sacrificial annodes for hydronic systems?

archibald tuttle

I generally have not thought about this as an approach for heating application, partly because I stay away from aluminum in low mass boilers and had considered corrosion in a cast iron boiler not to be generaly sufficient to be of concern for preserving the boiler integrity but rather requiring flushing and maybe strainer to keep it from circulating and clogging any finer passages in the system or lodging in valves and moving parts.

It is true I service a number of boilers on well water and although they aren't of the character that have needed notable makeup water, adding zones and maintenance on systems that weren't well set up for isolation of loops to begin with can require more water replacement in bleeding and I haven't been particularly attentive to water quality in these boilers. (and i might add steam to the question given ongoing contemporaneous threads concerned with the extent of makeup water going through the steam system as a threat to the boiler over time).

I'm as lazy as the next guy if there are alternatives for circumstances that might marginally call for water monitoring and treatment and I got to wondering why there are not sacrifical annodes in the near boiler piping on hydronic systems. Seems like it would be very easy to find a bend with a 12 to 18" run of full diameter supply pipe for the given application, e.g. 1 and 1/4 or larger, with metal conduction directly to the boiler itself where a tee could be substituted for the elbow with a 3/4" thread providence to thread a sacrificial annode in.

I understand that with domestic water, it is constantly new water with air and minerals entering all the time, but is there some caution against using this in heating? Inter alia, maybe cast iron circ bodies would last a good deal longer and I could stop obsessing about whether it would be wise to use brass or stainless. If the problem were that the annode would grow so manifestly as to harm circulation, it could be that you make that leg larger than the standard piping, and or that annual or biannual inspection is appropriate.

And if the theory is generally sound is there any further application of the theory that suggests location in the feed or supply or leaves that to convenience.

thanks,

brian

hot_rod

I wonder that the breakdown or sludge from the rods dissolving would cause more problems? With a tank water heater that breakdown residue, along with scaling mineral precipitation tends to stay at the bottom out of harms way.
I feel if you start with a cleaned system, fill with good, low TDS low hardness water, then add a conditioner and check every few years, you should have a long lasting hydronic system.

Here is an example of how the Rhomar conditioner puts a small protective film inside the piping and components. Just a few micron layer to protect the metals without hampering heat transfer. Some of the coating came off when I used the portaband saw to cut it open. This was a 10 year old Lochinvar with a Gianomi coil heat exchanger.

Larry Weingarten

Hi, I agree with @hot_rod , putting a sacrificial anode into the system could cause other problems with the corrosion byproduct from the anode/s. A way around that would be to use powered, or impressed current anodes. Still I think of the way an anode works like a light bulb. If the anode you installed were a light, where would the light shine? My picture of it is that wherever the light hits is protected. The ideal anode in a water heater would be a ball in the middle of a spherical tank. That way all surfaces would have the same protection. In piping, don't expect much if any protection past the first bend. Anything "in shadow" won't reliably be protected.

Yours, Larry

Solid_Fuel_Man

Closed system, almost complete lack of oxygen....poor electrolyte. That's why we dont see electrolytic corrosion in systems with direct connection of copper to iron which is very common to hydronics in the past 60 years. Many systems 60 years old with no corrosion. 

Water heater is a totally open system with plenty of makeup water, cannot use iron anyway. 

Just avoid aluminum. It's been proven to not work long term. The water side fairs well, so again its not an electrolytic issue. Boiler HX made of aluminum fail on the fire side because aluminum doesnt fair well in acidic environments. 

It's been my opinion that aluminum should be avoided in hydronic systems. Any coatings they add to it eventually flake off, and it all turns to white powder. 

That said aluminum is a fantastic material for lots of other applications. It holds up very well in open to the atmosphere environments, think aircraft. Windows, doors, roofing, automotive radiators, etc. I've installed many miles of aluminum wire, and utilities have used aluminum conductors pretty much exclusively since the 1960s, with no corrosion issues. 

archibald tuttle

Solid_Fuel_Man said:

Closed system, almost complete lack of oxygen....poor electrolyte. That's why we dont see electrolytic corrosion in systems with direct connection of copper to iron which is very common to hydronics in the past 60 years.

