How do you choose a thermal expansion tank?

When choosing a thermal expansion tank, consider the system's water heater capacity and the type of system (closed or open). Calculate the required tank size based on the heater's capacity, typically using a sizing chart or formula provided by the manufacturer. Additionally, ensure the tank's pressure rating matches your system's pressure and check for compatibility with your Plumbing materials. Lastly, consider the installation space and any specific features that may be required, such as a bladder type for better performance.