--- product_id: 8847368 title: "ST-12 Thermal Expansion Tank" brand: "amtrol" price: "β‚±20737" currency: PHP in_stock: true reviews_count: 7 category: "Amtrol" url: https://www.desertcart.ph/products/8847368-st-12-thermal-expansion-tank store_origin: PH region: Philippines --- # 4.4 Gallon capacity Protects plumbing & heater longevity Prevents pressure relief valve trips ST-12 Thermal Expansion Tank **Brand:** amtrol **Price:** β‚±20737 **Availability:** βœ… In Stock ## Summary > πŸ’‘ Upgrade your home’s water system with smart pressure control! ## Quick Answers - **What is this?** ST-12 Thermal Expansion Tank by amtrol - **How much does it cost?** β‚±20737 with free shipping - **Is it available?** Yes, in stock and ready to ship - **Where can I buy it?** [www.desertcart.ph](https://www.desertcart.ph/products/8847368-st-12-thermal-expansion-tank) ## Best For - amtrol enthusiasts ## Why This Product - Trusted amtrol brand quality - Free international shipping included - Worldwide delivery with tracking - 15-day hassle-free returns ## Key Features - β€’ **Safety First:** Prevents dangerous pressure build-up, ensuring peace of mind at home - β€’ **Durability Boost:** Extends water heater and plumbing fixture lifespan by preventing premature failure - β€’ **Easy Maintenance:** Visual bladder health indicator and factory pre-charged for hassle-free installation - β€’ **Pressure Guardian:** Keeps system pressure below relief valve threshold to avoid leaks and damage - β€’ **Energy & Water Saver:** Eliminates costly thermal expansion waste for smarter utility bills ## Overview The Amtrol ST-12 Thermal Expansion Tank (4.4 gallons) is engineered to manage thermal expansion in closed potable water systems, preventing pressure build-up that wastes energy, water, and shortens equipment life. It safeguards your water heater and plumbing by maintaining pressure below relief valve settings, enhancing safety and efficiency. Factory pre-charged and designed for easy installation, it’s a trusted, durable solution favored by professionals and homeowners alike. ## Description Amtrol ST-12 THERM-X-TROL Expansion Tank, 4.4 Gallon (141N43) What Is Thermal Expansion? With modern plumbing codes mandating backflow prevention, thermal expansion can cause pressure buildup in domestic water systems. When demand is put upon a potable water system, hot water is drawn from the water heater. Cold water from the supply line enters the water heater to replenish it. The colder water is heated to replace the hot water used. With the installation of a backflow preventer, check valve or pressure reducing valve on the supply line, the water heater and the system piping form a closed plumbing system under pressure. As the water is heated, thermal expansion occurs. Pressure increases until the relief valve opens and the expanded water "spills" from the water heater. This "spillage" results in wasted BTU's and a potential safety hazard for the homeowner. Closed Potable Hot Water system without THERM-X-TROL Backflow preventer, pressure reducing valve or meter causes expanded (heated) water to build pressure causing the relief valve to open resulting in: Wasted BTU's Shortened water heater life Wasted municipal water and sewer dollars Potential safety hazard for homeowner The Amtrol THERM-X-TROL ST-12 Expansion Tank is designed to eliminate this problem by providing control of maximum pressures at a level below the relief valve setting. It also provides an additional space in the system to accommodate the increased volume of water created by thermal expansion, returning it to the system when hot water delivery is demanded. Review: Great value-quality product-Fast Shipping!!! - Seller NY Direct shipped fast and item arrived in two days safe and sound. New ST-12 replaced a 24 yr old ST-8 that went bad. From what I researched this brand and series is the best, made in USA and really was not much more than other brands. desertcart and NY Direct had best price anywhere after a long search. I went with the larger 4.4 gallon ST-12 vs the 2.0 gallon ST-8 it replaced. I read its ok and maybe even better to go a size up but not to go below what you have or water heater rated for. Maybe overkill but it was $12 more than the ST-8 and I had the space. Installation went well. Manual states manufacturer recommends installation with threaded pipe side up in a hanging position. Reviews all over are mixed but it seems like its the best way to mount it to get the longest most effective use out of it before needing a new one. I chose not to follow directions and just replaced it with the current configuration set up in my house with thread side down. Some reviews said they talked to manufacturer direct and wrong way, not the recommended way is fine and it will work, just may not last as long. It has to do with the rubber bladder inside and installed the recommended way keeps all the rubber wet all the time and can prolong item life span in theory. Some reviews said they had difficulty getting it to mount with the small optional plastic tubulator piece inside but I did not have any issue. I just made sure to give it an extra push till it seated inside with the end if a metal flashlight and pressing with my thumbs alone would not move it enough to seat all the way. With my digital air pressure reader it came with a charge from the factory of 51.8 pounds of air. I purchases a $10 pressure reader of desertcart and it showed my house supply lines