Estimated reading time: 6 minutes

What is a Thermal Expansion Tank?

A thermal expansion tank is a pressurized bladder tank. The tank has a 3/4″ male IPS connection on one side. The opposite side of the tank has a Schrader valve. A Schrader valve is a pneumatic valve. Most tires have Schrader valves. The tank comes pre-charged with air from the factory.

Does My Home Need A Thermal Expansion Tank?

If your water comes from a municipality or a community well then you have a water meter in your front yard. A water meter has an integral check valve. This check valve lets water flow in but not out. Therefore, the check valve makes the home’s water system a closed system. If your home has a closed water system, with a tank-type water heater then a thermal expansion tank is required.

How Does A Thermal Expansion Tank Work?

An Expansion Tank is a pressurized bladder tank. Because air compresses it works well absorbing pressure. As your water heater sits all night long while you sleep it reaches its maximum temperature. As the water becomes hotter it expands. The thermal expansion tank absorbs this expansion.

Where Is A Thermal Expansion Tank Installed?

I Install an expansion tank on the cold water line before the input of the water heater. However, it is best to install it between the water heater’s cold water inlet and the water heater’s cold water isolation valve. In this way, the water heater is protected from thermal expansion when its valve is closed.

How Can I Test If A Thermal Expansion Tank Is Good?

The tank typically fails in one of two ways. 1) It rusts out. The integrity of the tank becomes compromised. It leaks. 2) The bladder ruptures or tears. The tank fills with water. It no longer provides thermal expansion protection. You can test if the bladder has ruptured by quickly tapping the Schrader valve. If water comes out then the bladder has ruptured. The tank has failed. It should be replaced.

“Good Plumbing” A Superior Example Of How To Install A Thermal Expansion Tank.

A Tank Mounted With A Drop Ear Ell Fitting

I Install a tank with a 3/4″ drop ear ell fitting. I drive three screws through the drop-ear ell mounting tabs into a joist for a good strong mount. If the tank fails the drop-ear ell will support its weight.

“Bad Plumbing” Examples Of Poorly Installed Thermal Expansion Tanks

A Tank Mounted With Perforated Strap Iron

Tanks mounted with perforated strap iron are by far the most common scenario. This type of mounting has minimal support. A tank mounted with a drop-ear ell is far more securely mounted.

A Tank Resting On A Water Heater

A Tank resting on a water heater is also a common scenario. This is not ideal. The only thing holding it in place is the connection to the plastic water piping.

A Tank That Is Supported By Plastic Water Piping

This tank has been installed by connecting it to plastic piping. This is by far the worst installation scenario. When a tank bladder ruptures and fails the tank fills with water. A standard 2-gallon expansion tank will weigh over sixteen pounds when filled with water. A similar weight to a bowling ball. This is truly an accident waiting to happen!

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