Model # 141N43

Internet #204296372

Amtrol Therm-X-Trol ST-12 Expansion Tank
0642031395672

Amtrol

Therm-X-Trol ST-12 Expansion Tank

$64.57 /each

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Product Overview

AMTROL ST-12 (Therm-X-Trol) is a water heater expansion tank, designed for use in domestic hot water heating systems to eliminate the potential hazards of water expansion. Water heater expansion tank is commonly installed in a domestic hot water system that contains a backflow preventer, a check valve or a pressure reducing valve. AMTROL ST-12 Applications: Residential water heaters, Laundromats, dormitories, office/apartment buildings, restaurants, etc.

  • Eliminates the waste of energy and water, thus saving money
  • Protects the water heater and plumbing fixtures from premature failure
  • Prevents a dangerous pressure build-up in the system
  • Prevents the relief valve from going off
  • Therm-X-Trol brand is the #1 choice of professional installers
  • A professional plumber should check the complete system, including the Therm-X-Trol, yearly and more frequently as the system ages
  • Click here to check out our buying guide on water heaters

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Customer Questions & Answers

15 Questions22 Answers

Customer Questions & Answers

Therm-X-Trol ST-12 Expansion Tank
Therm-X-Trol ST-12 Expansion Tank

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This question is from Therm-X-Trol ST-12 Expansion Tank
 
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does it matter if this is installed with the air cap on the top and the screw in fitting on the bottom?

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February 16, 2015
I have one of these that was installed 18 years ago with the air cap on the top and the cold water supply fitting on the bottom. (opposite of the product photo). Im just curious if it matters which orientation it goes.
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Asked by
castle rock colorado
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March 14, 2016
Answer: 
Yes, it can matter. The idea of the tank is that expanded hot water in the system will cause water to push against the bladder for expansion, and the bladder will push it back, and thus the water will expand into the tank, and back out depending upon the water pressure, This in part aids in keeping the system operating at a stable pressure. If your bladder wears out and leaks, the tank will fill with Read More
Yes, it can matter. The idea of the tank is that expanded hot water in the system will cause water to push against the bladder for expansion, and the bladder will push it back, and thus the water will expand into the tank, and back out depending upon the water pressure, This in part aids in keeping the system operating at a stable pressure. If your bladder wears out and leaks, the tank will fill with water. If the tank is suspended with the air valve on the bottom, you will notice water flow out the air valve when you test it, and a tank hanging down from its fitting is probably a lot more stable when full of water than it would be if it were inverted. Some will argue that solids in the water may fall into the tank when it hangs down, and will not collect on the bladder when it is hanging with the air valve at the top. These solids have been argued to degrade a bladder. The st-12 comes with a device that is intended to prevent these solids from accumulating on the bladder. Read Less
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Asked by
pa.
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October 6, 2015
Answer: 
does not matter !!!
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February 20, 2015
Answer: 
The orientation of the unit is not relevant to its operation.
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This question is from Therm-X-Trol ST-12 Expansion Tank
 
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is this st-12 expansion tank always filled with water, and how would you know if it is bad?

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Long Island, N Y
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September 26, 2014
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Asked by
Missouri
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February 4, 2015
Answer: 
I don't know if it is always filled with water or not. The pressure relief valve on my hot water heater was letting water flow out. A plumber friend suggested that it might be the expansion tank tied to the system. Seems the bladder in the tank will rupture after a while, in my case 16 years. Replaced the tank with same brand and model as originally installed, problem fixed.
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December 11, 2014
Answer: 
Should be if it's doing its job properly. The only way I knew mine was bad was it started leaking down the outside of it.
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Asked by
Colorado
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September 30, 2014
Answer: 
The rubber bladder does not contain water only air, which you preset to your domestic water pressure. The water surrounds the bladder and if it is bad you get what sounds like spurts of water or air out of a faucet. That's what mine was doing and after I put the new one on it quit that spurting.
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This question is from Therm-X-Trol ST-12 Expansion Tank
 
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Sizing correctly

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Asked by
Pittsburgh PA
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September 15, 2015
The incoming house pressure is 120 PSI. I will reduce to 60 PSI with a regulator. I'll be installing a brand new natural gas 40 gallon hot water heater. Would a 2 gallon expansion tank be sufficient or will I need to move to the 5 gallon unit?
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Asked by
Seattle
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Home Improvement Profile: DIYer
September 30, 2015
Answer: 
ST-5 at 140 degrees avg
ST-8 at 160
Generally, I would go with the larger model as the expense is negligible. Amtrol has a sizing guide on their website.
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Asked by
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September 17, 2015
Answer: 
Great question. I think you will be fine with the smaller but I will put a link to the on line calculator below. Please keep in mind that the biggest error with thermal expansion tanks is that contractors think they are plug and play. You need to balance the tank to the house pressure during install. This may me mean adding or removing pressure from the side of the tank that has the gas. This is done by Read More
Great question. I think you will be fine with the smaller but I will put a link to the on line calculator below. Please keep in mind that the biggest error with thermal expansion tanks is that contractors think they are plug and play. You need to balance the tank to the house pressure during install. This may me mean adding or removing pressure from the side of the tank that has the gas. This is done by letting some of the nitrogen out at the schrader valve or pumping air in with a bicycle pump. Also keep in mind that pressure reducing valves have a limited life. Eventually water will leak by the stops and pressurize the down stream system. It will still work well when water is flowing but you will find that pressure builds when it is not. When this happens and the relief valve starts to burp periodically, don't assume the thermal tank is bad, it is more likely the reducing valve. For this reason it is always good to install a pressure gauge on the down stream sized. Install it with a ball valve protecting it. This will allow you to take pressure reading and then shut off the pressure to the gauge. http://www.amtrol.com/support/therm_res_sizing.html Read Less
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if i tap on my expansion tank it sounds like it is full of concrete. does this mean its bad