That is certainly the underlying premise to why annodes, dielectric union, etc. are not prevalent best practices for crossover in different metals in hydronic applications.

What seems to have changed to me from the longstanding experience of low corrosion environment is widespread adoption of plastic tubings (with even oxygen barrier tubing being a relative characterization). And i'm focused on systems that receive high level of makeup/bleeding water exchange (that might mean something is wrong that should be fixed but it does occur).

Also, the focused minimal use of iron (perhaps not as relevant in system with iron boiler but still . . . ), e.g. I'm running floor radiant that was installed before oxygen barrier was a thing, indeed before pex was a thing. The only iron in this whole sub-system was the circulator pump and man you should seen that thing after a couple years. For obvious reasons as oxygen diffusion became a know commodity and because oil boilers almost universally don't do low temps, these systems are isolated from the boiler by a repurposed DHW storage tank with heat exchanger. So I put a brass pump in after the first one failed and we the people 20 years down the pike, but would I have been smart in the first place to use sacrificial annode and might that have enabled much longer life for much less expensive cast iron pump?

ditto on some older systems with multiple pumped baseboard zones with the pumps on the returns but the PONPC downstream at the boiler, i.e. pumping towards, and old style air scoop. This is like a perfect storm for airbound loops in a three story house. Of course a better air scrubber might help but that is assuming that you could capture the air before it gets to third floor where bleeding is needed several times a year (only leading to more air). Back in the day this was handled with coin vents but even before covid, when i got a no heat call at 11 PM, it was way easier to bleed from the basement than to stomp around somebody's flat finding the vents.

And i haven't seen any solution to moving the PONPC to 6 separate return inputs for pumps (although i'm thinking about it maybe with one PRV and Backflow preventer feeding to 6 check valves. But the pressure regulating valves are themselves not extemely consistent over time and I'm unsure how well they would operate through checks. But this is a converted steamer with 3" manifolds and so I tend to deal with what is there (partly because there was a plan for replacement that lurks in the background, although the temps needed for this old uninsulated historic house which is difficult to touch on the inside or the outside don't hazard much advantage from modern condensing boiler.)

Long stories and anecdotes all having other possible solutions. I'm not proposing that annodes become as common best practice as LWCO, unheard of in hydronics 20 years ago but now ubiquitous. I'm wondering if, in theory for difficult applications or belts and suspenders work, whether they might be useful?

Solid_Fuel_Man

I dont think so. 

Just as hot rod said, the residue from the anode would be in the system and could create more problems. 

Best to simply use non ferrous materials and isolate. Stainless steel circulators are cheaper than brass generally speaking. 

hot_rod

Not many ferrous materials anymore if you use mod cons, and upgrade from the iron body "boat anchor" air purgers.
Cast pumps and expansion tanks are the two ferrous parts left. As @Solid_Fuel_Man mentioned stainless body circs, and coated or stainless expansion tanks, should take care of nonh barrier tube systems. Or maybe a plate HX if you want to keep a cast boiler..

jumper

Sacrificial metal in side stream to purge oxygen with filter to keep oxides out of system? Combine with demineraliser cartridge as well. Perhaps not for houses but for larger buildings? Payoff from better heat transfer is long term.

archibald tuttle

@jumper that's kind of what i was thinking. so if i put this on the return just before the pump and PONPC within 3 or 4 piping feet of the boiler with a strainer, would this be within @Larry Weingarten light or would the boiler which is what i'm really trying to protect be in the shadow. Of course I could move it closer to the boiler downstream of pump and PONPC.

As @Hotrod says, we're moving away from iron in the system, except these anchors we call oil boilers . . . and they cost money so i wouldn't mind adding a little protection.

On the Rhomar @Hotrod does that go in with an injection pump against pressure or open a cap and pour in before boiler filling or . . .

thanks,

brian

jumper

Re-emphasize side stream water treatment. Flow can be parallel or anti-parallel but it's important that a plugged filter/cartridge does not restrict main flow.

hot_rod

for a single system treatment, these kits work well. run the cleaner for a day, flush, refill and purge, squirt in the second can. treats about 35 gallons of system per can.

archibald tuttle

jumper said:

Re-emphasize side stream water treatment. Flow can be parallel or anti-parallel but it's important that a plugged filter/cartridge does not restrict main flow.

this was in your original and i see i set it aside. is there a thread on side flow treatment/filtering I should look to as a primer.

and what about a flow indicator for filter condition and changing the filter before it plugs?, yes thats a maintenance thing and less maintenance things is better. I totally admit I might be overthinking this but sometimes overthinking can prevent overdoing [or underdoing].

