Home How to size and select a proper Expansion Tank

How to size and select a proper Expansion Tank

 

Overview

 

When water is heated, it expands and its volume increases. Since water is considered non-compressible, in a closed-loop system, this thermal expansion puts an incredible amount of pressure on the piping and components of the entire system. If unresolved, this water pressure could cause leaks and even complete ruptures in the piping. Expansion tanks provide extra space for the expanded water and relieve the system’s pressure. Other than that, not having an expansion tank will allow the pressure to open your relief valve resulting in wasted energy, shortened system life, and an overall potential safety hazard.

The expansion tank itself is just a container of air separated from water by a diaphragm.

When the heating system is filled with cold water, the expansion tank’s pre-charge pressure is equal to its fill pressure which causes the expansion tank’s diaphragm to extend fully against the tank. As the water temperature of the system increases, the expanded water is absorbed by the expansion tank. After the water temperature has reached its maximum and begins to decrease, the diaphragm returns the cooled water back to the system.

 

Types of Expansion Tanks

 

There are several types of expansion tanks available depending on your system’s needs. Domestic hot water plumbing systems use Amtrol’s Therm-X-Trol expansion tanks. For radiant and hydronic heating systems, Amtrol’s Extrol, Radiant Extrol, or a Fill-Trol expansion tank should be used.

 

Choosing the right size for your Expansion Tank

 

Before purchasing an expansion tank, you should find out how large of an expansion tank your system will require. The decision will be based on two factors. The first is your hot water heater’s or boiler’s capacity in gallons. This information will be on your water heater’s or boiler’s factory label. The second is the water pressure in your piping system. For plumbing applications, this information can be acquired by either attaching a small gauge to any faucet or by calling your local water supply company. For hydronic and radiant heating applications, the system’s pressure usually never exceeds 30 psi.

If the expansion tank you purchase is smaller than what your system requires, the excess pressure from the expanding hot water will cause relief valve discharge. On the other hand, there is no problem with having an expansion tank that is larger than what your system requires. In fact, if unsure that your expansion tank will be able to safely accommodate your system, it is common practice to choose an expansion tank that is one size larger than the required size. As a general rule of thumb with expansion tanks, it is better to oversize than to undersize.

 

Plumbing Applications

 

 

Therm-X-Trol

 

Therm-X-Trol expansion tanks are made with non-ferrous materials, which makes them suitable for domestic hot water systems.

 

Characteristics of Therm-X-Trol Expansion Tanks

 

  • Secures the water heater and fixtures

  • Eliminates water and energy waste

  • Assures that relief valves will not open

  • Reduces risky pressure build up

 

Sizing Charts

 

Residential Applications (Up to 150*F)

 

Static Supply Pressure (psi)

Water Heater Size (gallons)

40

50

60

80

120

40

ST-5

ST-5

ST-8

ST-8

ST-12

60

ST-5

ST-5

ST-8

ST-8

ST-12

80

ST-5

ST-8

ST-8

ST-12

ST-25V

 

Model Numbers

 

Commercial Applications (Up to 180*F)

 

Static Supply Pressure (psi)

Water Heater Size (gallons)

40

50

60

80

120

40

ST-8

ST-8

ST-8

ST-12

ST-12

60

ST-8

ST-8

ST-12

ST-25V

ST-25V

80

ST-8

ST-12

ST-25V

ST-25V

ST-25V

 

Model Numbers

 

 

Hydronic Heating Applications

 

Extrol and Fill-Trol

 

Extrol expansion tanks are used far more frequently than Fill-Trol expansion tanks. In fact, the only difference between the two is that Fill-Trol expansion tanks include a specially designed pressure-reducing fill valve. Extrol expansion tanks require a separate fill valve.

Extrol and Fill-Trol tanks are sized with an extra factor to consider. Your boiler will, more than likely, have its BTU/Hr production rate information printed on it. Extrol and Fill-Trol models are sized the same way and are of comparable size.

 

Characteristics of Extrol Expansion Tank

 

  • Provides permanent separation of system water from air

  • Controls and normalizes the water pressure of the system

  • Uses a Butyl/EPDM diaphragm for far better air retention than natural rubber

  • Simple to install

 

Characteristics of Fill-Trol Expansion Tank

 

Doesn’t require a separate automatic fill valve

Same features and model as regular Extrol expansion tank

 

Sizing Chart

 

Type of Radiation

Boiler Net Output in 1000’s of BTU/Hr

25

50

75

100

125

150

175

200

250

300

350

400

Finned Tube Baseboard or Radiant Panel

15

109

15

109

30

110

30

110

30

110

30

110

60

111

60

111

60

111

90

SX-30V

SX-30V

Convectors or Unit Heaters

15

109

15

109

30

110

30

110

60

111

60

111

60

111

60

111

90

SX-30V

SX-30V

SX-40V

Radiators Cast Iron

15

109

30

110

30

110

60

111

60

111

90

SX-30V

SX-30V

SX-30V

SX-30V

SX-40V

SX-40V

Baseboard Cast Iron

15

109

30

110

60

111

60

111

90

90

SX-30V

SX-30V

SX-40V

SX-40V

SX-60V

SX-60V

 

Model Numbers (Fill-Troll Model Numbers in Bold)

 

 

Radiant Heating Applications

 

Radiant Extrol

 

Radiant Extrol expansion tanks are designed to work in both open and closed loop radiant heating systems and are also suitable for snow melting applications.

With Radiant Extrol expansion tanks, another factor to consider in sizing them is the size and length of the tubing you’re using.

 

Characteristics of Radiant Extrol expansion tanks

 

  • Specifically designed for high-efficiency radiant systems

  • Appropriate for barrier and non-barrier PEX systems

  • Befitting for use with glycol

  • Non-ferrous connection that resists corrosion.

 

Sizing Chart

 

Nominal PEX Tubing Size

Length of Tubing (Feet)

1000

5000

7500

10000

14000

18000

22000

30000

3/8”

RX-15

RX-15

RX-15

RX-15

RX-15

RX-30

RX-30

RX-30

1/2"

RX-15

RX-15

RX-15

RX-30

RX-30

RX-60

RX-60

RX-60

5/8”

RX-15

RX-15

RX-30

RX-30

RX-60

RX-60

RX-60

 

3/4"

RX-15

RX-30

RX-30

RX-60

RX-60

RX-60

   

1”

RX-15

RX-30

RX-60

RX-60

 

 

 

 

 

Model Numbers (Radiant Extrol expansion tanks)

 


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