Adding ferrous to closed system

Gene_9

Hi Everyone,



Long time reader, first time poster ; )



I have enjoyed my closed system for 6 or 7 years. Whole house is floor radiant with O2 barrier mr. pex pipe. Closed design is achieved with a very clever heat exchanger that uses 25+ feet of double-wall copper pipe (from a heat pump, I think) to isolate the heating water from the potable. Heat is drawn from a Bradford White DHW heater with side taps for space heating. There are two Taco bronze pumps: one runs continuously, circulating water from the water heater, through the heat exchanger and back. The second pump is activated by any given thermostat and circulates the closed system water.



All has been fine until last year I connected a hydronic towel warmer/bar in the bathroom. The unit is made from enameled steel. I thought my system could handle the Fe since it's closed. In the first few months, I got a little bit of red cloudiness in a few of my flow meters, which I could live with. But recently the air valve started gumming up with dark red/brown muck and would spurt when clogged. I partially disassembled and cleaned the air valve and flushed that particular line. Now it's about a month later and we're back to the red/brown muck oozing out of the air eliminator.



I think the solution is to just remove the towel bar/warmer. But before I do that and go without the pleasure of warm, truly dry towels (everything's a little damp here in Seattle) -- is there a simple solution to this problem? Additive to the system?



Any help is much appreciated! Thanks.

Weezbo

see if Hot Rod ,

might have a solution for you.

from time to time he may part with some of his art work ...

*~//: )

icesailor

Rusty Goo:

That isn't a Stainless Steel water tank, It doesn't have a non ferric coil. It is about time for the "glass lining: in the water heater to start failing. Its been my long time experience that water heater tanks fail any time after the warranty runs out.

It was also my experience that PEX tube with an Oxygen barrier can leak air but may not show any problems unless you have cast iron or steel parts in the system. But that was my experience.

hot_rod

That's odd

usually the rusting will stop after the O2 is depleted.



Perhaps fresh air is entering the system? Makes me wonder since the air vent continues to be needed. Usually once the system is purged and heated, the air elimination is complete.



Do you have a good working central air scrubber, Spiro, Caleffi, etc? That should remove all air, dissolved and entrained air also.

Mark Eatherton

Simplest solution...

Buy an electric towel warmer.



Although the EVOH barrier will slow the flow of oxygen, it can't stop it. Depending upon how high you run your water determine the rate of oxygen diffusion.



Adding corrosion inhibitors is an excellent idea, and should be done with EVERY system, including those with no ferrous components. Plastic oxidizes too…



ME

Gene_9

Potable is clear

Hi Sailor,



Thanks for your reply. The water (potable) in the bradford is crystal clear, so I don't think there's anything funky with the liner. The crud is accumulating in the closed heating loop, which is separate from the potable.

Gene_9

Air eliminator

Hot Rod,



Thanks for the reply. I can't recall the air eliminator mfg but it's a sizeable piece of brass, has a small bleed nut at the top and when I disassembled the top of it, there was a floating plastic block in there with a wire brush type thing (sorry, homeowner knowledge).



From time to time, when I hear the heat-side pump making some noise (whooshing sound), I add a little bit of water to the system but that's maybe three of four times a year. That only seems to happen when there's a certain combination of loops running at the same time and trapped air gets worked around.

Gene_9

Shortest distance, A->B

Hi Mark,



Yes, you're so right about the electric option. It'll have to be on the next house because I already stubbed it out and I can't very well hide terminated pipe in the wall...



The water temperature is hard to say (I don't have a temp gauge on it) but the DHW runs at about 140 degrees. There's a mixing valve for the potable, to keep the temp safe at the household fixtures.



So all this has me wondering, how do ferrous systems handle corrosion? I'm thinking Fe pumps, Fe wall radiators, etc. Are they just regularly flushed?



What kind of additive do you recommend? And how do I add it to the heating loops? I don't see a place to just pour it in... ; )



Thanks very much!

Mark Eatherton

Bridging...

