My son is in need of a new hot water heater for his home. I am trying to advise him on getting an on-demand system.

He has:

- well water
- no soft water conditioning system
- elevated calcium in the water[*]propane gas service

Are there any issues now with using this system with well water?
What may be the better manufacturer/model to look at purchasing?

I can't answer your specific questions but when I was looking into them the general opinions from people that had them was you need two, in series to keep up.

i looked into this kind of setup when i needed a new hot water heater years ago.
at that time, i was advised that for my home use, it was better to buy a conventional water heater because of the cost to payback ratio of the on-demand units just wasn't practical, and there were a couple of other things i didn't think of at the time, but i forget what they were.
i don't know if anything has changed over the years, but at the time i needed one, my local plumber advised against it.

max temp diff is the issue.
they were mostly used in tropical area's overseas, so you don't need that much delta to get hot water for a shower.
but if you get one that only has a 60 degree diff and your water is coming in at 50 degrees, your shower might not get that hot.

Years ago, buddy of mine installed in his house, up here in COLD Alberta. Initially unit did not work well, and had it replaced under warranty, but then paid extra to get next size up . . . still had issues when it was like minus 25 and colder here . . . temp differential kept it from working correctly . . . great when it did work - could fill the hot tub with 120F water with no issue. But during the extreme cold snaps, had to take cover off it to let room temp help keep things warm . . .

Seems units are more designed for warm/cool climates . . . not damn cold winter types.

They depend on how much hot water you use. If it's one person with minimal use it's better then if you've got several people using it and using hot water regularely. You can end up spending more then what you would to run a normal water heater.

Many factors to consider...
Location of the tank
Pipe distance run to the faucets and/or valves
When 1st turned on take a short time for the water temp to go up
Tank/system can be noisy
Overall expense


Just my $0.02...

My buddy has an electric one in his house, it's on three 20 amp 220 breakers that come on in stages as needed. I haven't heard him complain about any issues, but I bet his electric meter really spins if all three circuits are on. They make gas on demand water heaters too.

With the cost of propane - the payback wont be there - I would look at a hybrid heat pump/ electric water heater - they are extremely efficient

I can't speak to the well water comment, but the house I bought 2 years ago has one. The main bathroom is on the 2nd floor and the tankless heater is in the basement. It takes about 30 seconds of running the shower before hot water is available, but it does last indefinitely and I haven't had issues when showering simultaneously with laundry or the dishwasher.

I had a Rinnai tankless unit installed in our house when we built it in 2016.
Initially, I was going to get an electric heater but the electrical demand is quite high when it first fires up, so I went with propane. At the time propane was relatively inexpensive, and that's what I went with.
The heater is about 40 feet from our master bathroom and it takes a minute or two for the water to get hot enough so I don't suffer any major shrinkage. But, once it gets hot, it stays hot until I'm done with the shower.
We're on rural water and it has a lot of calcium in it. So, I back flush the heater every year or so with white vinegar. In fact, that is recommended preventive maintenance for the heater.
During the winter we will see single digit outdoor temperatures, but I have never checked the incoming water temperature. But it is quite cold. The heater still takes about the same amount of time to get the water hot as it does in the summer.
I wish we had access to natural gas for the heater. There are gas wells all around our house but the neighborhood where we live does not access to gas. What's really frustrating is that there is a gas riser valve about 1000 feet from my house, but that pipeline goes to Memphis.
All that being said, I am quite happy with the performance of the water heater.

We have a Rinnai with natural gas in our guest house that is 1,000 sq ft. Water is hot in 30 seconds or less and you can’t hear it run. We have city water, so I I have no feedback on well water. We are very happy with it.

I have an on-demand electric unit in the shop. Hate it. As has been mentioned, they do not produce a fixed outlet water temperature under all conditions, just a temperature rise from inlet to outlet. So if you have a inlet water temperature that fluctuates, you have to size the heater for the coldest inlet. Then there is the flowrate. Unless you get one of the larger ones, the common smaller ones produce about 1 gpm of heated water. Then the maintenance, if you have hard water, buy stock in a vinegar company because you'll be using a lot to descale the heating elements. This is ignoring the current draw that you'll put on your service entrance, for mine if I wanted a good supply of hot water, I'd ended up with 3-40 amp 240 volt breakers.

If I had it all over to do again, I'd gotten one of the conventional small trailer house water heaters and called it good.

Have one in my home with well water for 12 years. Love it and have had no issues. Shower is 30 feet from unit takes about 25 seconds for shower to get hot. My well water is very soft and has very little calcium in it. I also run a water treatment unit. Not sure how one would work with high calcium and no filter system. The cold water in the pipe between the heater and the shower head needs to be purged even with a conventional tank heater so you are not going instant hot water anyway.

I see you're from the north. Is he? Is he married with kids or is there more than just him living in house? How old is his place, and what kind of electric service does he have?

My father and I did a significant amount of research when my parents needed a new water heater. The on demand units just could not keep up with them and what they did on a daily ( shower twice, dishes, laundry), we opted for a Rheem heat pump unit. They love it. We were going to put a booster on it as well, but after a month of use, they decided it was not needed.

At the time, the price was about $1600. He used the tax time rebates and incentives that were available and it wound up costing him $400 total out the door, with me adding new plumbing as well.

He is in Northern Michigan near Kalkaska. He has a 1100 sq. ft home, 2 bathrooms. He is not married....yet.

I saw this video: https://www.youtube.com/watch?v=AsR8n-oknhs

it looks like a bit more research on the connectivity elements are needed. But at 5 gpm, that looks like more than enough for this home.

The house was built 11 years ago. However the guy that built it was not the best educated builder. I am having to repair all the screw-ups he made. His buddy was the building inspector and I believe he signed off on the final inspection without ever looking at the house.

A new heat pump water heater will pay for itself in about 3 years and most likely can get rebates from both tax and utility. They are the cheapest to run by far.

People lucky enough to live where its hot enough to have them in a garage also gets the benefit of them acting as an AC and it will cool the garage.

I have an Electric On demand that I heat my shop with (radiant floor heat) and have had no issues with it in 10 years. From my investigations,
- On Demand water heaters should be sized by demand - making them very efficient (not a one size fits all situation) You can install one large whole house demand but it reduces the benefits and increases the total overall cost.
- Often multiple smaller electric units are installed at the point of use (each bath, kitchen) this lessens the lead time for hot water minimizing water waste and allowing for smaller elec circuits per unit .
- depending on the mineral make up of your well water it may be an issue with deposits building on the element(s)/exchanger.
- My heater has an output water temperature sensor, up to 135degF.
My opinion is they are superior to tank type heaters but may require different maint. My system is closed loop and filled with deionized water so build up form impurities is not an issue.
I would not try to use one on my well water based on it mineral content (Hardness Is greater than 10gpg, high in calcium content).

If your area experiences frequent power outages. A tank will supply hot water for a time during the outage. Or all the time if you have a gas.

A propane/NG heater still requires power to operate, just not much. Some people even use battery backup, I use my home generator.