Indirect HW off steam- shaking circulator

WilliamME · January 30

I just had my indirect water heater hooked up to my boiler yesterday. I noticed the circulator shakes when it runs, and I can feel turbulence in the pipes feeding the coil. There's also some knocking noises inside the tank. The zone does have an aquastat connected to a boiler tapping and that is set at 160 degrees. The water tank aquastat is set to 135, I adjusted it up from the 120 they set it at. The water level in the boiler is set higher than the tapping they used to supply the tank. There were very few supports installed, I was thinking of adding some. For the time being I placed some concrete blocks and a piece of wood under the circulator as a quick support, but it still shakes anyways. I guess I am just worried that steam is getting into the coil, but like I said the water level is good, but perhaps where steam bounces a bit in the boiler it is still getting in anyhow?

Boiler install is new, replacing an old broken down system that I posted about on here 4 years ago. Indirect tank is re-purposed from old boiler. I know there's no drop header, but I was grateful to find anyone willing to replace it at all. Here is the link to my thread from 4 years ago if you need back story.

https://forum.heatinghelp.com/discussion/181323/need-new-steam-boiler-maine

I am going to try and attach a google link to a video about how it's plumbed and a video of the shaking as well. Looking for opinions if I need to be worried, or what information I should know before contacting the installers to troubleshoot?

https://photos.app.goo.gl/xCN76jL1VN9LspaJA

ethicalpaul · January 30

If you try to pump steam boiler water directly out of the boiler, it could be at 212-215 degrees and the pump could introduce low-pressure at the supply side which could result in that water flashing to steam resulting in all kinds of havoc.

This article describes the various issues:

https://heatinghelp.com/systems-help-center/how-to-run-a-hot-water-zone-off-a-steam-boiler/

This is one of the many reasons why I think that domestic hot water is better handled by a standalone water heater.

PS: which way is the pump pumping? According to the label on the indirect tank, it seems to be pumping into the boiler. It should be pumping away from the boiler, but I can't see the indicator on the pump.

EdTheHeaterMan · January 30

The pump location is important. As low as possible. And the pump inlet as close to the boiler as possible.

WilliamME · January 30

https://forum.heatinghelp.com/discussion/comment/1839012#Comment_1839012

I checked the arrows, they appear correct. Water is flowing from the upper portion of the boiler, through the coil, into the circulator where it is pumped into the bottom of the boiler.

In terms of the 212 degree water. I thought the aquastat set at 160 would prevent boiler water hotter than that from entering the zone. I suppose it's likely it would never turn on with the steam system going. I wonder if this aquastat isn't actually wired in to the zone? I haven't looked inside the boxes to study. I did overhear a tech calling into the service department asking why he wouldn't be getting any flow when he was close to finished. Could it be the solution was to bypass the 160 degree aquastat? This is a guess, I am not sure. It could have just been they had put the circulator in backwards initially, and the Taco Flo Chek valve was preventing flow. I don't know, I'm making assumptions based on overhearing, which can often be easily misunderstood.

I understand indirect with steam is not ideal, but it did seem to work well with my previous boiler. However my previous boiler was dying and struggled to produce steam, perhaps this was advantageous for the water heater.

EBEBRATT-Ed · January 30

As others have mentioned the circulator must pump out of the boiler lower connection to the indirect inlet and then from the indirect outlet to the boiler upper tapping.

Pumping out of the boiler upper tapping will not work with the hot water will make the circulator cavitate

WilliamME · January 30

Ohh okay. I am sorry I was slow to understand what was meant. So it's all backwards. If I can't have this corrected by them, can I leave the Flo Check where it is up by the upper tapping, but just turn it around? Or does the Flo Chek need to get moved to the bottom of the boiler ahead of the circulator?

WilliamME · January 30

So the cavitation is caused by there being less static pressure on the water coming from the top of the boiler? I've been reading the link that was sent to me, and working to understand. I believe I understand what I need to ask to have repaired, but I was also interested in the science of what is causing the cavitation.

ethicalpaul · January 30

In terms of the 212 degree water. I thought the aquastat set at 160 would prevent boiler water hotter than that from entering the zone.

When the boiler is making steam, the aquastat can’t lower the water temperature.

The aquastat is there to make sure the boiler water is at least hot enough to heat the tank. It can’t cool the water down.