In a properly designed system, ferrous components go through a process called bridging. This is where the exposed surface oxidizes and give themselves a protective coating of rust. If the circulator is oversized, it keeps this protective patina from setting up on the oxidizing surfaces, and it continues to show rust in the water. Rust on the inside of a system is actually a protectant, to a degree.



The old guys (dead men) referred to the black oxides that came from these closed loop systems as "Black Gold". Keeping them from rusting in the first place makes much more sense, but chemical treatment on residential systems is rare by even todays standards, though it should be a mandatory minimum.



You have to have a positive displacement hand pump in order to induce chemicals into a system, and at that, you should isolate the expansion tank (if possible) and pump the chemicals into the system from one side, and extract the same amount of water from the other side. Simply pumping the chemicals into the closed system will send the chemicals into the expansion tank where they won't see any circulation, and won't protect the other components in the system.



Even system that are made of all metal pipes will get oxygen into them during periods of non use. Mother nature despises any imbalances in pressure, temperature and oxygen content. She wants all factors to be the same (equalibrium), and by golly WILL balance out the O2 on the outside of the pipe with the content of O2 on the inside. She will draw it through rubber gaskets and diaphragms, packing glands and the rubber seals on automatic air vents, etc.



All metal piped systems are less susceptible to these tendencies than a plastic system is, but they are ALL subject to the same potentials. If you have a micro bubble resorber on a system, and you keep the pump running 24/7, then the O2 content on the inside will be less, but there is still a continual elimination/replacement process going on. it's just not as obvious. If your system were all metal piped, and you didn't have a flow meter, you wouldn't know it was occurring. In fact, if you look at the walls of the whiteish clearish plastic tubing, you can see these oxides attaching themselves to the walls of the tubing. One major tubing manufacturer actually considered coloring their tubing black at one point in time just to hide this issue.



If you've ever seen the EVOH barrier inadvertently scratched off, you will see a LOT of oxidation at that point.



The other advantage of an electric towel warmer is that you can run it in the summer without having to fire up the heat source, although YOUR heat source would be on any way…



For this reason, I am also a big fan of electric radiant floors in bathrooms. You can still have warm floors in the middle of the summer without having to fire up a hydronic heat source. I actually use to do work for a GC that did BOTH in every bathroom. In the winter, the hdyronics kept the floors warm, but during the summer, the electric kicked in. He had some VERY happy customers :-)



As for chemical recommendations, there are numerous available. One that comes to mind is Rhomar. Maybe someone else will chime in. i know there is also Fernox,



ME

Gene_9

Keeping it simple

Mark, thanks for that extended reply! That's a lot of useful info. The bridging you describe, is part of that surface prep at the manufacturing level? Or is it 100% 'natural', that is, after installation?



The Taco pump that handles the zone circulation is 1/8 HP and there are certainly times when the towel warmer is the only zone running at the time. And that couldn't be more than 75' round trip. Does that qualify as an over-sized pump?



I'm curious, are ferrous systems common in new installs these days? Or are they avoided? I see a lot of cast iron pumps for sale, so I assume there's a need for them. And those modern wall mounted radiators are all steel, aren't they?



So, what do you think is my best course of action? Should I start with adding an additive then monitor the results? Or should I just remove the offending component (steel towel warmer) and replace it with something else (I did have an idea for a home-built copper towel rack)?



Very much appreciated!

hot_rod

this statement holds the key

"From time to time, when I hear the heat-side pump making some noise (whooshing sound), I add a little bit of water to the system but that's maybe three of four times a year. That only seems to happen when there's a certain combination of loops running at the same time and trapped air gets worked around."



I'd start looking for a leak. You should not be adding water to your system on a regular basis, or ever!



Another possibility is a large circ, pumping away from that central air purger, and towards the expansion tank can develop sub-atmospheric conditions and allow a gulp of air to be sucked into the system. Fill and purge until the system is noise free and cap off that or any air vents. Monitor pressure for leaks.



Does the pressure drop to zero on an accurate gauge when you hear that noise?



