--- product_id: 8847368 title: "Amtrol ST-12 Thermal Expansion Tank" brand: "amtrol" price: "NZ$132" currency: NZD in_stock: false url: https://www.desertcart.nz/products/8847368-amtrol-st-12-thermal-expansion-tank store_origin: NZ region: New Zealand --- # 4.4 Gallon capacity Protects plumbing & heater longevity Prevents pressure relief valve trips Amtrol ST-12 Thermal Expansion Tank **Brand:** amtrol **Price:** NZ$132 **Availability:** ❌ Out of Stock ## Summary > πŸ’§ Stay ahead of pressure spikesβ€”protect your home and wallet with Amtrol ST-12! ## Quick Answers - **What is this?** Amtrol ST-12 Thermal Expansion Tank by amtrol - **How much does it cost?** NZ$132 with free shipping - **Is it available?** Currently out of stock - **Where can I buy it?** [www.desertcart.nz](https://www.desertcart.nz/products/8847368-amtrol-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€’ **Trusted Quality:** Made in USA with a proven track record and 4.6-star rating from 300+ users - β€’ **Durability Boost:** Extends water heater and plumbing lifespan by preventing premature failures - 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 - β€’ **Easy Installation & Maintenance:** Designed for hassle-free mounting and simple pressure checks with visual indicator ## Overview The Amtrol ST-12 Thermal Expansion Tank is a 4.4-gallon solution engineered to manage thermal expansion in closed potable water systems. By absorbing excess pressure, it prevents relief valve discharge, conserves water and energy, and safeguards your water heater and plumbing from premature wear. Trusted by professionals and homeowners alike, this durable, easy-to-install tank ensures efficient, safe hot water delivery while reducing costly system failures. ## 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. ## 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 | | Best Sellers Rank | #428,499 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #1,029 in Water Heater Replacement Parts | | Color | White | | Customer Reviews | 4.6 4.6 out of 5 stars (324) | | Date First Available | June 25, 2008 | | 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 ![Amtrol ST-12 Thermal Expansion Tank - Image 1](https://m.media-amazon.com/images/I/51XD57YOGDL.jpg) ![Amtrol ST-12 Thermal Expansion Tank - Image 2](https://m.media-amazon.com/images/I/312KaeZK5cL.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. ## 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.nz/products/8847368-amtrol-st-12-thermal-expansion-tank](https://www.desertcart.nz/products/8847368-amtrol-st-12-thermal-expansion-tank) --- *Product available on Desertcart New Zealand* *Store origin: NZ* *Last updated: 2026-10-01*