Ps: I don’t like indirects even on hot water boilers

WilliamME · January 30

https://forum.heatinghelp.com/discussion/comment/1839051#Comment_1839051

Yes, I can tell you don't like indirect HW on steam! That's okay!

Thank you for tolerating my plumbing ignorance. Okay, now that you explain what the aquastat is doing, that seems pretty obvious that it would still be letting water hotter than the set point pass through. I didn't think it could somehow cool the water down like perhaps a mixing valve? But I did mistakenly think it would override the water heaters call for heat if the incoming water was measured to be too hot. But it makes more sense that it wouldn't do that, because in the winter the boiler water must always be very hot.

ethicalpaul · January 30

there could be a mixing valve or bypass loop (see the article I linked you)! That would indeed moderate the water temperature

But your installer seems to be pumping directly from the boiler to the tank. But I can’t tell 100%

WilliamME · January 30

I did look at the link, I just haven't processed all the information yet, that will take me awhile, I am not a quick learner! But thank you for providing it! Heat exchangers would not be in my budget.

In terms of mixing the supply water with some water from the return side, in your link it seemed like they were referencing capturing some of the output side of a hydronic radiator to obtain cooler water from. Would that still be effective with an indirect heater where it's not subject to continuous heat loss?

However, since you've pointed it out, I believe your suspicion is correct. The circulator arrow is pointing towards the boiler. The supply side of the indirect tank is fed from the upper tapping of the boiler. I'd like to try and have them fix the flow direction for starters, and if I still have problems with it being fed direct off the boiler I may need to start thinking of investing in a more robust setup. I was mostly just hoping to get back what I had before, this tank was hooked up basically the same way to the old boiler as far as I can tell, except I am assuming they had the flow in the proper direction.

mattmia2 · January 30

May need to add the bypass that is shown in most diagrams for hot water loops off a steam boiler or a ball or globe valve on the discharge of the circulator so you can throttle it.

ethicalpaul · January 30

I did look at the link, I just haven't processed all the information yet, that will take me awhile, I am not a quick learner! But thank you for providing it! Heat exchangers would not be in my budget.

Absolutely, there's a lot in there. I definitely am not saying you need a heat exchanger, there is a lot of stuff in that article unrelated to you. But the relevant stuff is about water flashing to steam/cavitating.

regarding the mixing, you could for example mix water returning from the indirect tank with water from the boiler before it goes into the circulator. This would have the effect of cooling the hot boiler water to some safer temperature like 180-190 or whatever.

except I am assuming they had the flow in the proper direction.

Never assume 😅

I may need to start thinking of investing in a more robust setup

The setup is robust enough with the possible exception of a mixing mechanism to cool the 212 boiler water. But they should have put that in from the beginning and they should fix it for you.

Before investing in any more robustness, be sure to weigh that against the cost to buy and install an electric water heater. The sunk cost fallacy is a real thing.

hot_rod · January 30

Here are the numbers that Grundfos show for the pressure required to prevent cavitations If the boiler doesn't present that then just the water level above the pump is providing pressure on the circ. So the lower the pump the better.

Not a great application for a circulator.

Grundfos NPSH copy.png

mattmia2 · January 30

Cavitation will detroy the circulator even if you bolt the piping down. You need to fix the pressure/temp combination so that it is below the point where the water flashes to steam.

WilliamME · January 30

It is my gut opinion that I will be fortunate if I can get the company to even correct the flow direction. The boiler was installed in November sans water heater, despite the fact it was on the contract. The guys installing it have been pleasant to deal with, but management back at the office has not been great when it comes to communication and scheduling. I had to go with a big company, instead of an independent contractor so I could get financing for the install. I've spent the past 2 months essentially hounding them to come out and do the water heater, and have avoided paying the bill- so at this point I do believe it would be easier to add a bypass myself if that is what it needs. But is there any possibility my issues may disappear if they correct the direction the flow is going in? I like the idea of throttling the flow with a globe valve.

I actually have a heat pump hot water heater as well. I installed it when the boiler died 4 year ago. This indirect water heater is only serving one bathroom (primarily my wife's 50 gallon bathtub), but I have a valve I could move to have it serve the whole house if needed. I get frequent power outrages and do not like trying to operate the electric hot water heater with a portable generator, which is the main reason I wanted to retain a hot water option that was fed off the boiler.

ethicalpaul · January 30

Your situation, like so many, is complicated. Thanks for the additional info.

