Model # 141N43

Internet #204296372

Amtrol Therm-X-Trol ST-12 Expansion Tank


Therm-X-Trol ST-12 Expansion Tank

$6715 /each
store icon Loading Buying Options...
package icon Loading Buying Options...
Sorry, but we ran into issues loading these options. Please try refreshing.

Frequently Bought Together

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

Info & Guides

You will need Adobe® Acrobat® Reader to view PDF documents.  Download a free copy from the Adobe Web site.

Compare Similar

$40.18 /each
$41.85 /each
$67.15 /each
Name 4.5 gal. Thermal Expansion Tank 2 gal. Air Expansion Tank Therm-X-Trol ST-12 Expansion Tank
Brand Eastman Amtrol Amtrol
Ratings (2) (0) (21)
Product Width (in.) 11 7.5 9
Product Height (in.) 15 12.75 15
View Product View Product View Product




More Products With These Features


Customer Questions & Answers

is this st-12 expansion tank always filled with water, and how would you know if it is bad?

Asked by: Dewey
The rubber diaphragm in the tank separates the air and the water. Excessive water pressure compresses the air. When the line pressure drops the air forces water back into the system. To answer your question, if you get water out when you check the air pressure at the Schrader (air) valve, the diaphragm has failed and the tank needs to be replaced.
Answered by: scotner
Date published: 2017-07-14

does it matter if this is installed with the air cap on the top and the screw in fitting on the bottom?

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.
Asked by: diyguy
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.
Answered by: lawdog
Date published: 2016-04-01

Sizing correctly

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?
Asked by: Curt
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.
Answered by: BawDawg
Date published: 2017-06-03

if i tap on my expansion tank it sounds like it is full of concrete. does this mean its bad

Asked by: eric
yes ... the bladder inside is torn and water has filled the cavity where air should be
Answered by: jace
Date published: 2016-09-21
  • y_2017, m_7, d_19, h_10CST
  • bvseo_bulk, prod_bvqa, vn_bulk_1.0.0-hotfix-1
  • cp_1, bvpage1
  • co_hasquestionsanswers, tq_17
  • loc_, sid_204296372, prod, sort_[SortEntry(order=NUM_ANSWERS, direction=DESCENDING), SortEntry(order=SUBMISSION_TIME, direction=DESCENDING), SortEntry(order=LAST_APPROVED_ANSWER_SUBMISSION_TIME, direction=DESCENDING), SortEntry(order=LAST_APPROVED_ANSWER_SUBMISSION_TIME, direction=DESCENDING), SortEntry(order=BEST_ANSWER_FEEDBACK_COUNT, direction=DESCENDING), SortEntry(order=POSITIVE_ANSWER_FEEDBACK_COUNT, direction=DESCENDING), SortEntry(order=NUM_ANSWERS, direction=DESCENDING)]
  • clientName_homedepot
  • bvseo_sdk, java_sdk, bvseo-3.1.1
  • CLOUD, getContent, 31ms

Customer Reviews

Therm-X-Trol ST-12 Expansion Tank is rated 4.7 out of 5 by 21.
Rated 5 out of 5 by from I replaced my old Amtrol expansion tank after 17years. I bought the same model Amtrol and had no... I replaced my old Amtrol expansion tank after 17years. I bought the same model Amtrol and had no problems installing it. It was very easy. I hope this one last as long as my other one did. I also replaced the hot water heater so that everything works well together. Very Happy.
Date published: 2017-02-22
Rated 4 out of 5 by from 4 Star Review Rating provided by a verified purchaser
Date published: 2017-04-04
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
  • y_2017, m_7, d_18, h_22
  • bvseo_bulk, prod_bvrr, vn_bulk_1.0.0-hotfix-1
  • cp_1, bvpage1
  • co_hasreviews, tv_0, tr_21
  • loc_, sid_204296372, prod, sort_[SortEntry(order=RELEVANCE, direction=DESCENDING)]
  • clientName_homedepot
  • bvseo_sdk, java_sdk, bvseo-3.1.1
  • CLOUD, getContent, 31ms