Condensing Boiler with Stainless Steel Heat Exchanger and Hard Water

Hodsonian

Hi, I'm considering installing a new combi condensing boiler (HTP). One of my concerns is that I live in an are with hard water 8 grains. Is this enough to cause a problem? I would like to avoid using a salt based water softener. What is the best salt-free option?
Thanks!

hot_rod

For the boiler water itself, the manufacturers are all over the board on acceptable hardness levels. Some require "below 7 GPG'
others "less than 12 GPG" "5-15 from another"

TDS is another component to watch in addition to hardness, it's the conductivity of the water due to all the minerals in the water. The range is crazy from manufacturers from 256- 2000 PPM!

7-10 GPG is considered hard 10.5 and above very hard.

The same with ph and chloride levels a very wide range from the major boiler manufacturers.

Makes it tough to get a handle on what a contractor and homeowner needs to do to maintain boiler warranty from brand to brand, sigh!

Water that has been demineralized by any number of process is best for fill water.

On the potable water side you will see a similar range of fluid quality requirements. Minerals will coat and scale tanks, elements, heat exchangers and even tankless type DHW heaters.

Softening will help eliminate scaling and mineral build up in DHW, some folks insist on softening, others will not have it and deal with the consequences.

Look at the manufacturers requirements, from their warrant view, but take it with a grain of salt, pun intended

Jamie Hall

Whatever, the best bet is deminierlized water, such as by reverse osmosis. Fortunately, you only need to fill the system once. Whatever you do, though, do not use water softened by the usual ion exchange, salt regenerted water softeners. It might reduce scaling in the boiler a little (although that shouldn't be a problem at your levels) but it surely will accelerate corrosion, which you don't want.

Hodsonian

OK. So couldn't hurt unless I were to use a salt based ion exchange water softener. (The combi unit I bought has a stainless steel heat exchanger if that make any difference). All CH would be brand new.

I would still like to "demineralize" the water to extend the life of the combi. As far as non salt water conditioners go which is most effective for my application? I'm leaning towards a TAC based system using the polymer beads. This system apparently "crystalizes" the carbonate on the microscopic scale which prevents in from adhering to surfaces.

I'm wondering how effective this is, especially at higher temperatures in the heat exchanger and CH loop, i.e. are the benefits of scale prevention negated once heated above a certain temp?

Hodsonian

My research into RO seems to indicate that it is inefficient at removing minerals because they quickly clog the membrane. Is this more relevant with much higher hardness?

hot_rod

Here is a good read on water quality for hydronics.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_18_na.pdf


All types of water treatment have pros and cons.

With RO, chlorine content, iron levels, capacity all need to be considered. The membrane can be compromised quickly by certain water conditions.

In some cases it takes a few treatment steps to get ideal water.

We feel demineralizing is one of the best options for boiler water. It is a single pass thru a multi resin bead, no brine back washing.
De-mineralizing take away everything that a softer does, plus all the other minerals.

But you need more info on what exactly you water has in it. At the very least hardness, TDS, and ph.

Hodsonian

Thanks for the link I'll give it a read. I'm on well water (So no chlorine ect.)had it tested at (unfortunately didn't get TDS):
-no iron
-PH 7.5
-8 grains hardness
-I know I will definitely be using a sediment filter

From googling quickly looks a demineralizing filter works by RO? Is the multi resin bead different than RO? If possible could you please suggest a brand so I could see what you mean?

Hodsonian

Just read the part of the article regarding demineralization. Makes more sense now.

Rich_49

http://mechanical-hub.com/sites/plumbing/2017/01/18/eniro-water-products-pro-combo-system/

hot_rod

That water is not all that bad for potable. I hear stories of 60 GPG water in parts of the US and Canada. If you are use to soft water it will not be acceptable, of course.

I would make it better for the boiler, TDS would be the number to know. Within the TDS total dissolved solids number would be any chlorides. The chloride levels are of most concern to stainless steel boilers and tanks, most manufacturers show low acceptable levels.

A TDS meter will not indicate what is in the water, but regardless the TDS needs to be in that 100- 150 or less range. We suggest filling systems with 30 TDS. Ph will rise as the water contacts the metals in the system as RO and DI water tends to lower ph into the 6's.

Here are 3 common SS boilers brands, notice the wide range of fluid conditions from brand to brand.

uS/cm is microseimens per milligram, convert with an online chart or a 1.56 multiplier to get ppm, some meters will read either or.

I think the Lochinvar one meant to say chloride, not chlorine.

The Germans, as usual, seem to have done the most amount of boiler water quality analysis. Find this VDI standard online. I understand inspectors look at boiler water quality in Germany, as they do combustion analysis.

Be great if all the boiler manufacturers referred to this 2035 standard to establish their recommendations

JUGHNE

Water quality issues are obviously becoming really confusing.

Some suggest RO water. The story that I have been told is not to use RO with any piping other than some form of plastic, completely non-metallic. There are only a few systems around here in the country with well water that make you hold your nose. All of those I have seen use the plastic tubing. The urban legend is that RO water seeks out metals to eventually consume.

HO here installed his own RO system and later told me that his use of 1/4" soft copper was a mistake. The finished product was taking on a copper taste and he was going to replace it with plastic tubing.
Before he installed it he was saying he wanted no plastic in his drinking water, and he was one of those guys who always had a better idea.

So if the Germans have boiler water police, that must have introduced another business opportunity. Some company with a delivery tank truck of the right quality of water. Separate tank for glycol mix. Not a really far fetched plan for the future?

hot_rod

JUGHNE said:

Water quality issues are obviously becoming really confusing.

Some suggest RO water. The story that I have been told is not to use RO with any piping other than some form of plastic, completely non-metallic. There are only a few systems around here in the country with well water that make you hold your nose. All of those I have seen use the plastic tubing. The urban legend is that RO water seeks out metals to eventually consume.

