How to size and select a proper Expansion Tank

How to size and select a proper Expansion Tank

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.

• 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

Commercial Applications (Up to 180*F)

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.

• 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

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.

• 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