Turn off the water heater power or gas supply
Shut off the cold water supply to the water heater
Open a hot water faucet to relieve pressure
Drain a small amount of water from the tank if needed
Confirm the expansion tank size matches the water heater system
Wrap the tank threads with plumber’s tape
Install a tee fitting on the cold water line if required
Mount the expansion tank on the cold water supply line or above the heater
Tighten all threaded connections securely
Support the tank properly with a bracket or pipe support if needed
Restore the cold water supply
Check for leaks at all connections
Reopen the hot water faucet until air is purged
Restore power or relight the gas supply
Verify the expansion tank is operating correctly