It sounds like maybe you haven't paid them in full yet? That is good. Surely I wouldn't pay someone for an install that wasn't working.

I don't think that just reversing the pump direction is going to solve everything. Boiling hot water will still enter the pump, and that is going to cause difficulties I think.

Just for fun, here is a link to my hot-water loop that I slapped together. It is not going to solve your problems, but it might give you some ideas about how you could put in your own bypass and it might make the ideas clearer in your mind. Good luck! (bypass loop talk starts at 8:30 into the video)

https://youtu.be/IzIO-IAIoOM

WilliamME · January 30

https://forum.heatinghelp.com/discussion/comment/1839091#Comment_1839091

Thank you! I will check out your video!

I sent my videos to the installation company today, and they were actually very responsive, they're going to send someone different out to meet me tomorrow to look at it. This thread will help prepare me for the meeting. Thank you!!

WilliamME · January 30

I watched some of the video, but I will need to re-watch some more. I want to fully understand my options when I meet with them tomorrow.

I will try and suggest to the contractor adding a bypass to cool the supply water. So, presuming for starters they proceed with reversing the flow so the supply is coming from the bottom of the boiler (this would increase the pressure on the inlet side of the circulator, thereby giving me an overall higher net water pressure despite the low pressure zone it naturally creates?), the bypass leg should come from return line of the indirect tank and be piped in just ahead of the circulator inlet, with a ball valve for metering. There is already a ball valve on the bottom of the boiler supply going to the indirect. I probably can't get them to move the circulator closer to the boiler than it already is.

What happens when you throttle incoming water to a circulator, it doesn't make it harder for the circulator to spin? I too am not very familiar with fluid dynamics.

Another strange thought popped into my head. Would it be silly to have a piping configuration that was only used in the winter, where the indirect water heater was served by gravity alone, with an electronic check valve that closed off boiler water when the inside tank temperature was satisfied? I know the recovery wouldn't be as great, but would it be terrible?

I was also wondering about priority zoning. Would it be less likely to cavitate if it wasn't trying to make steam at the same time? My boiler is 165,000 BTU, I believe it could recover my 40 gallon tank in 20 minutes if I read the manual correctly. I think I could survive 20 minutes without steam heat to let the indirect take control of the boiler for itself. Is that another good option?

Jamie Hall · January 31

Taking pumped suction from a steam boiler isn't complicated at all. But it is also not forgiving at all, and there is only one way to do it right.

The pipe from the boiler to the pump must be the same nominal size as the tapping on the boiler or the inlet diameter of the pump, which ever is larger. It must be absolutely straight for a minimum of 12 pipe diameters before the pump inlet and should not be longer than 12 pipe diameters, or if the pump can be set lower than the tapping that is permissible, but the lead to the pump must still be that diameter and straight for at least that length, and the pipe size should twice the diameter otherwise required. . If there is a valve on it, it must be a full port ball valve. The tapping on the boiler which is used must be the lowest available tapping.

Then, and only then, do you have a reasonable chance of not having at least occasional cavitation in the pump and early pump failure.

WilliamME · January 31

https://forum.heatinghelp.com/discussion/comment/1839142#Comment_1839142

Hi Jamie, I believe according to your formula my circulator inlet is too far away from the boiler, and where it elbows into the inlet it would need to be 8" of straight pipe and it is less than that.

I referred to the manual's instructions for hooking up the indirect. I will attach the screen grab. They have the circulator pumping from the top of the boiler, so in that sense the installers followed the instructions. However, they did not use the tapping on the bottom back side of the boiler, they used the front tapping on the bottom which I have circled in red. The other place they deviated from instructions was to not run the the supply piping downward first before going to the water heater, it basically goes straight across to it. Strangely, the manual says the upper rear tapping it is 1". It's actually 3/4".