at 48-50 pounds. I felt that was close enough so let it stay at the 51.8 factory charge and not mess with it. Make sure to screw the cap back on tight by hand as these now have a clear plastic cap that changes colors if the bladder goes bad and it leaks. Not sure what all the drama is about in reviews removing the old one full if water when installed not the recommended way. Yes it will leak water but I just wrapped a bath towel loosely around under the tank and use a pipe wrench to loosen and pair of channel locks to secure the pipe the tank connects to. Then I just spun the tank. When it gets loose just tip it over quickly and I barely lost any water. Carry over to laundry tub and tilt it on an angle and let the water drain out. Some of it stays stuck in the bladder and you cannot get it out. Probably varies for each failure where it went bad. Teflon tape to the nee tank threads. Spin by hand then use wrenches to tighten. Turn water supply back on slow so you do not slam the tank or your system. There are directions on keeping a nearby faucet open till you bring your water heater back up to full heat. You wait till your water heater burner is done burning and reached the temp you desire so full heat expansion is reached in the water lines and tank and then you can shut the nearby faucet off. Slowly open all your faucets to purge any air and then just revisit the tank a few times to check for leaks. Usually when I mess with plumbing something goes wrong or I have to deal with leaks but this was a simple and quick install with no issues. I am very cheap but felt the extra $10-40 cost over the cheapest made overseas by the lowest bidder model was not worth the savings. I plan on living in the house a long time and now I know how to check visually and with a pressure gauge if its working properly every 6-12 months. I did notice prior to install I was clearing out the aerators on all my faucets and there were little pieces if black rubber which looked the exact same as the rubber particles coming out of the tank from the rotted bladder of the bad tank when I drained it. So, it warrants at least annual inspection as recommended to make sure the bladder is working, at the correct pressure to match up with incoming supply line pressure. Cleaning out allfaucets aerators annually seems to be a good idea too. You can buy a aerator removal tool kit for under $10 at any big box store. It comes with four tools of the most common sizes. It would also seem ideal to clean the aerators once again after you change the tank out to get the old black rubber particle stuff out of your aerators or periodically replace them. I read you can drop them in regular household white vinegar to soak clean them just like you can with shower heads to clean the buildup gunk off. Review: Good product works as it should - Worked as it should installed ## Features - Eliminates the waste of energy and water, thus saving money - Prevents the relief valve from going off - Protects the water heater and plumbing fixtures from premauture failure - Prevents a dangerous pressure build-up in the system ## Technical Specifications | Specification | Value | |---------------|-------| | ASIN | B001BNPSFW | | Batteries Included? | No | | Batteries Required? | No | | Best Sellers Rank | #99,318 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #173 in Water Heater Replacement Parts | | Color | White | | Customer Reviews | 4.6 4.6 out of 5 stars (313) | | Date First Available | June 25, 2008 | | Is Discontinued By Manufacturer | No | | Item Package Quantity | 1 | | Item Weight | 2.2 pounds | | Item model number | ST-12 | | Manufacturer | AMTROL | | National Stock Number | 5430-01-626-6547 | | Part Number | ST-12 | | Power Source | Ac/dc | | Product Dimensions | 8 x 11 x 15 inches | | Size | one-size | ## Images ![ST-12 Thermal Expansion Tank - Image 1](https://m.media-amazon.com/images/I/51Uq0ljbAXL.jpg) ## Questions & Answers **Q: Is this for potable water?** A: It is not made for potable water system. But in a regular installation some water from the tank can mix with a potable water. The tank has a polypropylene liner and butyl diaphragm, which may be in contact with water. You have to decide for yourself if you want to drink water from a polypropylene container. **Q: Can this tank be install horizontally?** A: Amtrol instruction says: "Mount tank vertically in downward position only. Ensure the piping can support the entire weight of the tank when full of water". This makes sense to me. **Q: Is this compatable with ethylene glycol? I want it for the glycol side of a heat exchanger on a solar water heater.** A: I don't know. It may be best to contact the Amtrol technical support to see if ethylene glycol is compatible with the bladder diaphragm chemistry in this unit. **Q: what's the capacity in gallons?