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Descaling a tankless water heater

Dear Voices of Experience,

I live in an area with hard water. When I bought the house 30 years ago, there was a water softener. It's still here, but I haven't used it for 20 years. It used an awful lot of salt and I didn't like the idea of always having additional sodium in my water. I've gotten used to regularly scooping calcium sediment out from the bottom of my electric water heater.

Now, however, I'm thinking of installing a small (5KW) tankless water heater at the kitchen sink. The sink is far from the main water heater, and the line runs through a cold crawl space, so we waste a lot of hot water just heating up the line before hot water comes out of the faucet. What I'm worried about is calcium scale. The passages in a tankless heater are small. I suspect there's not much room for scale to build up before there's trouble.

Maybe the answer is to install two water outlets, just before and just after the tankless heater, so I can regularly flush the heater with descaler solution. Is that just asking for trouble? Or maybe the simpler thing is to install a regular tank-style electric water heater, a small one, under the sink.

Comments

  • Derheatmeister
    Derheatmeister Member Posts: 1,280
    Try a Scale Transformer.. Better for the enviroment and your pocketbook.. https://www.innovativehydronics.net/
  • mattmia2
    mattmia2 Member Posts: 5,298
    I'm thinking small tank type water heater or a recirculation pump with a timer started with a button.
  • Ironman
    Ironman Member Posts: 6,862
    They make valve kits for tankless water heaters for descaling.

    You'll also need a pony pump, hoses, a 5 gallon bucket and cleaning solution.

    Personally, I wouldn’t put a tankless on a system with hard water - you’re gonna have a lot of issues down the road.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,519
    Hi, I’d go for the small tank under the sink. Its less upkeep and can run on 120 volts. I like to make this tank three times the volume of the water in the hot line so the temperature doesn’t drop too much during use.
    Yours, Larry
  • captainco
    captainco Member Posts: 576
    Magnet conditioners are usually only effective at a single flow. There is an electronic device called a Clearwave that wraps around the water line and and plugs into any outlet. When I sold the old tankless water heaters in the 90's scale was a problem. Once the Clearwave was installed they never needed cleaning again. One unit can treat the whole house if you just put it on the cold water line at the meter. The only time you need to mount it at a specific device is if it is not used regularly.
  • Derheatmeister
    Derheatmeister Member Posts: 1,280
    edited November 2021
    captainco said:

    Magnet conditioners are usually only effective at a single flow. There is an electronic device called a Clearwave that wraps around the water line and and plugs into any outlet. When I sold the old tankless water heaters in the 90's scale was a problem. Once the Clearwave was installed they never needed cleaning again. One unit can treat the whole house if you just put it on the cold water line at the meter. The only time you need to mount it at a specific device is if it is not used regularly.


    @captainco
    These Scale Transformers do not use a power source such as the Cleanwave...
    Just specially oriented Super Strong Rare earth Magnets..
    As you may know the molecule structure of the Calcium is Changed in such a way that it will not allow it to deposit on anything including it's self.
    The Calcium is still present but stays suspended hence the wording "Scale Transformer"
    The Calcium will remain this way until you heat it to back up to 160 F...
    Most of our domestic hot water systems operate way below 160F
    Not only does this protect our equipment,we use less soap and have the Greenest lawn in the neighborhood by just using water without any Chemicals/fertillizers.. :)
  • csigona
    csigona Member Posts: 6
    Thank you all. I find the concept of using magnets, whether earth magnets or electromagnets, to prevent scale difficult to believe, but the hearsay is nonetheless overwhelming. I managed to find one of the Clearwave variety on eBay for only $50, not much to lose, so I'll give it a try. I'll start by connecting it to a single sink line, not the tankless heater, until I'm convinced. We'll see. I'll let you folks know what my experience is.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,519
    Hi @csigona and thanks for letting us know. Years ago the National Association of Corrosion Engineers did a small study of non-chemical water treatment devices and at that time found almost no effect. I'd like to see a much bigger study done under all sorts of water conditions so we could reliably understand where they work best. Clearly, they do work at times, but the rhyme and reason of why don't seem to be understood.

    Yours, Larry
  • csigona
    csigona Member Posts: 6
    Here's an initial report. I cannot yet say how the Clearwave device works for scale, but I can say that there's a definite difference in how soap acts. Before the Clearwave, bath water would have scummy stuff at the top and leave a ring in the bathtub. If you had let the water sit for a while, you would see how it separates into layers, where there's almost clear water beneath a layer of scummy stuff. After installing Clearwave, the dirt remains mixed in with the water. There's no more layering. The water remains cloudy all the way to the bottom, no scummy layer, no bathtub ring. It's behaving like soft water, at least as far as soap is concerned.

    So the device is clearly doing something. We have yet to see whether it's any good at preventing scale from hard water, or even, as the literature claims, slowly removing existing scale. Those will be longer running tests. I'll tell you more as I find out more.
  • hot_rod
    hot_rod Member Posts: 16,132
    A phosphate doser is another option. It does not remove the scaling minerals like an ion exchange softner but keeps the minerals locked up, in suspension so they do not coat out the surfaces of the heat exchanger.
    I've heard some of the tankless manufacturers are starting to offer these.
    We build them for the International market, but they may need to be sized up for the IUS market. Both pipe size and cartridge capacity.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Derheatmeister
    Derheatmeister Member Posts: 1,280
    hot_rod said:

    A phosphate doser is another option. It does not remove the scaling minerals like an ion exchange softner but keeps the minerals locked up, in suspension so they do not coat out the surfaces of the heat exchanger.
    I've heard some of the tankless manufacturers are starting to offer these.
    We build them for the International market, but they may need to be sized up for the IUS market. Both pipe size and cartridge capacity.

    For enviromental reasons most Europeans try not to use any phosphates Starting with the Laundry Detergents.
    IMO I am not so sure if this is a great seller in the EU and certainly would not install one for any of my customers.. :#
  • hot_rod
    hot_rod Member Posts: 16,132
    Have a lab do a good analysis to find the best options

    There are phosphates, polyphosphates, and orthophosohates, all used for different reasons and results, only a water pro would know what is needed.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Derheatmeister
    Derheatmeister Member Posts: 1,280
    hot_rod said:

    Have a lab do a good analysis to find the best options

    There are phosphates, polyphosphates, and orthophosohates, all used for different reasons and results, only a water pro would know what is needed.

    The doser you mentioned is for Phosphates ??