom9470]

Cleaner that way. Doesn’t really matter though.

[@IliadDreyfus-js9oe]

That tape should be snug against the threads

[@thomasfitzgerald2595]

​@@plumber-tom9470Hello Plumber Tom......is it necessary to install a shut off valve after the expansion tank right before the cold line goes into the water tank? And I noticed how you didn't mention anything about how many inches away from the water tank it should be before the cold inlet? I've heard a minimum of 18 but would it be ok if it were a bit closer at say 10 to 12 inches? Would that really cause the expansion tank to not work properly. Im also surprised how you didn't tell people how you can test the pressure of your city water coming into your home by taking a water pressure gauge you can pick up at Home Depot and putting that on the closest outside water fixture where it comes in to the house. Maybe you have a video on that already........

[@plumber-tom9470]

I like it that way because it is cleaner. I don't think it makes a difference.

[@plumber-tom9470]

@@thomasfitzgerald2595 Hello. Thanks for your comment. Manufacturer's may have a recommendation for proximity of the valve to the tank, but I am not aware of any code requirements that way. I don't know that it really matters how close it is to the water heater as long as the expansion tank is on the cold side somewhere. I do have a video explaining how to check pressure. Feel free to check it out.

[@Tom-vy4cl]

Do you have to apply both teflon tape and dope, or just one or the other would be good enough? Also, could you adjust tank air pressure after it is installed? Can one side of pressure in the tank be off by few psi....like maybe up to 5 or 10 lbs?

[@plumber-tom9470]

Hello. Good questions. Teflon tape is what really makes the seal. The dope just helps it along. So definitely apply tape. You can check out my video about that. You should not add pressure to the tank after it is installed unless the water is still turned off. If you try doing it with the water on, your gauge will be reading the water system pressure instead of the air pressure in the tank. Best to adjust the tank pressure before it is installed for the most accurate pressure. You want the pressure to be as close to the system pressure as possible. If it is less than the air chamber will be partially compressed as soon as the water is turned on. If the tank pressure is too high, then it will not allow for as much expansion when needed or it can increase the system pressure. Hope this helps. Thanks for watching.

[@evanhlavaty]

I am on a well with pressure switch set to 40/60. I recently had an iron air injection filter installed which required a back flow valve as well for the regeneration process to be successful. I am now going to install a new hot water tank. I do not have an expansion tank currently, but with the new back flow valve I think one is necessary now. Since the pressure in my system is dynamic with the 40/60 pressure switch should the expansion tank be pre charged to 60 psi to match the top end pressure of my system?

[@plumber-tom9470]

Yes. That is what I would do. That way the expansion tank will be able to take any excess pressures. Frankly, a well storage tank basically is a giant expansion tank, so it is questionable as to whether an expansion tank is needed or not. But since it is a code requirement, I recommend that they be installed.

[@ronh9384]

Good video. Thanks for sharing. Question. Most expansion tanks that I have seen that are installed correctly ( my original was not installed correctly…) are dead headed (only has a cold water pipe going to it) and not mounted on a T fitting like you show… I was looking online after watching your video and found mounting instructions that show it mounted on a T fitting like your diagram. There are of course nothing showing a pressure gauge or shut off valve or any real instructions. Is it ok to dead head the water line into the expansion tank or is it best practice to Tee it off the water line? Thanks for your time! 😊

[@plumber-tom9470]

The connection location of the tank does not matter as much. It just needs to be on the cold water side somewhere, and the tank needs to be supported. As long as that is the case, it can do the job from anywhere it is connected.

[@jeffrohr4795]

The water heater in my 14 year old home is starting to leak so I am replacing it. Can I use the existing expansion tank or is it best to install a new one while installing the new water heater. Also, I have purchased a hybrid heat-pump water heater as it is significantly more efficient (uses a third of the annual energy of a traditional electric water heater). Anything different when installing the pressure tank on this type of water heater. I am assuming the "hybrid" term is that it also has heating rods for times when the heat pump cannot get the water up to proper temperature. Finally, any experience or opinions on the heat-pump type water heater. This one takes the heat out of the ambient air in the mechanical room (as opposed to a separate unit outside as on some models.

[@plumber-tom9470]

Best to replace the expansion tank. They wear out over time. Installation is the same. Just keep it on the cold inlet pipe somewhere. I have heard that hybrid heat pumps sometimes make the house cold. Taking heat from the space around the water heater will effect the overall to some degree

[@jimbo8743]

Tom, thanks for the video. I bought a water pressure gauge, connected it to the water spigot on the side of my house and it is measuring 90 PSI. Is that a very high PSI?