The investment I'm thinking about protecting here is the cast iron boiler. Now I have been through a rash of burnham's lately and I'm not always sure if what i'm seeing is the product of water quality and corrosion of sections or nipples or . . . vs. designs/material that can manifest a crack. Whereas I used to think of cast iron boilers as @Solid_Fuel_Man started off, lifetime units not challenged by a particularly corrosive environment given low fluid change despite temperatures and flow perturbations, but I'm a little gunshy when i see cast iron boilers only lasting as long as I expect from low mass boilers.

And in the job I'm working on I have a reliable homeowner who would check his flowmeter daily if I told him to, just like checking the site gauge on a steamer. But of course if side stream filtering keeps up with needs without affecting performance, this old dog could learn a new trick.

@Hotrod so this is existing baseboard with a bit of barrier pex for connections and new pensotti boiler. Do you run the cleaner to get at any manufacturing or installation chemistries (mostly pipe dope on my end but whatever it is that we skim on new steamers?) in this setting or just go with the treatment?

It's funny, the first 'treatment' i was introduced to came from the most instinctive mehcanical engineer i ever met, a guy who had formal education only through 6th grade but the armed services made an exception and sent him to the african dessert to fix bombers despite the fact that the didn't have the required educational credentials. When he came back he opened a service station (although he stayed in touch with aviation and flew his own cessna tail dragger) and heated his home by building his own waster oil burner system, with like an 1/8" delivery tube and supplied air from a small premanent air compressor for aeration. He gave a round steel fire tube boiler that i'm still running in an outbuilding and gave me an unlabeled quart of what he called "water mixable oil" which he said would make the internals last.

This is a floor radiant system with glycol that we only run occasionally. I haven't opened the system or added make up in more than 25 years and everything is still running. It doesn't do the annual hours so it is hard to compare it to an everyday heating system that runs 25 years but even on low use, stuff often breaks so I'm thinking he was on to something, but he died before I could ask him what the stuff actually was that he gave me. Sounds more like a hallmark movie than a HVAC story, but certainly a deadman's tales.

hot_rod

My opinion on glycol systems the fluid should be changed occasionally. It really depends on the way it was installed, clean system, mixed with DI water for example, and operating temperatures. Solar thermal systems can stagnate well above 300°F, so that fluid deteriorates quickly and needs to be changed more often. In a low temperature hydronic system I suppose the glycol could last 10, 15 years or more without the inhibitors breaking down.
From what I understand with steam, either keep alkalinity up to coat the iron surfaces a bit, or use a conditioner to protect the metals. Seems many of the failed steamers we see here fail for the same reason as hydronic boiler, lack of fluid quality.

Bottom line in my opinion, ALL piped hydronic or steam systems should be cleaned before putting them into service. then use good water, low hardness, low TDS. I go one step further and add a conditioner, cheap insurance in my mind.

motoguy128

My open 1 pipe steam system, the inside of my 115 year old pipes looks pretty good. Lots of oxygen in there for sure. I think the original boiler might have been in service until 1985, or about 80 years.

Even a partially open system seems to not corrode piping very fast. I suspect a protective layer of iron oxide forms and corrosion mostly stops at that point with only mechanical action removing the protective layer and a new one forms in a continuous manner. 400 some odd feet of piping and fittings has a lot of surface area to erode.

On the flip side I’ve seen 15 y/o pipe nipples almost pitted all the way through on a system with severe water hammer and lots of makeup. Seems if you manage oxygen with inhibitors or closed loop, or a sacrificial layer of rusty, you are in good shape.

What am I missing?

Derheatmeister

As Hot Rod Questioned:I wonder that the breakdown or sludge from the rods dissolving would cause more problems?
I can assure that improperly applying a sacrificial Anode in a Hydronic heating system will cause problems with Sludge...
We have used Sacrificial anodes in heating systems with great results.
Check Magnectic Online.de and translate into English for more information.
Richard.