** A: It's a 12 liter tank, so it holds approximately 4.4 gallons. ## Customer Reviews ### ⭐⭐⭐⭐⭐ Great value-quality product-Fast Shipping!!! *by A***S on March 16, 2023* Seller NY Direct shipped fast and item arrived in two days safe and sound. New ST-12 replaced a 24 yr old ST-8 that went bad. From what I researched this brand and series is the best, made in USA and really was not much more than other brands. Amazon and NY Direct had best price anywhere after a long search. I went with the larger 4.4 gallon ST-12 vs the 2.0 gallon ST-8 it replaced. I read its ok and maybe even better to go a size up but not to go below what you have or water heater rated for. Maybe overkill but it was $12 more than the ST-8 and I had the space. Installation went well. Manual states manufacturer recommends installation with threaded pipe side up in a hanging position. Reviews all over are mixed but it seems like its the best way to mount it to get the longest most effective use out of it before needing a new one. I chose not to follow directions and just replaced it with the current configuration set up in my house with thread side down. Some reviews said they talked to manufacturer direct and wrong way, not the recommended way is fine and it will work, just may not last as long. It has to do with the rubber bladder inside and installed the recommended way keeps all the rubber wet all the time and can prolong item life span in theory. Some reviews said they had difficulty getting it to mount with the small optional plastic tubulator piece inside but I did not have any issue. I just made sure to give it an extra push till it seated inside with the end if a metal flashlight and pressing with my thumbs alone would not move it enough to seat all the way. With my digital air pressure reader it came with a charge from the factory of 51.8 pounds of air. I purchases a $10 pressure reader of Amazon and it showed my house supply lines at 48-50 pounds. I felt that was close enough so let it stay at the 51.8 factory charge and not mess with it. Make sure to screw the cap back on tight by hand as these now have a clear plastic cap that changes colors if the bladder goes bad and it leaks. Not sure what all the drama is about in reviews removing the old one full if water when installed not the recommended way. Yes it will leak water but I just wrapped a bath towel loosely around under the tank and use a pipe wrench to loosen and pair of channel locks to secure the pipe the tank connects to. Then I just spun the tank. When it gets loose just tip it over quickly and I barely lost any water. Carry over to laundry tub and tilt it on an angle and let the water drain out. Some of it stays stuck in the bladder and you cannot get it out. Probably varies for each failure where it went bad. Teflon tape to the nee tank threads. Spin by hand then use wrenches to tighten. Turn water supply back on slow so you do not slam the tank or your system. There are directions on keeping a nearby faucet open till you bring your water heater back up to full heat. You wait till your water heater burner is done burning and reached the temp you desire so full heat expansion is reached in the water lines and tank and then you can shut the nearby faucet off. Slowly open all your faucets to purge any air and then just revisit the tank a few times to check for leaks. Usually when I mess with plumbing something goes wrong or I have to deal with leaks but this was a simple and quick install with no issues. I am very cheap but felt the extra $10-40 cost over the cheapest made overseas by the lowest bidder model was not worth the savings. I plan on living in the house a long time and now I know how to check visually and with a pressure gauge if its working properly every 6-12 months. I did notice prior to install I was clearing out the aerators on all my faucets and there were little pieces if black rubber which looked the exact same as the rubber particles coming out of the tank from the rotted bladder of the bad tank when I drained it. So, it warrants at least annual inspection as recommended to make sure the bladder is working, at the correct pressure to match up with incoming supply line pressure. Cleaning out allfaucets aerators annually seems to be a good idea too. You can buy a aerator removal tool kit for under $10 at any big box store. It comes with four tools of the most common sizes. It would also seem ideal to clean the aerators once again after you change the tank out to get the old black rubber particle stuff out of your aerators or periodically replace them. I read you can drop them in regular household white vinegar to soak clean them just like you can with shower heads to clean the buildup gunk off. ### ⭐⭐⭐⭐⭐ Good product works as it should *by J***Y on January 9, 2026* Worked as it should installed ### ⭐⭐⭐⭐⭐ Very happy *by A***R on September 7, 2025* We needed to replace ours and this came when expected and was an easy install, extends the life of my water heater ## Frequently Bought Together - Amtrol ST-12 Thermal Expansion Tank - HoldRite QuickStrap Universal Expansion Tank Water Heater Wall Mounting Bracket, Stainless Steel, QS-U - MEASUREMAN 0-200 PSI Water Pressure Gauge, 2-1/2'' Dial, Hose bib Pressure Gauge, Home Water Pressure Tester, Durable 3/4” Hose Thread, Water Pressure Gauge for Home --- ## Why Shop on Desertcart? - πŸ›’ **Trusted by 1.3+ Million Shoppers** β€” Serving international shoppers since 2016 - 🌍 **Shop Globally** β€” Access 737+ million products across 21 categories - πŸ’° **No Hidden Fees** β€” All customs, duties, and taxes included in the price - πŸ”„ **15-Day Free Returns** β€” Hassle-free returns (30 days for PRO members) - πŸ”’ **Secure Payments** β€” Trusted payment options with buyer protection - ⭐ **TrustPilot Rated 4.5/5** β€” Based on 8,000+ happy customer reviews **Shop now:** [https://www.desertcart.ph/products/8847368-st-12-thermal-expansion-tank](https://www.desertcart.ph/products/8847368-st-12-thermal-expansion-tank) --- *Product available on Desertcart Philippines* *Store origin: PH* *Last updated: 2026-05-03*