I did some more tests running the water heater cold to trigger the circulator. I listened more closely this time. The majority of the cavitation sounds like its happening inside the water heater more so than the piping and the circulator. After it runs for about 5 minutes it stops making noise. Could the problem actually be the relatively cooler water inside the tank causing the boiler water in the coil to cavitate, but then once it gets uniformly warmed up, it stops? I don't have a thermostatic mixing valve for output water temperature. Do you think if I had one of those and ran a higher indirect tank temperature it would reduce cavitation as well?

hot_rod · January 31

This type cavitation is about dropping below the vapor pressure of the fluid. So temperature and pressure are involved. More on this below.

Screenshot 2025-01-31 at 8.33.30 AM.png

Screenshot 2025-01-31 at 8.33.44 AM.png

ethicalpaul · January 31

I think they bushed it down going into their copper. They should leave it full size and move the pump as low as possible, while pumping away from the boiler. And they were supposed to install a dirt screen before the circulator. And the circulator should be stainless or bronze, I can't tell but this one looks cast iron (although I admit I did use cast iron on mine, but I keep my boiler water very clean).

Their choice of return tapping doesn't bother me…the water will mix quickly in the boiler regardless of where they dump it back in.

WilliamME · January 31

Yes, the circulator is cast iron. I have a goal of keeping my water clean as well, so hoping can get away with the cast iron and no strainer for now.

You are right, they did bush it down at the front from 1 1/4" to 3/4", but wouldn't they need to do that in order to interface with a standard circulator? I've never installed a circulator, so I do not know.

As stated before however, the circulator is pumping backwards according to the advice given here, the arrow is aimed towards the bottom tapping of the boiler, the circulator is being fed from the return side of the indirect water heater. Am I mistaken, or does the instruction manual request to do it this way? In other words, is the instruction manual wrong in the opinion of those you participating in this thread? Is this common to encounter?

EBEBRATT-Ed · January 31

Turn the pump and flow check valve around and pump in the other direction.

The resistance of the flow check and the resistance of the indirect coil are starving the pump and causing cavitation.

Can't say if turning thoes two items will be a 100% fix. The suction pipe coming out of the boiler should be 1" minimum and it would be better if it was larger. All indirects should have minimum 1" pipe.

Turning those two things may get you by

The flanges on the circulator can be changed to accommodate this. Keep the circulator as close to the floor as possible.

Your installer screwed up

You always locate a circulator to push against high restriction not pull through high restriction.

WilliamME · January 31

Is it okay to ignore the supply / return labels on the tank? I.e. can just reversing the flow and check valve, but not change the piping be okay? I will see if I can encourage them to upsize the inlet size of the circulator to 1".

ethicalpaul · January 31

Lots of things can work but presumably the tank manufacturer had their reasons for specifying the flow going that way. And any installer with a little pride of workmanship would follow those specifications and all the rest. It looked like Burnham did a good job specifying how things should be in their manual.

1" pipe from boiler to circulator as direct as possible
circulator located as close to the floor as practical
Dirt screen in front of circulator
circulator pumping away from the boiler toward the tank
1" pipe to tank (I'm assuming here that the tank fittings are 1")
Bypass loop from tank outlet back to pump input with metering valve (ball valve isn't the best for this but it works)

Generally speaking you want the water to flow as easily as possible into the intake of the circulator so that cavitation/flashing is minimized. After the circulator is less critical because the pressure will be higher on that side.

Jamie Hall · January 31

The tank isn't the problem. It will be easy to repipe the thing so that the outlet of the circulator goes to the inlet of the tank.

The problem is the piping to the inlet of the circulator. It MUST come from the lowest possible tapping on the boiler, and it must have as few bends as possible in it, and it must be as large as possible.

I don't like the diagram, as it shows the inlet of the circulator supplied by the upper tapping on the boiler. However, it will work that way if there is ample water above that tapping at all times in the boiler (at least 4 inches) and if the piping is large diameter (the 1" is none too big) and if the circulator is located as close to the floor as possible.

All that said, if you simply reverse the flow through that circulator, as @EBEBRATT-Ed suggested, you may get away with it.

ethicalpaul · January 31

It MUST come from the lowest possible tapping on the boiler,

One small quibble here @Jamie Hall . I can tell you that the indirect tappings on my boiler specified by the manufacturer are not the lowest. Nor are they the highest of course.

As long as you are pulling always from below the water line and running the pipe quickly to a low point outside the boiler, I think that is what is desired. If you pull from the bottom of the boiler, you will get too much dirt maybe is the thought. Although with as violently turbulent as boiling water is, any free dirt is prone to be sucked out regardless, that's why I like to keep the dirt to near zero with my pH level (oh no not that again).