[@plumber-tom9470]

Yes. Code says that your water pressure should be 80 PSI or less. However, sometimes outside faucets are branched off before the pressure reducing valve. You might try to take a pressure reading from inside the house and see if it is the same. You can put your gauge on a washer connection faucet or on the drain outlet from the water heater. If the inside pressure is less, then you are good. If not, you will need a pressure reducing valve.

[@jimbo8743]

@@plumber-tom9470 Thanks man 👍

[@ErsinGokay]

that might be dedicated for sprinkler systems and garden house since majority home appliances will not stand that pressure of over 80 PSI@@plumber-tom9470

[@PrePaidLegalForYou]

For the non-plumbers, this video is discussing an expansion tank for a hot water heater, not for a boiler, correct? Thank you

[@plumber-tom9470]

Correct. However boiler expansion tanks work the exact same. They just operate at a lower pressure.

[@Tbone376]

Hi Tom I have a well with constant water, pressure pump system. About 20 years old. I am getting air every morning at the sinks. Also hammering pips on occasions. This has been going on for a few weeks Do you have Any check list I can follow.

[@plumber-tom9470]

Sounds like a problem with the pressure tank. They are like a giant expansion tank with an air chamber and a water chamber. When the tank goes bad, it makes strange noises and causes problems with the pressure. Could also be the source of air in your lines. I would recommend replacing the tank. When a pressure tank does not hold pressure on a well system, it overworks the pump. Replacing the tank can help the pump to last longer as well.

[@nidalshehahadeh7485]

I have a Watts expansion tank that does not pressurize, I swap the schrader valve even with that it did not want to pressurize, can anything be done or should it be dumped and get another one? this tank have a 1-in thread on it and I have another one with a 3/8 in Inlet on it, does it make a difference? thank you

[@plumber-tom9470]

Time to replace it. The threads are likely 3/4” MIP. You want to stick with that. Smaller threads on expansion tanks are usually used for other low pressure systems and might not have the pressure rating needed for potable hot water.

[@kirkout7366]

My system had 150 psi. The pop-off was leaking ( again). I replace the pressure reducer ( again). Installed an expansion tank. Pressure read at 50psi., after. My pop-off valve still releases. Thoughts?

[@plumber-tom9470]

Once they open, sometimes the T&P valve (pop off) do not seal up again. I have seen that with brand new ones. So you might replace that and see how it does.

[@joeleslie7726]

How do you properly check the air pressure of the tank after it has been installed and in service, especially if you adjust your pressure regulator up or down? Considering the tank pressure needs to match the water pressure I'm assuming there is a procedure to check the air pressure of the tank?

[@plumber-tom9470]

To check the pressure, you have to shut off the water to the system and drain it down. Once the pressure is at zero in the water lines you can take a reading from the tank and see what it is at.

[@captainstress]

@@plumber-tom9470 I have a similar question. I already have a tank installed, but I'd like to get an accurate reading of my water pressure (after the pressure reducing valve). How do I do that without the air pressure in the tank affecting the reading? Do I have to let all the air out of the bladder?

[@plumber-tom9470]

Hello. The tank will only affect the reading if the tank pressure is higher than the system pressure, and even then it is questionable as to how much. But yes, if you want to take the tank pressure entirely out of the equation, then you can release the air, take your system pressure, and refill the tank. @@captainstress

[@rcullen262]

What if I already installed my tank without properly pressurizing it? Can I simply unfasten it, pressurize, and then reinstall, or do I need to purchase a new one?

[@plumber-tom9470]

Yes. You can fill or refill the tank as needed. You don’t necessarily have to take it off. If you shut down and drain the system pressure at a faucet, then you can fill it in place. Or you can take it off and reinstall it. Not need to purchase a new one.

[@KarenRendell-hs6vg]

Hi there what should pressure gauge show at please? I have black arrow on 2.2 and red between zero and 1 ( sorry woman living alone and I haven’t a clue)

[@plumber-tom9470]

Hmm. Not sure what kind of gauge that would be. System pressures should be higher, from 45 psi to 80 psi.

[@RC.56]

Was adjusting my water pressure at the regulating valve, it was at 50 I use the hose Spicket with a pressure gauge and increased it to 65, then I shut off the main water and drained all the water from the Spicket from the house. Checked the expansion chamber and it has zero psi.

