On-Demand Water Heaters - Pros and Cons

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.

Unless you have a direct vent with no electronics.

Yes! The other benefit the parents experienced was much, much longer life out of the dehumidifier they had to run nonstop and empty twice a day. Now the heat pump h20 heater takes the majority of the moisture out of the basement. BUT- as mentioned, it does have a cooling effect on the area its placed in.

Interesting discussion.

I had not thought that in some homes you can “tweak” the HVAC somewhat.

Upper floors of a home tend to be warmer.
In some instances a heat pump water heater should be upstairs?
( maybe in an attic? )

When I had an all electric on demand hot water heater around year 2000 I had to let a pencil sized stream of hot water flow in the sink to take a shower without wild fluctuation in shower temperatures.

When I was in England (in the USAF), one house we were in had a system with a small (probably 10 gallon) tank-type hot water heater for the sinks and washer, and a wall mounted on-demand unit next to the tub for it and the shower. This unit was about 12"w x 18"h x 4"d. and had an on-off switch and a temperature dial. When you flipped the switch you got almost instant water at the temperature dialed in, forever. I've seen similar point-of-use heaters on Amazon, but as stated in other replies, they only advertise a temperature rise above inlet. With England's temperate climate, inlet temps didn't vary enough to really matter. With utility costs in Europe, it seemed to be an economical way to get the best of both worlds.

We have a Takagi Jr heating our shop floor at the farm for at least 12 years and never had an issue with it. Building is 60x80 and once concrete is warm it hardly runs. I am pretty sure someone bought Takagi.
I am single and got tired of the hot water heater rotting out and put in an A.O. Smith on demand with propane. That was about 5 years ago and never had any issues with it. Even had a hot water tank go bad under warranty and the installer would have had to order one and I would have had to pay shipping. That was about as high as just getting a new one.

They bought one at work. It sucks. The water gets pretty warm. But it never gets so hot you can not hold your hand in it non stop
That was set at max. It would never be good for washing dishes. A quick shower maybe. But not for dishes

I've replaced several tank style water heaters over the years just being the family handyman. Moms house, brother's house, in law's, neighbors, and a few of my own. I've had 2 houses of my own over the years about 30 miles from my relatives and my current one is 6 miles from my 1st. When Ive put them in up north for my relatives (again only 30 miles from my place) they last way beyond the warranty rather easily. .
Here I haven't had one last thru the warranty yet. I buy the 12 year ones. Once I got a 9 year ("middle of the road" quality) and it didn't make it to the end of the warranty either. At least the replacements have been free.
In both of my houses I came in to find a 30 gallon tank and upgraded to 40 gallon models. All nat gas models. And un both of my houses the units I removed were removed just because they "looked old" weren't leaking yet. I'm sure the one I p put in this house in 98 replaced the original which was from 1967. And I'm on my 3rd water heater. The last one that went lasted about 7-1/2 years.
. When that one went, I took my replacement credit (which was alot more than I'd paid for the 1st one I'd put in, that 2nd one was also a free replacement for the 1st one I bought) and put it towards an AO Smith wall mount tankless, since they were on a good sale so I didn't have to add much to make up the difference in price between the current value of a 40 gallon tank and the tankless.
My biggest reason for the tankless is that where the water heater was located it is directly in front of the furnace, with not a whole lotta room in between in order to reach the furnace when it needs maintenance. I've had to remove the tank type water heater a couple of times over the years to access the furnace, then Reinstall it. With the tankless off of the ground I have a lot more room to get at the furnace. So far I like the tankless. It's been in place about 2-1/2 years so far and has a 15 year warranty.
Hopefully now that we have "city" water that will make a difference in helping this one to last. Though we had the same source of city water at my old house too.we had well water when I moved here.

I have had one of these https://www.ecosmartus.com/ for about 8-9 years now. It is the 18,000 BTU mdl. 1200 sq ft house , 2 baths. It replaced a 40 gal electric heater. We have lime deposits in our water. I installed 2 sediment filters the the inlet side of the hot water heater and a filter on the outlet side to catch the lime scale deposits. I change the filters every 12-18 months. if you want to be able to use hot water at multiple locations at the same time. I would get the bigger unit 24,000 I think. But this works well for just the wife and myself. As stated it is nice to have unlimited hot water. The is no doubt in my mind that it paid for itself in 3-4 years. My electric bill went down considerably.