ET-15 Expansion Tank Specifications

Expansion Tank Features:

• Steel construction
• Rugged flexible Butyl diaphragm separating the air chamber from the water containing chamber.
• Precharged at 12psi (82 kPa)
• Compact size saves space and energy
• Compatible with glycol in systems

Expansion Tank Models:

• ET-15 - 1/2" male connection and tank volume of 2.1 gal.
• ET-30 - 1/2" male connection and tank volume of 4.7 gal.
• ET-60 - 1/2" male connection and tank volume of 6.6 gal.
• ET-90 - 3/4" male connection and tank volume of 13 gal.

Watts Series ET non-potable water expansion tanks may be installed in a tee or any other suitable tapping in the heating system and can be installed in a vertical or horizontal position.

Note: tank must be supported when installed in a horizontal position.

Expansion Tank Dimensions:

• Connection size: 1/2" male NPT
• Total volume: 2.1 gallons
• Acceptance volume: 1.4 gallons
• Diameter: 7-13/16"
• Length: 11-13/16"

Watts product specifications in U.S. customary units and metric are approximate and are provided for reference only. For precise measurements, please contact us. Watts reserves the right to change or modify product design, construction, specifications, or materials without prior notice and without incurring any obligation to make such changes and modifications on Watts products previously or subsequently sold.

Expansion Tank Pressure - Temperature Ratings:

• Maximum design temperature: 240°F (115.5°C)
• Maximum design pressure: 60psi (413.7 kPa)
• Hydrostatic test pressure: 75psi (206.7 kPa)

Expansion Tank - Materials:

• Nipple: steel
• Tank: steel
• Diaphragm: butyl

Selection Guide for Captive Air Expansion Tanks

Expansion Tank Selection guide
As an alternative to using a formula, you can use this Quick Reference Sizing Chart to select the correct tank for your system.

This simple table is based upon a tank pre-charge of 12psi (82 kPa), a pressure relief valve setting of 30psi (2 bars) and a system operating temperature of 200°F (93°C).

The chart takes into account typical system water volumes based upon boiler BTU's and type of radiation with larger volumes of water installed, such as cast iron base board or radiators.   

Watts Series ET Non-Potable Water Expansion Tanks for closed loop hydronic heating systems. 

Heating System Expansion Tanks - ET15 by Watts

ET-15 Heating System Expansion Tanks Non-Potable

Control thermal expansion in hot water heating systems with heating system water expansion tanks.

Thermal expansion of heated water may occur wherever water is heated in a closed system (when the boiler water is isolated from the public water supply by a one-way valve, such as a feed water pressure reducing valve, backflow preventer, check valve, etc.).

The Watts Series ET Non-Potable Water Expansion Tanks are designed to absorb the increased volume of water caused by thermal expansion and maintain a balanced pressure throughout the hot water heating system. They are used to prevent system damage and unnecessary relief valve discharge caused by excessive pressure from thermal expansion.

ET Series Non-Potable Water Expansion Tanks are designed to absorb the increased volume of water created when the hot water boiler is heated and to keep system pressure below the relief setting of the relief valve. Series ET is a pre-pressurized steel tank with an expansion membrane that prevents contact of the water with the air in the tank. This prevents loss of air to the water and ensures long and trouble-free life for the system.

"New boiler water", or water being admitted into a closed heating system, is oxygen-rich. New water is admitted to boilers automatically via the automatic water fill valve when the valve senses low water pressure in the boiler. This "new water" is harmful to all ferris (iron) parts in the closed loop system. Under pressure and temperature oxygen is bubbled or "squeezed" out of the boiler water but that takes time. During the time that the oxygen-rich water is in contact with the iron parts in the system, that oxygen and water is rusting those components from the inside out and this all can happen surprisingly fast. The clue that you have to this situation is the leak!

The point here is, if you have a leak in your boiler system, like a relief valve that is dripping water, it is important to get it fixed or you can expect major problems which can often be the loss of your cast iron boiler sections from oxygen induced internal erosion. The result will be that the boiler will leak and cannot be repaired because the metal is gone. The cast iron sections actually would need to be replaced because they have turned to rust. Sometimes at this point, the least expensive route would be to get a new boiler.

Tip: A leaking relief valve on a boiler is often a symptom of a bad (failed) expansion tank. If the relief valve leaks and the tank is "bad" waterlogged, the proper action is to replace both the tank and the relief valve.

For a link to the specification sheet in PDF format, please click here.
For a link to the installation guide in PDF format, please click here.