[@plumber-tom9470]

The expansion tank may be defective. If the membrane ruptured then you will still see pressure when the water is on but it will drop to zero when the water is off. In this case you need a new expansion tank. It is important to fill the tank with air pressure when there is no water pressure and the water is off. Otherwise you can get a false reading because there may be less pressure in the air chamber but when the water is on the water pressure will compress the air to the same psi as the water pressure.

[@RC.56]

@@plumber-tom9470 While the water was off and drains and the pressure showing zero, I added air up to 40 psi, turn the water back on, and have not checked it.

[@truth6600]

Tape then dope

[@plumber-tom9470]

I respect that opinion. But the truth is, it works both ways. I put the tape over the dope because it is cleaner, and trust me I have tried it many times both ways. Code does not have any specific requirements about whether tape or dope comes first.

[@larrytheplumber9851]

No code dont its just common sense 😂​@@plumber-tom9470

[@jdsbeau1]

Hi, I just bought and installed an expansion tank because boiler relief valve would spurt water violently and I got hammering sounds. I did not check the levels or adjust the expansion tank - I didn't know it was required, though the factory adjustment would be normal and useful. Not so - when I got the furnace going again, the same thing happened. Is it the expansion tank ? Could I have killed the tank in one shot ? I already replaced the systems water pump and regulator and thermocoupler.

[@plumber-tom9470]

Hmm. That sounds like a tricky one. Noises can be caused by a number of things. But I don't think your new expansion tank is ruined. They usually hold up for years.

[@jdsbeau1]

@@plumber-tom9470 Hi, thanks for getting back to me. I solved the dilemma - I removed the closure large round door in the valve after the expansion tank - it was sludgy and likely stayed close - closing the system, although the valve appeared from the outside to be " open ". One can not always assume the valve is opening and closing. Thanks again.

[@RVail623]

At 1:40 your drawn diagram shows the water inlet at the bottom, which is the correct orientation, AFAIK. Then later in the video, you say that the water inlet should be at the top. Do you have any definitive documentation as to what the "officially recommended" installation method is? Also: teflon tape should be applied first, then the pipe dope.

[@plumber-tom9470]

Hello. Best to check the manufacturer's installation instructions. I really don't think it matters the orientation of the tank. It is not dependent on gravity. Either way, the tank should be supported by something other than the pipe. The order of teflon tape and pipe dope is simply a matter of opinion. I have done it hundreds of times both ways, and I prefer dope first because it is cleaner. Code does not dictate any order, neither do state or local laws so you can do what you prefer.

[@larrytheplumber9851]

​@plumber-tom9470 yea they don't dictate something tht should be common sense son 😂

[@mightyj806]

I have an inlet pressure reducing valve pre set at 12psi. Yet my boiler runs 20 psi cold and almost 25 psi hot. The expansion tank also precharged at 12 psi. My home is only one story (with basement where the boiler is) and the highest piping point is about 8 feet from the boiler. The boiler was installed with the expansion upside down, meaning valve stem points towards ceiling. The circulator was installed right before the return into the boiler. When the maintenance guys come they always say that's ok. I don't believe it. Would adding or reducing pressure from the expansion tank help the problem because there doesn't seem to be any other way to lower the pressure?

[@plumber-tom9470]

You can add pressure to the pressure tank if you want. It is best to have the air pressure in the tank the same as the operating system pressure. But remember that when you pressurize the air in the tank, you will need to either remove the tank from the system, or drain the system to 0 psi, otherwise the pressure in the tank will reflect the current pressure of the fluid in the system. The only way to get an accurate reading on an expansion tank is to have the system pressure at 0 psi.

[@mightyj806]

@@plumber-tom9470 Your response reminded me of another point. When I drain the system just enough to reduce the pressure to 12 it also returns to 20 or higher on it's own. Ok, so it will be easier to remove the tank as it has a cutoff just before it. So you're saying pump it up to 20 and reinstall and that may reduce the operating pressure?

[@plumber-tom9470]

@@mightyj806 If there is a valve near the expansion tank, that is ideal because you can shut it off and not drain the system. Once you have removed the tank, you can adjust the pressure to what it should be in the system.

[@tgamirov]

Air pressure will increase as the diaphragm is pushed back by slightly higher water pressure, so there is some equalizing action.

[@plumber-tom9470]

True statement. Thank you.

[@enricoderojassarson5596]

You should not add air to the tank when the system is hot (pump or water line in service). And there needs to be both air and water in the tank, so you should describe how to determine if the tank is waterlogged.

