Is our building's hydronic heating water pressure too high? What's causing this high pitch whine?
A couple weeks ago an HVAC technician came by to fix a flame rollout issue without our gas furnace, and noticed that the pressure was high at 28 PSI. Heat had been off for a few days already, so this was cold water pressure. He checked the PRV and said the max was 30PSI, but he misread, and the worn label actually shows 50PSI. Now that the furnace has been back on for a while, the pressure is around 30-36PSI depending on how cold it is outside. From what I've found online, for a three story building with a basement like ours, the recommended pressure is closer to 20PSI. Is this correct, or is our system somehow different? It's old, from the 50s, with some new parts.
Another reason why this pressure problem is bothering me, is that as it gets higher, a terribly annoying whine becomes audible in my apartment. On a spectrogram it shows up as a distinct 473Hz peak, loudest near some heaters, but audible everywhere when things are mostly quiet. It's been happening since another HVAC tech changed the bearing assembly on the furnace's heat exchanger water pump last year, but they claim the noise is normal... I live right on top of the furnace room, but I don't hear the other pump noises, just that whine coming from the pipes.
If the pressure is indeed to high, how can I adjust it? Any idea what else could be causing that awful noise?
I've attached a few photos of the various parts of the loop. Thanks in advance for any help.
Fresh water inlet pressure:
Heat exchanger loop pressure and temperature:
PRV:
Expansion tank:
This is at the inlet. Is this was adjust the pressure?
Comments
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Not necessarily. Where is the boiler located? (basement of ground floor?) and haow tall is the building? (actually how high from the boiler is the top radiator.heat emitter?
That information will determine the necessary static water pressure at the boiler.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Several things to unpack here.
First, that bearing noise you mention is NOT normal. (470 to 480 hz is about right for some types of bearing or gear noise). Hard to say what it's telling you, but it's probably asking for help.
On the pressure. What is the system pressure when the system is cold? That is a really important number, but we'd also need to know the number of floors in the building. The 25 to 26 psig pressure your gauges show is a bit higher than I'd like to see, but if this is a three or four story building it may not be out of line. What is important is how much it varies from cold to hot, as that will tell you whether you expansion tank is functioning properly.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
As an example, assuming the radiators are on the floor of the upper level, calling each level 10'
So 35' X .433= 15 psi. Add a 5 psi safety factor, 20 psi fill is adequate.
The tank, assuming it is sized properly, would have a 20 psi air charge before being connected to the system.
5, 10 even 15 psi increase as the water heats from room temperature to 180°F is not unreasonable. On a system with a properly sized 50 psi relief 35 psi is not an issue.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Boiler is in the basement. Building is 4 floors if you include the basement. Not sure of the exact height, maybe about 10m (33ft) from ground level? Basement is about 2.5m (8ft) below ground.
Pressure when cold was 28PSI as read from the exchanger loop gauge. The fill gauge was much lower, around 9PSI IIRC.
Which gauge should I be looking at to evaluate pressure? Fill (the one without the temperature) or the one on the heat exchanger loop (with temperature)?
Even if 35PSI is safe for the system, could it be lowered to 30? That would do a lot to reduce the noise.
Speaking of the noise, when the bearing assembly broke, the first tech installed it incorrectly, which was super loud, so another tech came by to adjust it. Any chance that the incorrect installation damaged the bearings and is the source of the noise? I've been trying to argue with the company that this noise is abnormal and their fault…
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what makes you believe the sound level is related to the water pressure. Do you have empirical data?
I expect the bearing is still the issue. Sound can resonate terribly in metal water pipe (domestic and hydronic) especially if attached to structure without isolation mounts.
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You might get another gauge to screw into the system somewhere to confirm the pressure.
With the system off, no pump running 20 psi at the boiler or expansion tank should be adequate.
You will need to remove that expansion tank to check the pressure. Add a valve like this for future service. Use the extra port to add a good 60 psi gauge
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Yeah I've been measuring the 473Hz peak and comparing with the pressure (the boiler room is just one flight of stairs away), and it's been consistently louder when the pressure is higher. When the furnace was recently shutdown because a flame rollout issue, the water ran cold for a couple days, and the noise was completely gone. I'm not saying it's not the bearing, but if I can mitigate it by lowering the pressure, than that's a good enough short term solution. Long term I'm still trying to get the HVAC company to admit their fault and replace the part, or maybe we'll finally replace the old inefficient system this year…
Any suggestion how I could mitigate at the source? I already oiled the bearing according to instructions, no difference.
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I'm pretty sure there's already a service valve at the tank. I'll turn off the pump and check the pressure at the boiler again, but if 20PSI when hot is expected, than the 28PSI I saw when the water was cold is already way above that.
