You’ll need:

  1. A 12” adjustable wrench and a pair of channel locks or a pipe wrench;
  2. A new temperature/pressure relief (TPR) valve;
  3. Teflon tape to seal gas pipe connections;
  4. A dolly will make moving the heaters around a LOT easier.

Be aware: if pipe connections are soldered, unless you know who to sweat copper, you might want to leave replacement to a plumber.

Follow these instructions carefully (you're dealing with gas) and use the photos for reference:

  1. Locate the main water supply valve to the home!
  2. With an adjustable wrench, shut off the gas BEFORE disconnecting the gas supply pipe at the water heater;
  3. Turn off water supply to the heater;
  4. After turning off the hot water supply valves to each plumbing fixture in the home, open all the hot water faucets. This will help the water heater tank to drain. WARNING: if these valves are old they can fail or leak when they’re operated. Be ready to shut off water to the home and replace the valve or call a plumber;
  5. Attach a hose to the tank drain and drain the tank. Typically discharge hot water somewhere safe outside. This will also empty the hot water pipes so they won’t dump hot water everywhere when you disconnect the hot water pipe from the heater.
  6. Disconnect the draft hood and the TPR discharge pipe (which you’ll probably re-use.
  7. Disconnect the water supply lines/pipes and the expansion tank from the water heater. Use a wrench on the fitting while turning the expansion tank so that you don’t compromise the soldered fitting connection and cause it to leak later. If the expansion tank is old and corroded you may need to replace it.
  8. Haul the old water heater away and put the new one in its place.
  9. Reconnect the water lines, the expansion tank, and the draft hood. Use the Teflon tape on the threads
  10. Install the new TPR valve (very important safety feature!) and attach the TPR discharge pipe.
  11. Reconnect the gas lines, use Teflon tape.
  12. Open the water supply valve at the heater and the valves at plumbing fixtures and turn off the hot water faucets at fixtures.
  13. Turn the gas supply back on and follow the manufacturer’s instructions to relight the water heater burner.