How to Install a Portable Water Expansion Tank

Written by chuck brown
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How to Install a Portable Water Expansion Tank
Potable water expansion tanks can prevent early hot water heater replacement. (water image by the_pix from

Potable water expansion tanks are an ideal solution for absorbing the force of expanding water. By absorbing this excessive force, the expansion tank helps to protect the potable water system from constantly fluctuating water pressure and build-up. Since these are potentially explosive devices, relief valves should also be installed along with the tanks. They must be installed in accordance with local plumbing restrictions and codes. These tanks must not be installed where either the temperature or internal water pressure may exceed the listed tank limitations. This is obviously an installation job for licensed, experienced installers, so proceed with caution.

Skill level:

Things you need

  • Hacksaw
  • T-coupler
  • Torch
  • Solder

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  1. 1

    Examine the tank closely, looking for any signs of damage before beginning the installation. Any tank that appears to be damaged must be returned and not used. Adjust the pre-charge pressure to the same or equal incoming pressure. Replace the plastic air fitting cap and tighten it securely.

  2. 2

    Mount the expansion tank in the cold water side of the water lines coming into the hot water heater. Locate it at some point between the water heater and pressure reducing valve. Turn off the water, drain the line and saw into the line with a hacksaw. Use a T-joint and solder in the joint to the cold water line and mount the tank.

    How to Install a Portable Water Expansion Tank
    Hacksaws make straight copper pipe cuts. (hacksaw image by Aleksandr Ugorenkov from
  3. 3

    Fill the system and check the joints for leaks. Look carefully and thoroughly. Use a dry rag or paper towel and repeatedly wipe the joints, looking for any signs of moisture. Re-solder and repair any leaks.

  4. 4

    Open a hot water fixture and let it run until you do not hear or see any air escaping the line. Let it completely bleed out all the air until you have a solid, steady stream. Shut off the hot water faucet and set the water heater temperature control to the highest temperature setting you want the water to reach. Keep this number as low as you can to save energy on overheating water.

    How to Install a Portable Water Expansion Tank
    Clearing the line of air will prevent it from building up in the tank. (hot tap image by pncphotos from
  5. 5

    Slightly open a hot water faucet to relieve the initial heat expansion. Leave it open until you see that the water heater thermostat is at its normal operating range. When you see that the water heater is within its normal range, shut off the hot water faucet and stop bleeding the system.

Tips and warnings

  • Since water quality can adversely affect the life of the tank, have your water quality tested for corrosive elements such as acidity and chemicals such as chlorine.
  • Do not install a water expansion tank where it will be exposed to temperatures below freezing or above its optimal operating temperature.

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