tankless vs. tank hot water heater in place with "hard" water

nt101

We live in Cambridge, MA which is known for its very hard water. Our water heater is basically caput. I'd like to upgrade to tankless given the energy savings (the state gives a $750 rebate vs. $100 for regular water heater), but am not clear on the cost-benefit here. It seems tankless have higher annual maintenance costs and more likely to have problems, which may or may not outweigh the energy savings, although my understanding is these tankless units last 3x as long as a regular tank but are also about 3x the cost. What should be the factors that we use in making the decision? As experts, what are your experiences with each of these systems?

Also, I searched through the forums here, and found one post directly on "should you install tankless" (https://heatinghelp.com/heating-museum/tankless-water-heaters/) but I couldn't immediately find more although I am sure they are out there. I apologize in advance if this topic has already been addressed; please do point me in the right direction if that's the case!

SuperTech

Tank style water heater. Without question the best choice when dealing with hard water. We have hard water in my area. All tankless boilers, coils and mod con combi boilers require high maintenance. A boiler with an indirect tank or direct fired tank style water heater is the preferred way to go for reliability.
I certainly don't see tankless lasting three times as long, unless it's a cast iron boiler with a tankless coil. And in the lifespan of the boiler that tankless coil will see a flush with Sizzle every few years depending on the severity of the hard water. Usually these coils need replacement after being hit with Sizzle more than twice.

Jellis

Some good information here
https://www.petro.com/resource-center/tankless-hot-water-heaters-vs-tank-storage-water-heaters
The key i think in the article is
"less than 41 gallons per day"

It certainly doesn't provide any advantages over a storage water heater as far as your hard water is concerned. Bad water quality can definitely mess with any heater.

SuperTech

@Jellis you don't think the Tank water heater is more reliable? Build up of scale will wreck the efficiency of either, but a tankless will be rendered useless much quicker in similar situations where no service has been done.

Jamie Hall

Tank style. Hard water is really tough on the small passages used, of necessity, in a tankless, and you'll be cleaning and descaling it several times a year.

As to longevity... With decent maintenance, it will be at worst a toss-up -- and the maintenance on a tank type water heater is pretty simple (and inexpensive!). The water heater in Cedric's home has been there for 15 years, and shows no signs of failure yet (tank type, oil fired).

bob eck

If you have hard water you need to treat the water.
With Soft water and flushing the heat exchanger once a year the tankless water heater can last 10 - 20 years.
With Soft water and flushing the tank and replacing the anode rode every two years the tank type can last 10-15 years.
Hard water can void warranty on tankless gas water heaters.

GroundUp

bob eck said:

If you have hard water you need to treat the water.
With Soft water and flushing the heat exchanger once a year the tankless water heater can last 10 - 20 years.
With Soft water and flushing the tank and replacing the anode rode every two years the tank type can last 10-15 years.
Hard water can void warranty on tankless gas water heaters.

Meh.... I can think of 7 tank style units off the top of my head on hard water and a few more on soft that are well over 20 years old that have never once been flushed. 3 of which I am 100% certain have the original anode as well. There's an electric AO from 1993 in one of my rentals that's got water so hard you can't even drink it and I finally replaced the original anode about 3 years ago. Heck, the one in my own house is 11 years old and has never been touched.

On the same note, I've thrown away a dump truck load of tankless from a 10 mile radius here that were scaled up so bad they couldn't even be cleaned. They guy that installed all of them only started in 2012 and has since gone out of business so none were more than 6 years old

SuperTech

Anode rod every two years seems like a bit much. I've seen some good afternoon five years, some almost spent. I don't remember seeing any manufacturer recommending replacement of the anode rod that frequently

Gordy

My area is 28 grains......like showering with agg lime.

Jamie Hall

As I said above, a lot of it is in the maintenance. A tank type heater, even on hard water, should last at least 10 years; 15 to 20 for the higher quality ones. If there is sediment in the water, it needs to be flushed out perhaps once a year. A tankless, with its narrower water passages and higher heat transfer requirements, must be descaled, and the frequency will depend on how hard the water is. If you have a water softener (I can't stand softened water, by the way -- but that's a personal thing) you can perhaps get away with descaling once or twice a year. If the water is hard, you may be looking at once a month. If you are faithful about doing that, it may last 10 to 15 years too.

bob eck

When contractors install tankless gas water heaters are they selling yearly maintenance agreement where you will come back to flush it out once a year?
When selling the tankless gas water heater you could add into the sale price that you will come back in one year and flush the heat exchanger. Show the customer the crap that comes out of the heat exchanger. While you are there check the venting on the TGWH. When the home owner sees the service you provide give them a cost to come back every year to do the same thing. Not only will you keep their TGWH running fine you are always back in your customers home and most likely they will use you for future business.
You can provide the same service for tank type heaters. PVC vented water heaters the venting should be checked yearly and you the professional contractor can provide this safety service to your customers.

Any tankless gas water heaters installed when they have hard water the unit will fail because of scale build up inside the unit and when this happens the unit will use more BTU and run longer then nessary to still make the hot water you need. The extra heat will stress the heat exchanger and cause the heat exchanger to leak. This is not a manufacturer defect it is a result of not softening the hard water.

Is anyone installing the Aquapure Cumo 3M AP430SS filer on the cold water inlet going into TGWH? This filter does not soften the water but it will coat the inside of the TGWH and help prevent the build up of lime scale.
I sell this filter to contractors who install TGWH and this filter work s great on coils in boilers for people that get their domestic hot water from their boiler.

Check it out at Aquapure 3M search AP430SS

SuperTech

I like to see the scale stopper on all DHW equipment in my area. I use one on my indirect. They are a must on systems with plate heat exchangers.

Jellis

SuperTech said:

@Jellis you don't think the Tank water heater is more reliable? Build up of scale will wreck the efficiency of either, but a tankless will be rendered useless much quicker in similar situations where no service has been done.

Yes i agree with you, I was trying to simply state that switching to indirect is NOT better than a tank for dealing with poor water quality. I did not want him believing that the tankless would be better for dealing with poor water. It certainly is not.

the screen on the inlet and various sensors and valves will not like the scaling for sure.

Larry Weingarten

Hello, You might look into condensing tank type heaters like Vertex or heat pump heaters. You’ll get the efficiency (which you want if you use a lot of hot water) and the benefit of relative simplicity.
Yours, Larry