STEAM DOCTOR · January 31

Put the circulator as close to the boiler outlet as possible. And even more importantly, put the circulator as close to the floor as possible. Personally, I do not use flowchecks at all in these applications. I tell from the picture, and my apologies if this has been mentioned, but make sure the return tapping is low enough that it is constantly submerged in water. Even when the boiler water level drops due to normal operation..... 1" is a typical minimum pipe size that I try to use, and have used many times successfully.

STEAM DOCTOR · January 31

Not sure how well the "E" circulators work with your typical steam boiler, that has some degree of dirty water. Not a big fan of introducing anything that restricts flow or causes pressure drops. Including flowchecks and filters

STEAM DOCTOR · January 31

These circulators are designed to work with a certain amount of pressure. Steam boiler have close to zero pressure as it is and you would like to eliminate anything that might reduce that pressure.

ethicalpaul · January 31

https://forum.heatinghelp.com/discussion/comment/1839291#Comment_1839291

You put the filter such that even if it is restricted, the bypass loop will still provide input to the circulator. That way, the filter getting dirty only lowers the temperature of the loop instead of destroying the circulator. This is outlined in Dan's article I linked above.

WilliamME · January 31

The person who came to look at it today had not seen the job before. He wishes to re-pipe it exactly as the manual states. He wants to move the circulator closer to the upper tapping, ahead of the water heater, and have the return enter the bottom rear of the boiler, instead of the bottom front. He agreed when I suggested the flow should be in the opposite direction, but suggested his hands are tied dealing with Burnham if he has issues, if he has not first done it the way the manual specifies. I also mentioned the bypass loop, he said he has done those before and is familiar with them. Sounds likes there's a potential for this job being done up to 3 times, but we have to go in a certain order.

WilliamME · January 31

https://forum.heatinghelp.com/discussion/comment/1839297#Comment_1839297

Perhaps I can encourage them to add a strainer while they are re-piping it anyway. That is after all, depicted in the Burnham diagram.

ethicalpaul · January 31

Since I think you haven't paid them yet, if I understood your earlier statements, I would think you might be able to have some persuasion.

EdTheHeaterMan · January 31

@WilliamME … I have been following this for a while and see that you have asked if several different things can work outside of repiping the system correctly.

My first thought after looking at your pictures is to open the FlowCheck valve to the manual open position and flip the circulator pump to pump from the bottom of the boiler to the water heater return tapping. Just turn the circulator around. That is easy with the valves there. You could do that yourself. This will be positive proof in your mind that pumping away from the lowest point in the boiler WILL solve your problem.

If you find that the water heater overheats when the circulator pump is off, then you need to install the flow valve properly. That will involve some repiping. At that point you should have it done correctly.

EBEBRATT-Ed · January 31

I see no need for a flow check. All the flow check does is add a restriction. Its purpose is to prevent gravity flow. The amount of gravity flow from the top of the boiler to the bottom of the boiler is negligible.

As far as the flow through the indirect it should be as the tank mfg recommends. However reversed flow may not change the operation of the tank that much.

I would assume they would put the hotter boiler water into the lower coil tapping as you will have colder DHW at the bottom of the tank don't know if this is true.

STEAM DOCTOR · January 31

https://forum.heatinghelp.com/discussion/comment/1839297#Comment_1839297

You will not get very much heat into the indirect, if you're only flow is through the bypass loop. And just for the record, I have piped many indirect off of steam boilers, without any bypass loop.

STEAM DOCTOR · January 31

My apologies if this was mentioned. Which indirect do you have? There is a substantial difference in the pressure drops in various indirects. Doesn't really matter if you're using a hot water boiler. But make some major difference when using a steam boiler. Because, as said before, you are starting off with close to zero pressure as it is.

ethicalpaul · January 31

https://forum.heatinghelp.com/discussion/comment/1839341#Comment_1839341

thank you, I’m aware the bypass loop doesn’t provide heat. But the lack of heat should incentivize someone to check the screen.

As for the bypass loop I believe you, I’m just going by what Dan taught me. It’s nice to be on the right side of that argument lol

Indirect HW off steam- shaking circulator

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