Two things I want to add to this discussion.
(1)
Legionella: I did an experiment today. I turned the thermostat to about 140 degrees (it only has markings for 125 and 150). The water heater is in the basement, which is about 45 degrees. I had not used the heater for about two weeks. I ran the heater 1h 15 min. The temperature at the kitchen faucet was 130 degrees. I ran the heater another 15 minutes and the temperature at the faucet was 140.
So total 1 hour 30 minutes to reach 140. Research shows that to kill Legionella it takes 140 degrees for 32 minutes. Granted, the temperature at the faucet is lower than in the tank. Still, this experiment shows that with a cold tank, it takes a fairly long time to heat the water to 140 for 32 minutes---perhaps 2 hours.
(2)
My new plan: I opened up the panels on the heater and found that it only has one thermostat, at the top. I'm thinking of disconnecting the lower element. I think the top element would provide enough hot water for a good shower.
Two questions: (1) Do you see any problem with this plan? (2) Can I disconnect the lower element myself? How would I do that? What would I need to be careful about? (Response: Turn off the breaker.
)
I have some R30 insulation that I plan to wrap around the tank and put on the top. I will also insulate the pipes. The I'll turn the water heater on for one month and see what my electric bill is.
This will be in lieu of the best solution, which is to get either a smaller tank or an on-demand heater.