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The bearing noise correlation isn't with pressure, it's really with temperature. Bad bearings are often noisier when heated and the clearances shrink. Of course, when the water is hot, the pressure is higher. Swap out the bad pump.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.1 -
This. But in addition, the bearing noise may also be related to the pressure difference across the pump (not the overall pressure), as I think there is some unbalanced thrust in those pumps which is related to pressure difference.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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Other than replacing pump or bearing it’s tough to mitigate resonate noise when pipe are inaccessible as it only takes one hard mount to set up the vibrations. I renovated an old home a few years ago and made the mistake of using securing a bathroom water line to framing with a copper strap. The noise made by the pipe vibrating against the framing water is quite noisy and annoying (to me).
One time the wife was away for few days, I went so far as to open up the finished wall to remove / replace the straps with plastic type. Got all but one which was buried up under 3 piece crown molding. I can still easily tell when someone’s using that shower, I use it as an early warning system that the kids are up. 😂0 -
Do you have a pump like this? It can be rebuilt, the motor replaced, or the bearing assembly. Personally I would replace it with a newer ECM one piece wet rotor style. It will have more adjustment s available and use 50% less power. It will be virtually silent.
Or lower the pressure and go that way.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Is this a copper fin tube boiler? hydrotherm, raypak, or LAARS, etc?
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I'm sure temperature also has something to do with it, because there's a noticeable jump in the noise level when the burners turn on, but there's still a correlation with pressure and noise, probably because of what @Jamie Hall mentioned.
It's almost exactly as in your first link (red one). I'm not against replacing the whole thing, especially if I can do it myself, but we're planning to upgrade the furnace in the near future, since it's inefficient and breaking down too often. So as long as the parts can be reused in a new system, without constraining us to another similar gas furnace (here gas is expensive and electricity is cheap), that would be an option. Is the flange distance the same?
Also there are two pumps, one at the boiler (noisy problematic one) and one for the building's water loop (silent, doesn't really need to be replaced). Would I need to replace both?
Otherwise do you have any instructions/guidance on how to lower the pressure? Is 20PSI at the fill valve correct?
I'm not familiar with these terms, but the heat exchanger just looks like tubing with fins.
The noisy pump is literally hanging off the pipe. But so is the second silent pump, so I'm not sure just damping would fix the issue. I think the noise comes from the bearing and resonates through the water in the pipes. Something about the temperature and pressure is amplifying the 473Hz peak, probably through more strain on the bearing and maybe closer tuned resonance.
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That 473 hz peak happens to be about 8 times per revolution for AC motor pumps (not ECMs — they're different) and is a very common bearing frequency, although it can also be from damaged vanes.
It doesn't resonate through the water — it transmits, fabulously well, through the metal piping.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England1 -
I also noticed the 8*60Hz thing, thanks for confirming. Thing is it's only been happening since they installed the new bearing assembly last year. Is it a problem with the unit (they did improperly install it the first time they came, maybe it got damaged), or actually something to be reasonably expected? They claim it's normal an refuse to do anything more.
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Yes. Exactly yes. Who ever calibrates gauges or PRVs? Not even balance or commission outfits too often? I've asked.
After gauge is calibrated in feet then pressure can be adjusted manually when water is hot. If one must have automatic water addition; then that pressure must be low enough so that safety does not blow water.
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From the pictures it looks like a copper fin tube boiler. The make and model would confirm that. If it is a copper fin tube boiler then the noise is being caused by a restricted heat exchanger on the water side and will need to be descaled. You can confirm this by shutting the gas off to the boiler with the pump running continuously. With the flame out the high pitch squeal will dissipate. Turn gas on and create another heat demand and it will start squealing again. If you let the system cool down it will take about a minute to start doing it again.
You will need to have two drawoffs on the boiler header or on the supply and return piping with ball valve to isolate isolate the boiler from system. Hopefully they have low point drains on the supply and return and you just do it from there or you need to take the wells out of the header. RBI Futera boilers have low point ball valves with hose connections for just this issue.
i have had this problem before and ran a descaling solution thru the heat exchangers to solve. or vinegar if you prefer.
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No, its not. I service a couple of systems with 40 year old pumps that're silent. They screwed something up.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.1 -
Model sticker has long since degraded away, but I'm sure copper fin tube boiler. Found a picture from last maintenance:
I could try descaling, but considering the noise only started after the bearing assembly was changed, I'm not convinced that it's the cause. Wouldn't hurt to descale though… I'd need to double check, but I'm quite sure the system already has all the valves needed to isolate the boiler loop.
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Like i said you can test that theory by shutting off the gas valve. the circulator will still stay running. With no flame the noise should dissipate. Simple test and should take no more than 15 minutes. and its on the water side of the system.
That's got to be one of the cleanest copper fin boiler heat exchangers. I work on a lot of copper fin tube boilers because we do a lot of restaurants and hotels and they never look like that. lol
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Well that photo was taken just after cleaning, so I see the tech did a good job.
And about the noise, I know it's not as loud when the boiler is off, I've already made that observation. I'll try descaling next weekend.
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