Hello: I’d like to preach a little and then answer your questions :cool:. Safety is VERY important to me/us. Information in the hands of someone who may not have the proper foundation to put it on can be a deadly thing. If you’re not familiar with plumbing there is no shame in getting the help of someone who is and then telling them exactly what you want done. Now let me hop down off my soap box…
1. Yes. The water level in the heater needs to be lowered a little and there must be no pressure.
2. Open a hot tap and use the heater drain to remove some water. The relief should be tested periodically, but with the knowledge that it may fail the test and start leaking– needing replacement.
3. Worry :shock:! That means there is water pressure in the tank.
4. Done right, you should not even get wet except for the water on the old anode. The heater should be turned down to the pilot position whenever the water supply is off.
5. If you run low or out of hot water during your shower than your heater is not meeting your needs. Normally a 40 gallon gas heater will supply a family of four. You can measure shower head output by collecting the water for 30 seconds, measuring it and doubling that number. That is your gallons per minute or GPM. You get roughly 75% of the volume of your heater as undiluted hot water.
6. It is the incoming cold water that pushes hot water from the tank, so yes, the tank stays full.
6.5. Recovery rate is decided by the size of the burner and number of gallons, but as a very rough approximation, one half hour is a good “time to reheat” guess.