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new york
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March 4, 2015
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Asked by
pa.
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October 6, 2015
Answer: 
yes ... the bladder inside is torn and water has filled the cavity where air should be
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Asked by
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March 17, 2015
Answer: 
Thermal expansion tanks need to be calibrated when installed but many contractors forget or don't know they need to do this. So it could be completely filled with water because it is bad or was not set up properly. I would start by pushing on the schrader valve, AKA the bike tire air valve looking thing at the bottom. If water comes out you know the diaphragm has ripped and the unit is dead. If air comes Read More
Thermal expansion tanks need to be calibrated when installed but many contractors forget or don't know they need to do this. So it could be completely filled with water because it is bad or was not set up properly. I would start by pushing on the schrader valve, AKA the bike tire air valve looking thing at the bottom. If water comes out you know the diaphragm has ripped and the unit is dead. If air comes out you know it is still good. Then you need to check the pressure and calibrate it to the water pressure in your house, by letting air in or out. Directions are on the Amtrol web site. Please note this is a expansion tank for a hot water heater, expansion tanks for boilers or forced hot water heating systems are different. If you have further questions please feel free to call
chris 1 800 445 5816
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Customer Reviews

Therm-X-Trol ST-12 Expansion Tank is rated 4.7 out of 5 by 19.
Rated 5 out of 5 by from Meets My Requirements Was shipped quickly. Was the expansion tank I expected. Easy pickup at store with no shipping costs. A good deal for me all the way round. There really isn't anything else I can say about this purchase. Service at pickup counter was fast and polite. As this is the second time my review has been rejected I must add that I think the review length requirement verges on being stupid! George
Date published: 2016-09-21
Rated 5 out of 5 by from Product was delivered quickly and is a perfect fit for my water heater. Product was delivered quickly and is a perfect fit for my water heater.
Date published: 2016-12-29
Rated 5 out of 5 by from Easy install and directions are great! The thermal expansion tank was very easy to install as were the directions to follow. The thermal expansion tank was a replacement for a unit which was worn out. The tank was a near identical replacement for the exixting unit. I would highly recommend this product if you have a hot water heater that has a back flow preventor installed somewhere in line to allow the water to expand. Othewise you may create a situtation where the pipes may burst due to over pressure.
Date published: 2013-12-10
Rated 4 out of 5 by from Larger Tank Required for many installations Any time the house water pressure exceeds 60 psi, and many do, mine was 80 psi past the water softener system, the plumber should install a 5 gallon expansion tank, not a 2 gallon! Most plumbers do no measuring of system pressure, slap a 2 gallon tank up, and do not match the air pressure in tank to system pressure. I am now set at 65 psi after installing gauge and pressure reducing valve and THAT IS BOTH TANK AND SYSTEM PRESSURE! Wonder why your pre-charged 2 gallon tank with only 30 psi from the factory fails after 2 to 3 years? Tank and system pressure have not be matched. PLUMBERS NEED TO GO TO SCHOOL ON THIS ONE!! Hot water tank mfg'rs specify that exceeding 60 psi and above get 5 gallon expansion tank, not 2 gallon. Larger rubber badder can withstand higher air pressure in 60 psi plus systems.
Date published: 2014-02-25
Rated 5 out of 5 by from Works as advertised After installing a solar hot water system that utilizes a 120 gallon tank, I started having elevated water pressure (at times) in the house. I was also getting pipe "hammering," and was afraid I'd end up with a broken pipe. My previous hot water heater was a 50 gallon unit which must have had the same issues, but to a much lesser extent. I never noticed the problem until the larger tank was installed. The Amtrol thermal expansion tank seems to have solved the problems. It's been in for about two weeks now, and haven't had a single high pressure episode, or any pipe hammering since. The unit appears to be of very high quality, and I had no problems installing it...very simple. I ended up making my own mounting bracket for the unit. There are commercially available brackets made, but the Home Depot did not carry them, or offer them on their website. To save the cost + shipping from the other suppliers, I built a simple unit out of plywood, and a couple of large hose clamps.
Date published: 2014-01-11
Rated 5 out of 5 by from Does What it is supposed to! City installed new water meters with a check valve in the system. Old system did not have check valve. Since the new water meter was put in my water heater started to relieve thermal caused pressure through the safety valve. Always water in the bucket as our basement has no drains. Our city water pressure was 70 PSI. Matched the tank pressure to this, installed the tank, and the water heater safety valve has not released any water due to pressure. Good value and easy to install.
Date published: 2014-04-18
Rated 3 out of 5 by from Arrived Damaned in original sealed box. Came wonderfully packaged from homedepot.com. Too bad who ever put it in it's original box had dropped it on it's threads. Do not have the time to send it back, I will have to spend a bunch of time with a small file to clean up the damaged threads so it will even screw in. Looks like a nice tank and all, just very VERY annoyed that new out of the box, the threads are damaged to the point it will not even attempt to screw in.
Date published: 2014-04-17
Rated 5 out of 5 by from Therm-x-trol Easy to install ... decent price ... exact fit as my old one . Good Product
Date published: 2015-10-06
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