On May 29, 7:29 am, Michael wrote:
We have an old AO Smith 40 gallon gas water heater which seems to have
some leakage issues.

We have been anticipating replacing it for some time now but I need
some advice.

There are five of us in the house (including my 15 year old daughter,
who takes very extended showers!)

The current unit seems to poop out after 2 or 3 showers and we will not
run the dishwasher or washing machine in anticipation of showering.

For a new unit, should we go with a larger unit (75 gallon) or are we
better off with a smaller 50 or 65 gallon with a faster recovery time?
What about the "instant," tankless water heaters?

What gives the best performance, balancing efficiency and hot water
availability?

I went through this a few years ago, only 4 in the house but 2 of them
teenagers. I went with a 50 gallon gas-fired conventional water
heater and it has served us well. No hot water availability issues in
practice, although I suppose in theory it could happen through
coincident heavy usage. That is, I wouldn't guarantee that it would
never happen, but in practice it has been fine. Your old unit may be
limed up and in fact have less capacity than its rating.

When my daughter took showers I used to shout through the door, "leave
some water for the fishes in the sea."