Way, way more expensive. I have around a 4000 sq/ft house with two teenagers still at home and the usage portion of my gas bill in the summer with a 60-gallon gas tank is around $12/month. There is just no significant savings available with a tankless, and electric is much more expensive.
When I ran the numbers, it looked like a gas water heater would cost me about $300/year and the electric about $400/year. This is with Mid America rates.
If it breaks and leaks, is it is a spot where there is a low point drain or will it flood? If floods, then I would probably replace.
The way I've always dealt with them, is when they've got to that point, I just set aside funds and timeline to replace it. I'd rather have it replaced on my timeline rather than doing it in a hurry when no one has any hot water.
The floor slopes into a drain where it sits, so I'm not too concerned about it flooding
If u have access to a decent plumber with fair pricing, then I would ride it out.
Main thing to check periodically is if your relief valve works.
Part of the conundrum is that most of the newer stuff doesn't seem to have the longevity of the older. Replaced the washing machine on the main floor twice since our build and the old machine from our previous home is still functioning in the basement. The old one is used mainly for rugs, heavily soiled work clothes, etc. while the main floor one is used primarily for finer things/lighter loads.
Gas is cheaper on day-to-day basis but will be replacing it 6-9 years. Tankless needs ongoing maintenance(yearly) to get the full life out of it and can be very expensive for repairs. Electric day-to-day cost will be higher but it will run for easily 15+ years. You can also just replace parts on a electric water heater very straightforward and easily available. Just pulled one of a property that was 23 years old and only did it because the bottom was rusting out.
Limitless hot water is the huge advantage of a tankless water heater. No pressure issues or energy wasting with tankless. A few dollars more than a tank, but I like the change.
Some years ago when my tank heater went out I was set on tankless. The plumber talked me out of it, even though he said it meant significantly more $ in his pocket. Then that was all reinforced when I talked to some friends that went to tankless too.
