Most thermal expansion tanks manufacturers will call for the tank to be installed in the vertical position and properly supported. They type of support required for the expansion tank will vary with the piping in the house.
Copper supply lines can support a standard 2.1 gallon expansion tank. However you should ensure the copper tubing is connected properly.
Pex supply lines make for an easy addition to the expansion tank. Be weary, without additional support you could have issues in the event the expansion tank fills with water. A copper t is usually the best way to setup proper bracing.
Posted in: Thermal Expanion