When to Replace a Water Heater?

When it starts leaking.  Or when the heating element or thermostat stops working and you don't want to replace them.  They are replaceable but doesn't make sense to replace after 5 years or so.  I have a gas hot water heater in the states that's 24 years old and shows no signs of trouble.  I replaced the anode rod  about 10 years ago, it was gone.  I replaced my 10 year old electric unit on STX last year when it started to leak.

If you're replacing it, you should consider a solar hot water heating system.

It might cost more upfront, but, will save you thousands in the long run.

Most people replace their water heaters when they start leaking.  This, however, can result in excess water damage if you don't discover the leak fairly early or if the leak happens to be a catastrophic one.  

So, it is wise to inspect your eater heater on a regular basis and if you detect a small leak tending to it quickly can extend the tank's life.  You should also shut the unit down and drain the tank at least once a year.  This will remove any silt buildup and retard internal corrosion and rust which are two of the main causes of leaks. 

As previously pointed out water heaters have a life expectancy of somewhere between 8 and 12 years but that's only a guideline.  In 15 years living in the Caribbean I've had to replaced mine twice so I'm on my 3rd one and it is beginning to show it's age even though it's only about 4 years old.  We just replaced the water heater in our stateside condo after 12 years as a preventative measure.  It wasn't leaking but as the plumber was removing the old unit it became apparent the area around one of the fitting was so brittle and rusted it could have burst any moment.    

you may want to look at an on-demand unit.  According to Energy.gov, “For homes that use 41 gallons or less of hot water daily, demand (ortankless) water heaters can be 24% to 34% more energy efficient than conventional storage tank waterheaters.”  I think this is my plan going forward.

https://www.petro.com/resource-center/tankless-hot-water-heaters-vs-tank-storage-water-heaters

Just be aware you will need to run a larger power line or gas line to a tankless on demand water heater.  You would need a very small tankless unit with little capacity, i.e. flow,  to fit on your existing water heater power line/circuit breaker.

Yes, you will most likely need to convert the line to 220, but otherwise a better long term solution.

220, 221 whatever it takes.  Most likely existing water heater is already on 240.  But your existing 20A wire an circuit breaker will not be big enough for tankless.

Agreed, but you can run a new line as long as you have 2 spaces in your box, it's not hard to do.  The biggest issue in USVI is the concrete construction, so depending where your current water heater is and if you have the ability to snake a new wire to the unit, it's not an overly complex project.  I've done a lot of my own electrical, so I would be able to accomplish it, some would need an electrician.  Just making a suggestion on the tankless unit due to energy consumption and longer lasting.  But for ease, just replace your existing unit.

Add a timer to your water heater.  I had my Electrician install mine.

That way you can save significantly  in your electric bill. No reason to have it run 24/7/365. I run mine 2 hrs. a day and have plenty of hot water.