Expansion Tanks

To determine the size needed for your system, use this quick and convenient Expansion Tank Size Calculator.

This category contains Amtrol WELL-X-TROL pre-pressurized well tanks, available in a variety of models and sizes, as well as THERM-X-TROL expansion tanks, designed for use in potable water systems and open loop heating systems.

146 products shown

Sort By:

View By:

  • THERM-X-TROL ST-5 Expansion Tank View Specs
    • SKU: 140N43
    • Brand: Amtrol

    $43.49 / each

    $165.96 / box
    4 x $41.49

    In Stock! (25 Available) Ships in 24-48 Hrs
  • THERM-X-TROL ST-12 Expansion Tank View Specs
    • SKU: 141N43
    • Brand: Amtrol

    $57.95 / each

    $221.96 / box
    4 x $55.49

    In Stock! (40 Available) Ships in 24-48 Hrs
  • THERM-X-TROL ST-8 Expansion Tank View Specs
    • SKU: 140N738
    • Brand: Amtrol

    $55.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-25V Expansion Tank (10.3 Gallon Volume) View Specs

    $118.95 / each

    $344.85 / box
    3 x $114.95

    Out of Stock Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-30V Expansion Tank (14 Gallon Volume) View Specs

    $169.85 / each

    In Stock! (3 Available) Ships in 24-48 Hrs
  • THERM-X-TROL ST-42V Expansion Tank (20 Gallon Volume) View Specs

    $235.85 / each

    In Stock! (1 Available) Ships in 24-48 Hrs
  • THERM-X-TROL ST-60V-C ASME Expansion Tank (25 Gallon Volume) View Specs

    $1,999.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-60V Expansion Tank (34 Gallon Volume) View Specs

    $274.85 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-20V-C ASME Expansion Tank (8 Gallon Volume) View Specs

    $1,625.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-80V Expansion Tank (44 Gallon Volume) View Specs

    $325.85 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-180V Expansion Tank (62 Gallon Volume) View Specs

    $489.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-210V Expansion Tank (86 Gallon Volume) View Specs

    $529.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-SPAN T-5 Expansion Tank (2 Gallon Volume) View Specs
    • SKU: 140735
    • Brand: Amtrol

    $33.95 / each

    $130.36 / box
    4 x $32.59

    In Stock! (23 Available) Ships in 24-48 Hrs
  • THERM-X-SPAN T-12 Expansion Tank (4.4 Gallon Volume) View Specs

    $42.95 / each

    $165.00 / box
    4 x $41.25

    In Stock! (11 Available) Ships in 24-48 Hrs
  • THERM-X-TROL ASME ST-12-C Expansion Tank View Specs
    • SKU: 141-326
    • Brand: Amtrol

    $1,399.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-200V Expansion Tank (81 Gallon Volume) View Specs

    $629.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ST-454-C, Replaceable Bladder Design ASME Tank (317 Gallon, 150 PSI) View Specs

    $11,419.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • THERM-X-TROL ASME ST-30V-C Expansion Tank View Specs
    • SKU: 143-327
    • Brand: Amtrol

    $1,499.95 / each

    Non-Stock Item Allow 1-2 Weeks to Ship Out
  • WX-101 (140PR1), 2 Gal WELL-X-TROL In-Line Well Tank View Specs

    $53.95 / each

    $209.40 / box
    4 x $52.35

    Out of Stock Allow 1-2 Weeks to Ship Out
  • WX-102 (141PR1), 4.4 Gal WELL-X-TROL In-Line Well Tank View Specs

    $73.95 / each

    $287.00 / box
    4 x $71.75

    In Stock! (1 Available) Ships in 24-48 Hrs

More About Expansion Tanks

An expansion tank is designed to relieve pressure in both a potable water and closed heating system. An expansion tank ensures a constant pressure is maintained within the pipes so they do not get damaged from excess pressure.

An expansion tank has two parts which are divided by a rubber diaphragm. The top portion of the tank is connected to the hot water system and is filled with water. The bottom portion is filled with air set at approximately 12 psi. As the hot water system is turned on or off, pressure increases. As pressure increases, the diaphragm in the expansion tank is pushed down. This compresses the air in the tank, creating more space for excess water to enter. This relieves excess pressure in the system and prevents pipes in the system from being damaged.

In the event that the diaphragm fails, the tank will completely fill with water. If this occurs, the tank must be replaced immediately. To check if the expansion tank is working properly, simply place your hand on the tank and feel its temperature. The top portion of the tank should feel warm to the touch, and the bottom portion of the tank should be room temperature. If the entire tank is warm, it is likely that the tank has completely filled with hot water.

Expansion tanks have capacities ranging from 2 gallons to several hundred gallons. To determine the size needed for your system, use the Expansion Tank Size Calculator located here.

We offer a wide selection of
Therm-X-Trol and Well-X-Trol expansion tanks to suit all of your plumbing and heating needs.