On demand water heater

We currently have a 50 gallon water heater run on natural gas... it works, but there have been a couple times that we've run out of hot water when doing successive showers... so we've decided to have a Rinnai installed like we had at our last house
.
After going to the Rinnai site https://www.rinnai.us/residential/solution-selector and answering the questions we decided that the maximum number of 'fixtures' we will ever run at one time is 3 and most likely fewer, but we don't want cold water in the shower again (3 fixtures could be dishwasher and clothes washer and the shower... probably not all at the same time, but cold water in the middle of taking a shower is really bad)
.
I am an Army veteran so I get a small discount at Home Depot... as soon as our plumber visits to be sure what we want to do is possible I will place an order... the Rinnai is listed as .98 efficiency so I think we'll even get a deduction on next year's taxes (when we had to replace our DEAD furnace last year we got an energy tax deduction due to the new furnace being much more efficient)