Chemicals are not a bad idea but check into a leak first and remember chemical treatments need to be checked and maintained and boosted from time to time. Also if DHW is produced via that boiler water in a tank of HX, the chemical needs to be approved for that use.



Ferrous is common in pumps, boilers, pipes, expansion tanks, manifolds and most hydronic systems have ferrous components and last decades.



Rust and corrosion to the point of causing vents to fail is a second indicator of a leak and fresh water being introduced.

Mark Eatherton

Au natural...

It is the process of oxidation.



Without actually running the hydraulic calculations, it is hard to say, but a really possibility that you are pushing more fluid through the towel warmer than is necessary.



I have built my own non ferrous warmers using copper for the tubing, and extruded aluminum for the bars. Looks good, (painted white enamel) and works great.



As for todays systems, they can have quite a bit of ferrous components within them, including the heat source, emitters piping and other components. Or not. Radiant panel (site built) systems can have NO ferrous components in them, if so designed, or they can have a mix. Point being, water conditioning in closed loop systems is critical to long term performance, and many people ignore it. It seems that anything that adds to the installed cost of the system that is not deemed as absolutely necessary gets cut out of the estimate.



In my own house, I too have a see through flow meter, and ferrous components, including a large cast iron radiators, as well as PEX and steel panel radiators. After about 5 years of operation, I couldn't see the flow indicator in my flow meter. I pulled the system down, cleaned up the meter, flushed the system and added a gallon (my system is fairly small) of corrosion inhibitors and my system fluid is still pristine today. I think you'd be safe just adding a corrosion inhibitor and then watching your pH (keep it between 7 and 8.5) and buffer with inhibitors as needed.



Although remote, there is also the possibility that you might have a leak in your heating system. Easiest way to eliminate that as a possibility is to shut off the make up and monitor the pressure. If it drops significantly, you need to do more investigation.



And you're welcome. Buy a book and support the site :-) They are ALL fun to read.



ME

Gene_9

Proper air eliminator use

Mark, Rod - both helpful posts. Thank you.



Oh Lord, if I have a leak that would be a nightmare. There's something like 2000' of pex line snaking around the floors of this house. I wouldn't even know where to start if I located an obvious drop in pressure. When the heating season comes to a close (May in Seattle) I guess I could pressure test (with air) each line to determine.



I don't have a pressure gauge on my system. What's a good guideline for it's placement? And what's an appropriate pressure for the system?



Also, from your comments it occurs to me that maybe I'm not using the air eliminator correctly. I never received any instruction on it so I just assumed it should always be left open, just a little. But should it be completely closed once I feel satisfied that all the bubbles are purged? If it's left open (as I've been doing) would that allow O2 in on a regular basis?



And thanks for the book buy tip! I'll have a look and take that advice.



I know homeowners can be such a pain, so thank you. I've made several calls to local guys on this issue and the responses I've received aren't confidence-inspiring. FWIW, it's my experience in nearly every trade that most contractors know just enough to get by (present company on Heating Help exempt) but not enough to competently troubleshoot. And the ones who are really good? Only the affluent can afford them. But then again, Seattle is an over-educated city where every fourth person can either write code or has a master's degree but there's too few tradespeople.  >sigh

Jean-David Beyer

. But should it be completely closed once I feel satisfied that all the bubbles are purged?

I am a homeowner, not a heating professional.



My heating system has two zones: one is radiant in a slab at grade. The other is baseboard upstairs. Originally, there were coin vents in the upstairs zone, but when I did my system over a few years ago, I had my former heating contractor replace some 3-foot long baseboard units with 14-foot long ones, and he removed those vents. He said they were not needed.



Now I have a fancy microbubble resorber (not an air scoop), that has a vent (of course) that can be closed off, but I do not turn it off. There are reasons to turn them off, and there are reasons to leave them open, so you may be told both from one contractor to another.



If your circulator(s) do not pump away from the expansion tank, and if your system pressure is a little too low, you may pull air into your system if you leave the automatic vents open. Hence the recommendation to close them.



