Limescale build up

I am starting on my hot tub project and installing my woodburning stove in a cabin ,a hot water system and storage of it is being puzzled out and the theme here is based on the KISS principle, but heres my next problem that will happen , as i am on borehole water with a high calcium content ---any water heating devise quickly builds up limescale---how or what has anyone else done to prevent this on their system ---my own current thinking is to make the heating tubes of the hottub stove somehow partially pull apart--so i can rod them out. I have just installed an electric heated pumped shower and an  in line combimate system in a modern house --this uses  phosphate ball /pellets over which the in coming cold water flows---this prevents the limescale coating the pipes and heater cores ---does not remove the lime ---it just gets passed through the system----maybe this could work on the woodstove back boiler ?

Yes its going to be a huge problem if you use ground water.  You can clean out chemically with vinegar or a product like CLR (phosphoric  acid I think).  Mechanical means are going to result in bent metal and leaks.  The real answer is distilled water - that stuff that falls from the sky is all distilled, no minerals.
I use the ground water as potable. Rainwater for everything else especially dish washing, showers etc.

If you don't get enough rain... water softener?

The hot tub is not potable water. It also need not be "new" water - IOW, it can be reused for a while, how long depending on how cleanly participants make themselves before soaking in the tub. Thus, it appears to me that: W/the caveat that the water cannot be actually poisonous, or irritating to most people, you can use chemicals in the water to change it's behavior. This is offered as a concept only because I'm afraid I'm not knowledgeable in this area of pool and public bath treatments, nor in the area of chemical activity in heat exchangers.

Another concept: As you know, the heat exchanger is the place most of the problem will occur. The higher the temperatures there the more lively the chemical activity will be. Thus, keeping temperatures a low as possible in the heat exchanger may give the longest run time between maintenance. If you want water in the tub to be 115F, then limiting exchanger temperatures to 120F will greatly reduce chemical activity compared with running the exchanger at 140-160F to mix the tub temps quickly. But that may not be possible for you. The trade-off is, of course, that it will take a long time to heat the tub initially and you will want to insulate it and all plumbing as well as possible.

However, since wood burns hot and you probably want this hot water to be on demand, you might consider an indirect system to allow you more BTU input from your wood boiler. A two stage heater, where special fluid (distilled water or some other favorable concoction - consult the manufacturer and the pros) can be run in the boiler and the heat exchange can be  done in a coil-in domesticate hot water tank. The boiler temperatures can be higher and it's heat exchanger can live in its own little sealed world. The storage tank which is where the tub water would be heated _might_ be a lot easier/cheaper to maintain.

This seems like a problem worth running by a _good_, experienced hydronic heating professional. Unless you just want to light a fire under the tub, which could work for a while, I guess, but the tub would likely have a short life. The wheel _has_ been invented before and a good pro (and you might need to talk with many before you find a likely fit) knows what concepts, equipment and techniques apply and how to balance your design goals with safety; they also can offer you workable alternatives. I haven't visited for several years so the place could have changed some, but "heatinghelp.com" used to host a small group of such people who willingly provided advice at all levels; IIRC there were one or two who installed wood systems, but it was not common.

Depending on the system you use, you could create several kinds of dangerous risks. Please take this seriously, as you are potentially dealing with a complex high temperature, high pressure system. As I understand it (I was a plumber, not a hydronic guy) wood burns hot and it's relatively hard to regulate, so safety is a very important part of the design - when something doesn't work just perfectly, you don't want to turn a storage tank into a bomb or split a little connecting pipe and spray around 300F heating fluid.

Regards
Rufus

thanks, for some input , and some pointers , the tub wont be an on demand hot water and there wont be any sealed off un-vented boiler---the idea was at first to use rainwater  only ---but the extra time needed to sort it out into a running system right now would put my main project way behind all the previous missed deadlines---the heat exchange idea with rainwater  could be put in place---its just that to use rainwater at the moment would require collecting all the bits together and still building sand filter and gravity feed tower , and so on .......

We have spring water that comes out of limestone and actually found that putting a ring of magnets around the pipe significantly reduced our timescale. Not sure why since the science behind it still doesn't make sense to me but it actually does seem to help. We also flush our on demand water heater periodically with vinegar, a couple times a year.

Hi Tony..... we have been heating well water with high calcium water in our wood stove for our outdoor hot tub bathes and showers..... using magnets DOES work... it somehow aligns the water molecules..... so that it does NOT build up as scale on your hot water pipes..... look up... (google),  magnets to remove calcium scale..... there are several companies selling them.... they work throughout your whole system, for many years if placed where the water enters your house.... it is easy... don't make it anymore complicated than necessary....   Sunny

thanks , iam going to try the magnets as well ----but diy style ---have read about their use and many say it wont work and a few say from their experience it has never worked ---but i recon its worth trying---i have about 10 magnets from old starter motor s --the linear reduction gear types---they are curved and will fit around a  3/4 copper pipe quite nicely --plus another 8 circular magnets from a microwaves --they have a center hole about 3/4 inch --so i will combine them and install it as a removable unit --- seems to me there is also a lot of mis understanding about them and other systems to prevent limescale---many are arguing about it not reducing water softness---thats not what these do .

I have read that the neodymium magnets are the most effective at reducing scale buildup. Somehow keeps the minerals from precipitating out.