Water Heater Thermal Expansion Tanks

A thermal expansion tank is designed to help protect potable (drinkable) hot water systems, helping to maintain them and keep them working efficiently. They are used to absorb excess water pressure, which can be caused by thermal expansion as water is heated. With a properly installed tank, the system pressure will be maintained, and will help prevent added stress to various components, saving you headaches - and money - down the road. What is thermal expansion? Find out here.

Water Heater Thermal Expansion Tanks

Arrow expansion tanks
Expansion tanks feature:
  • Protect your plumbing in the event of a pressure increase with these quality thermal expansion tanks
  • Safely controls thermal expansion by accepting the expanded water and keeping the system pressure safely under the relief valve setting
  • Saves water & energy: unlike a pressure relief valve that wastes heated water when activated, these tanks allow the expanded water to be stored in the tank for future use
  • Durable stainless steel (Type 304) connections
  • Food grade reservoir means the tank works great with potable (drinking) water
  • Reduces wear and tear on safety valves, valve stems, and ball seals
  • Maximum operating temperature: 200°F
  • Maximum working pressure: 150 PSI
  • Factory pre-charge: 45 PSI
  • Butyl rubber diaphragm, food grade polypropylene liner
  • Complies with low lead laws - less than .25% weighted average lead content for wettable surface areas
  • Can be installed in any orientation, vertical, horizontal or diagonal
  • Typical residential installation of these thermal exapnsion tanks

Expansion tand diagram

Thermal Expansion Tank Specifications

Ship Wt.
A 101 8 2 12-1/2" 8" 3/4" 5
A 102 18 4.5 15" 11" 3/4" 9
A 103 55 14 19-7/8" 15-1/2" 1" 19
A 104 80 20 27" 15-1/2" 1" 27

Thermal Expansion Tank Quick-Sizing Graph

Water Heater Volume (GAL.)
40 50 60 80 100 120 150 175 200

Color key

Model Description Connection Size Max Gallon
Price & Quantity
A101 Water Heater Thermal Expansion Tank 3/4" connections 2.1 $44.74
A102 Water Heater Thermal Expansion Tank 3/4" connections 4.75 $61.79
A103 Water Heater Thermal Expansion Tank 1" connections 14 $157.47
A104 Water Heater Thermal Expansion Tank 1" connections 20 $222.75

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Frequently Asked Questions

Q. "What is thermal expansion?"
A. When water is heated, it expands in volume by 2 - 3%, depending upon the initial and final temperature. This can mean as much as three or four extra gallons of water in a closed system. If there is no demand for hot water, the expanded volume of water has no place to go. Since water is not compressible, the expanded water cannot be accommodated in the piping system, and therefore it creates hydraulic pressure, exerting a potentially hazardous stress on the system. To learn more about thermal expansion and how you can manage it, click here.

Q. "Why would anyone need an expansion tank?"
A. Water is incompressible. Unlike air, it's impossible to squeeze any quantity of water into a smaller volume. Where that matters is in "closed" water systems such as a water heater with a check valve (pressure regulator and the like) ahead of the heater. When the water gets heated it expands and that extra volume has to go someplace. Without an expansion tank the pressure could rise to a dangerous level in a closed system. A diaphragm type of expansion tank (such as what we sell) is a pressure vessel that contains a flexible membrane totally separating the water from a captive volume of air. Air compresses and as the water temperature rises, creating extra pressure/space, the air in the vessel accommodates that increase. Thereby preventing a potentially dangerous pressure rise.

Q. "What is a closed system?"
A. It is a system that uses a pressure reducing valve when water service pressure is too high for residential applications, usually above 80PSI.

Q. "What size expansion tank should I order for my water heater?"
A. This depends on the size of your water heater and your water pressure. For most small water heaters usually the A101 works. Please refer to this thermal expansion tank quick-sizing chart to find the appropriate thermal expansion tank for your system.

Q. "Your typical installation diagram shows mounting these expansion tanks in a vertical position. Can they be mounted horizontally?"
A. Yes. According to the manufacturer, the A101, A102, A103 and the A104 expansion tanks can be installed horizontal, vertical or even diagonal. Inlet threads up, down or sideways, it doesn't matter. These thermal expansion tanks can be mounted in any orientation and the tank will function correctly.

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