HO here installed his own RO system and later told me that his use of 1/4" soft copper was a mistake. The finished product was taking on a copper taste and he was going to replace it with plastic tubing.
Before he installed it he was saying he wanted no plastic in his drinking water, and he was one of those guys who always had a better idea.

So if the Germans have boiler water police, that must have introduced another business opportunity. Some company with a delivery tank truck of the right quality of water. Separate tank for glycol mix. Not a really far fetched plan for the future?

True about purified DI or RO water that it will have a low Ph, maybe in the 6's.

In a closed loop system like hydronics that aggressive water will pull some from the metals from the system and within days seek a neutral Ph in the 7's. We have documented this in several systems around our office. The Ph will buffer itself up after that happens.

If it is a concern a small Ph boost inhibitor could be added, better yet a hydronic conditioner to give you Ph buffer, film provider, and O2 scavenger.

Now in a potable water system that sees a continuous flow of RO or DI water, the low ph will go after the metals, and pure water needs to be in plastic or composite components.

Here are some of the chemicals available for cleaning, protecting or boosting systems.

Jamie Hall

All quite true -- pure water (and distilled is the purest, DI and RO not far behind) is one of the most universal solvents known to man. Many -- but not all -- plastics are pretty resistant. No metals are.

Which is why I have heard to say, from time to time, that unless you have really wacky water quality, if you are putting it into a closed system (no or minimal makeup) there isn't that much problem. True, some scale will form initially, and true, some corrosion will occur initially. However, if there is little or no makeup, that will stabilise remarkably quickly. One might wonder why steam systems aren't more affected, since they draw in air as they cool -- but most of that air goes right back out on the next cycle, and doesn't get a chance to be a problem. And, of course, on both a steam and a hot water system in theory you don't get any new water to speak of.

hot_rod

Jamie Hall said:

All quite true -- pure water (and distilled is the purest, DI and RO not far behind) is one of the most universal solvents known to man. Many -- but not all -- plastics are pretty resistant. No metals are.

Which is why I have heard to say, from time to time, that unless you have really wacky water quality, if you are putting it into a closed system (no or minimal makeup) there isn't that much problem. True, some scale will form initially, and true, some corrosion will occur initially. However, if there is little or no makeup, that will stabilise remarkably quickly. One might wonder why steam systems aren't more affected, since they draw in air as they cool -- but most of that air goes right back out on the next cycle, and doesn't get a chance to be a problem. And, of course, on both a steam and a hot water system in theory you don't get any new water to speak of.

The scaling minerals cause the scale formation and even 1mm of scale will cause hot spots and potential failure points. 1mm of scale also increases fuel consumption 2% the experts say. A hard water, or high TDS fill guarantees some scale formation right out the gate.
High surface temperatures in modern boilers with tiny combustion chambers and intense blue flame burners make scaling more of a concern. Thin gauge metals used in modern high efficiency boilers are less able to cope with that compared to 1/4" thick cast, of days past.

Ph monitoring is one key, a change in ph has a huge influence in scale formation, a one point change say 7- 8 ph has a tenfold increase, ph is a logarithmic scale.

Corrosion in another issue and it is driven more by dissolved gasses in the system , CO2 and O2, O2 being the most aggressive.
Steam boilers often fault the waterline due to that corrosion mechanism. A higher alkalinity in steam boilers offers some scaling to help protect against that waterline corrosion, steam boilers generally prefer a slightly higher ph.

It is more important than ever with new, thin metal boilers to pay attention to scaling, including the initial fill water, and a deaerating device, like a micro bubble air purger to minimize the air, O2 and other gasses in the system to prevent potential corrosion.

A key component, getting more attention in hydronic chemical treatments is the O2 scavenger component. Newer and better scavengers in the organic based types are being used in addition to the older technology sodium sulphites. 8ppm of sodium sulphite can handle 1 ppm dissolved O2, so they need to be constantly monitored and reboosted, knowing that O2 gets into modern hydronics. Especially hydronic systems with PE tubing.

Phosphates are added to keep the scaling minerals in dissolved form to reduce scaling.

It is a challenge to think you can fill and forget modern boilers knowing all the different components mother nature can throw at it. Part of the change is due to the chemicals added, or the salts making their way into all our water sources. Some of the treatment chemical required to make "city water" safe to consume may in fact be working against you, and your boiler.

Jamie Hall

Always used to add a variety of treatments to power boilers -- the lab. I once ran had several power boilers we monitored. Daily. Was a good chunk of our income!

I expect that @hot rod is perfectly right -- he usually is! But it does make one wonder a little bit, once again, about the tradeoffs in costs between the new high efficiency units and the older cast iron ones...

hot_rod

Jamie Hall said:

Always used to add a variety of treatments to power boilers -- the lab. I once ran had several power boilers we monitored. Daily. Was a good chunk of our income!

I expect that @hot rod is perfectly right -- he usually is! But it does make one wonder a little bit, once again, about the tradeoffs in costs between the new high efficiency units and the older cast iron ones...

I think it is a combination of thinner metals, more exotic metals and blends, the tiny HX size, high BTU burners in small wall hung sized equipment. Add crappy water, poor air and gas removal, lack of maintenance on both sides of the HX, changing and unknown fuel quality, and you may end up with a 5- 10 year product life? It's hard to find repair parts for some of the 10 year old stuff out there, electronics especially.

Perhaps the consumers are learning to live with and accept that, seeing as appliances, vehicles, computers, tools, most everything is engineered or built with shorter life cycles or "sunset" dates.

I still have and regularly use some of my grandfathers tools! I doubt many, if any of my power or hand tools will last generations. I've lost track of how many cordless tools I have burned through in the last 30 years