[@plumber-tom9470]

Good advice and suggestion. Hard to tell if a tank is waterlogged just by looking at it. But as you are probably aware, testing the air valve or removing the tank are the best ways to check whether the tank is waterlogged. I prefer to replace old tanks even if they are not waterlogged.

[@Wolfpack0512]

My system rests at 80psi and will spike as high as 120psi, which it did that on only one sink in the bathroom, does this mean I will need either a reducer or a water pressure regulator?

[@plumber-tom9470]

Yes. If it goes over 80 psi you will need a pressure reducing valve.

[@Wolfpack0512]

Okay thank you! I will buy that now and get a gauge installed in my system too. I appreciate it!

[@plumber-tom9470]

Good plan. Thanks for watching! @@Wolfpack0512

[@ewegot9000]

Why does an expansion tank need a bladder? If I have an air tank with only a single bottom inlet/outlet and connect a water line, the air will remain in the upper portion of the tank and would be compressed by water flowing in to the point at which pressure inside the expansion tank would equal the water line pressure. If additional expansion occurs when the water is heated, the air within the tank will be slightly compressed a bit more just as if there was a bladder inside, no? Obviously the tank would have to remain in an upright position with the single inlet at the bottom so that the air would always remain in the upper portion of the tank. I'm trying to understand why a pressurized bladder is needed inside the expansion tank if there is enough volume within the expansion tank to accommodate both the water line pressure and the additional expansion pressure.

[@plumber-tom9470]

Good question. That theory is correct. That has been tried in the past. However the air pocket inside the tank becomes comprised over time as the air often dissipates into the water. Having a barrier between the water and the air is the only way to ensure that the air will remain and provide the necessary expansion space.

[@ewegot9000]

Okay, so what if I do one of three things, 1) put a thin layer of oil in the DIY tank to avoid air absorption, 2) put a valve in the bottom of the tank into which I can occasionally force more air into the tank, or 3) install a shut off valve before the tank and a drain valve in the bottom to occasionally drain any water from the tank. I know I'm just being cheap but thinking outside the box can sometimes save serious money.

[@5layerinmybelly]

so if waters shooting out of it the diaphragm is broken ??

[@plumber-tom9470]

Yes. Time for a replacement

[@5layerinmybelly]

@@plumber-tom9470 I did 😆 thnaks for the reply

[@plumber-tom9470]

Nice work!@@5layerinmybelly

[@jerrysmith5782]

Important to remember that...if you want to achieve the maximum thermal expansion capacity of your tank...when inflating the air bladder, the tank must have no water pressure applied. Anything that prevents the air bladder from fully expanding to full volume during inflation will reduce the effective capacity of the tank, by limiting the starting volume of air in the tank that is available to be compressed by applied water pressure. To understand this, first visualize an air bladder that, when un-impeded, inflates to completely fill a tank. Then, when equal water pressure is applied, no water at all can enter the tank, yielding a FULL tank of air available to compress due to thermal expansion. Then visualize an air bladder that, when impeded by water pressure, inflates to only partially fill a tank. Then, when equal water pressure is applied, water can partially enter the tank, yielding only a PARTIAL tank of air available to compress due to thermal expansion. There are reasons for deviating from the above, such as, in some cases, you might not need the full capacity of the tank, and then you might be able to extend bladder life by limiting the starting volume of air in the tank...but, in most cases, expansion tanks are inflated with no water pressure applied, so as to achieve the full thermal expansion absorption capacity of the tank.

[@plumber-tom9470]

Well said! Thank you for the explanation!

[@kevinmiller5467]

Why did you put pipe dope then teflon tape in that order? Why not teflon tape then pipe dope?

[@plumber-tom9470]

I prefer to do it that way because it is cleaner. I smear less pipe dope when it is covered with tape. I have done it hundreds of time both ways and I really don’t think one way is more or less likely to leak.

[@kevinmiller5467]

@@plumber-tom9470 Perfect answer, thank you. I'm not a plumber and did it the opposite way.

[@plumber-tom9470]

no problem!@@kevinmiller5467

[@chrissewell1608]

And you didn't explain how to discover your water lines PSI.

[@plumber-tom9470]

Good question. I will have another video on that soon.

[@DontLookBehindYou1]

He did have a pressure gauge in line in the last picture/drawing... So that's one way (not being a smart aleck -most don't have a gauge there)... Some people will test them at the hose bibb if it's after the PRV.