(A neighbor mentioned that there is some sacrificial part that can be replaced every so often to extend the life of the tank.)

It's called a sacrificial annode. It's purpose is to attract all the rust to it'self to prolong the life of the tank. They're supposed to be replaced every 3years or so, even more frequently if you've hard watter.

Most people don't know and have never checked. If it's been more than 5 years, it's probably just a thin red mud at the bottom of the tank. (one of the reasons water is drawn from the top).

I replaced my gas water heater with a heat pump water heater. It's great! I live in a humid climate and having the extra cooling/dehumidifying in the summer is a great bonus. It does make the basement noticably colder all year round though. The energy/financial savings are essentially, I get free hot water in the summer, and a little extra demand for heating the house in the winter.

Recovery time is not really noticeable unless we have company staying with us. My Rheem unit has a "High Demand" mode that kicks on both the heat pump and resistive elements to provide recovery comparable to a gas heater.

The old heater was end of life and the local incentives made it cheaper to install a heat pump water heater than any other type. 15-20 years is considered end of life, most warranties only go to 10 years.

Most tank water heaters have a sacrificial rod or two regardless of heat source

Tankless water heaters are really only practical with burning either oil or gas, the main benefit being you'll never run out of hot water.

Undecided with Matt Ferrell has a good video on heat pump water heaters Technology Connections has a good video on home electrification

Edit: find a contractor(s) who know how to work with local incentives. Federal tax credits were ended by the "Big Beautiful Bill" last year.

If you don’t live in a hot climate, many heat pump water heaters take heat from indoor air. Be aware of that - you’re heating air, then moving that heat into the water tank. It really drops efficiency. But they’re almost certainly a lot cheaper to run long term than paying for oil deliveries! They’re not necessarily cheaper than gas, because gas is just so cheap. I’d be wary of replacing a working system, because it’s probably not going to break even, but check for incentives that might help with the cost.

If you make the investment, a water softener could be a good investment. Draining/flushing and maintaining the anode rod is a big factor in longevity.

Tankless is ok, but it burns oil or you need pretty serious electric service. One downside is that the hot water piping doesn’t get the heat transfer from the tank of hot water so the whole pipe length cools fairly rapidly; 1hr between showers and you need to run the tap for a while.

I believe that a heat pump boiler should have backup electric heating elements that kick in when there’s high demand or if it is too cold for the heat pump to keep up.

Pitfalls:

You have a small space: heatpumps need airspace and it needs to circulate. An enclosed closet won’t work.

Your heater is outside: heatpumps pull air through and dust/cobweb buildup isn’t good.

You dont have electricity to the heater: heatpumps need a decent cuirruit size to run. Some can run off a small 120v circuit.

You didn’t size right: heatpumps can’t keep up with sustained demand usage. A larger tank offsets this.

You can keep your old system too though. Just put your hybrid before it and set your temps at like 125 for the heat pump and 120 for the boiler. Your boiler will rarely need to run unless you have sustained usage, a power failure, or it needs to bring temps up in the water it’s holding.

Yes but make sure you get a really solid labor warranty. We got a State branded hybrid water heater and the heat pump failed in the first year. Had it failed after one year we'd be on the hook to pay foe the labor to replace it even if the water heater itself was covered under warranty.

Thankfully the replacement has been flawless so far, hopefully it was just a fluke.

It's so neat walking into the utility room and feeling the air is noticeably cooler and dryer, especially with my modest almost-homelab setup in the same room. I love being able to feel that its doing its thing, and that's also how I knew the previous one had its heat pump fail, it was immediately obvious when walking into the room after no hot water.

Even when the last one failed, it was one button press to make it fall back to the resistive heating (I run mine in pure heat pump mode full time) and that worked perfectly fine until the replacement installation

We swapped last year. Getting hit with several big oil bills every winter sucked, and the price doesn’t really go down.

Oil furnace hot water baseboard heat - yearly boiler cleaning and maintenance, oil filter changing, complex issues like valves, pumps or whatever that we’d had that probably averaged easily a couple hundred a year in preventative and actual maintenance. Roar under the floor when the unit kicked on. Negotiating delivery schedules and price contracts with heating oil services. Colder than normal and need an earlier delivery? Fee. Takes a while to warm the house up due to needing to heat the mass of water and circulate. Got rid of a big boiler, pipes, and fuel tank.

That said, I found the baseboard heat very comfortable and uniform during winters. I miss that slow, even heat sometimes.

Heat pump system - removed our built in AC handler and installed the heat pump unit, forced air, used existing ducting from AC. Got several thousand in incentive rebates from the State to install the efficient units. Covered installation costs easily. Maintenance is far easier, I swap a HEPA filter every 4 months or so myself. Quiet operation, quicker heating or cooling. Love the dehumidifying feature during summer, it gets really humid.

Downsides: drier air in the winter, we now run a regular ultrasonic humidifier in the winter, but could have installed a whole-house humidifier with the unit. That would have cost thousands more. The unit is the “extra” efficient version that is supposed to run down to -20. Wouldn’t you know it, this was the coldest winter for the longest stretch we’ve had in forever, and the unit struggled. We did not install the “heat strips” that would have added more heat in such a situation. Again, thousands $ more.

And of course the electric bill is higher. I would say that the additional electric cost compared to the overall oil cost, maintenance, and contracts for the oil furnace is lower. Not ridiculously lower, but the heat pump system is clearly a winner as far as cost to operate.

Summing up…Get a good heat pump for your climate. You will realize savings and a reduced headache for maintenance. However, it isn’t a miracle solution.

I'm going to assume a solar heater isn't n option where you live. I've got that on the roof works great where I live, basically no energy cost once you install AFAIK (I rent)

If you live in the US, power company and tax rebates make it much more attractive to get a heat pump water heater.

If you live in a warm climate, you can add a duct to the water heater exhaust to move the cold air somewhere warm, like a garage or an attic.

What is your goal? To save money? How much more does a heat pump cost? How quickly will the energy savings add up to the difference? How much more expensive and frequent will maintenance be?

You may not need to plan for a larger capacity. Many of the new heat pump water heaters over heat the water, then mix it back with a little cold before sending it to the taps at your desired temp. You get something near 75 gal out of a size 50 tank.

https://www.bchydro.com/powersmart/residential/tips-technologies/heat-pumps.html

Your local energy provider might have info on that.