But if your system pumps away from the expansion tank, and your system pressure is correct (about 5psi above what you calculate to get the water to the top of the system), you should be able to leave the vent open



If the system is really old, it is possible that the seat of the vent valve would deteriorate or leak because of dirt in there. For me, this is not a problem because even if it leaked, it would just dribble a bit of water onto my garage concrete floor. But if it is upstairs somewhere in your house, or worse, in a wall (very bad), you would have serious trouble.

Gene_9

Pumping away or to

Hi Jean-David,



Thanks for your reply. I'm not quite sure if my system is pumping away from the expansion tank or not. In the photo I attached to my original post, you can see the expansion tank with the air eliminator installed above it. The components in the photo are on grade, in a garage, at one end of the house. It pumps to the rest of the house on grade (about 750 square feet) and on the second story (another 900 square feet). Do you think that qualifies as 'pumping away'?



Also, I have no idea what my system pressure is (or how to calculate what it should be), so if it's too low and what you say is accurate, it might be drawing air via the eliminator (which I've been leaving open continuously).



I'd be curious what the pros here have to say on the proper function of the eliminator, but I might try this: purge the cruddy water out > refill > allow air to escape > close the air eliminator completely > come back in a couple weeks and assess.

Mark Eatherton

Pumping away and other cool ideas...

Great title for a book , eh… Oh Dang, it's already taken. :-)



You will have to trace out the piping, and the pumps usually have an arrow on them indicating their direction of flow.



All pumps work much better when they are pumping away from the expansion tank.



Fill pressure is generally at 12 to 15 PSI. You need to go to the hardware store and get a pressure gauge, and hook it up to one of the drain cocks on the heating side of the system to monitor these pressures.



For others reading this thread, fill pressure is a function of system height. You fill the system at a rate of 1/2 PSI per vertical foot of SYSTEM elevation above the expansion tank/fill valve combo, then add 5 PSI to that total. In your case, 12 PSI ought to do just fine.



When you get the gauge, make certain it has a female fitting to allow you to connect it to a male hose bib.



ME

Gene_9

proper use of air eliminator

Hi Mark - again, such useful info. Thanks.



Could you quickly comment on my earlier query about whether the air eliminator should be left open continuously or closed fully once it appears all the air has escaped? And if it's left open continuously, could that allow O2 to enter the system and cause corrosion problems?



I've attached an enhanced photo with arrows indicating the direction of the closed system flow. The red arrows indicate the flow as it leaves the heat exchanger, out to the household zones; the yellow arrows indicates the flow as returns to the heat exchanger. Seems to be pumping 'away' from the expansion tank, yes?

Mark Eatherton

Hard to say from the photos...

I can tell you this. The expansion tank in the photo, if it is in fact serving the closed loop part of the system is rated for highly oxygenated water. And that is fine, regardless of the application (closed versus open loop), but it may indicate that your system contains non barrier tubing. Treat accordingly.



As it pertains to the pump and the expansion tank, the pump SHOULD be as close to the expansion tank as possible,and it SHOULD be pumping away from the expansion tank towards the highest pressure drop components (heat exchanger and loops).



If in fact it is set up that way, then it is perfectly acceptable to leave the air vent loose so it can do its job. I know some people here will tell you otherwise, and in a perfect world (all metal pipes) you COULD close the vent after the systems is completely air free, but if your tubing is not oxygen barrier tubing, then it is continuously replenishing its air supply, and the vent should remain loose.



The double wall helix heat exchanger is double augmented, meaning the inside of the pipe is knerled to cause the water to be violent and turbulent, and that creates a high pressure drop on flow, which if the pump is improperly placed in relation to the expansion tank, it can create a rare condition that could suck air into the system if the static pressure is too low.



If you could schematically draw out how the system is actually piped, it would be better than trying to look at the photos. Something as simple as a one line diagram would be fine.



Be sure and label the components if you would/could.



ME