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Radiator "Panting"

Hello All,

I've searched the boards, but haven't been able to find anything addressing the specific situation I believe I have. If I've missed it, please feel free to point me in the right direction.

Background: I have a single pipe steam heating system with an approximately 4-5 year old gas fired boiler. I purchased the house this past January and have done quite a bit to the old steam system since including insulating all the pipes in the basement and changing out all the radiator and main vents to various Gorton sized vents. The system works much much better than when I moved in, with the entire house heating quietly and evenly, but the solution to one problem still escapes me.

The Problem: A cast iron radiator on the 2nd floor rapidly blows air in and out while it is heating up. It sounds like it's panting, or hyperventilating, with several in/out air exchanges occurring per second. (definitely not water hammer) The radiator still gets hot and heats the room, but the noise is usually enough to wake us up when the boiler kicks on at night. (its in a bedroom near the bed) This is the only radiator in the house with this issue, so I believe it is something with this specific radiator or riser and not the system or boiler. I have exchanged the vent with another from a radiator not having this issue, with the same result on this radiator.

My Thoughts:

- The boiler is oversized, and could be overfired, but wouldn't that affect all radiators, or at least the ones closer to the boiler? This is not the closest radiator to the boiler.

- The pipes are insulated everywhere they are visible, but this riser does run up along the outside wall. So if it is uninsulated in there, that could cause the panting from what I have read on this wall. However the radiator in the next room over is configured in the exact same manner, on the same main loop running up the same side of the house, and it does not have this problem. It would be weird for one riser to cause such severe panting from being on the outside wall and the next one over cause absolutely none right?

- Shortly after we moved in I made the rookie mistake (absentmindedly unpacking boxes) of leaving the boiler feed water on too long (way too long) and had water running out of the radiators before I discovered what I had done. I don't remember the radiator panting before this, but that was for a short time, and before I got the system working well enough to actually get heat up to the second floor. I have checked all the pipes to make sure they are pitched correctly after all the extra weight, and none on that main were affected, and all that seemed to be off and been corrected (or rehung). So I'm running out of ideas...

- The remaining thing I can think of is a partial blockage at the radiator valve or somewhere along the riser. This radiator is on the second floor, so the valve wouldn't have been flooded (and it seems to be all the way open, best I can tell, right now) Where the rise goes off the main it goes up about a foot to above the basement wall, then runs about level for about a foot or two, then turns up into the outer wall towards the radiator. Could the flooding, or something else, have caused a partial blockage here that would cause this panting? If so, can I fix this?

Absent input from here that convinces me otherwise my next step is to detach the radiator from the riser, double-check the valve open-ness, and then try to flush the riser. I was thinking some TSP, followed by a enough water to flush anything all the way back to the boiler. Thoughts from the experts? Am I missing something? Am I going to make things worse? Am I in over my head? I had a local contractor come out and look it over and he didn't seem to have any idea what could be causing it other than a bad vent. (which I have since ruled out)

Thanks for your time. (And thanks for all the other stuff on there, this is an awesome website)


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,572
    edited September 2013
    Heavy breathing of the radiator

    Check the pitch of the horizontal pipe before it goes vertical. If there has been any subsidence of the structure, that riser may have caused the horizontal element to go into negative pitch.

    It is unlikely that there is any debris blocking the pipe because of the overfilling (which we have all allowed to happen), but if there were; it could be flushed out by applying water pressure through the vent tapping from a garden hose.

    The panting is surely from water trapped in some horizontal part of the riser.

    You could also put some quarters under the legs of the radiator to try and stretch the horizontal part up, altering it's slope.--NBC

    P S how are your main vents?

    The main vents do all the work of removing the air from the system, which the radiator vents CANNOT do. Further to that, I believe the advice on the Gorton website should not be followed willy-billy. Check your main vents, usually close to the boiler on the top of the dry returns.
  • nolamike
    nolamike Member Posts: 9
    Breathing rad

    Just read a passage in dans book that covers that exact thing. I looked back but though it but couldn't find it. As I remember it there is to much condensate or the pipe is to small for the load and it forms waves in the pipe, cutting off the steam and make it " breathe". Could also be a dip in the line . Pictures of the boiler and size helps too. Highly recommend dans book. That's what lead me here

    Good luck
  • JStar
    JStar Member Posts: 2,752


    Take the vent off. Run the boiler until the air hole starts panting. Blow into the hole as hard as you can. If the panting stops, then you've just pushed away water laying in a horizontal pipe. If it doesn't stop, I would suspect that a nearby radiator is venting TOO fast.
  • kevin_58
    kevin_58 Member Posts: 61
    panting radiator

    How is the water level in the sight glass when the boiler is running? If it is boucing allot you need to skim the boiler. I fixed a panting radiator last year, the water level was bouncing and rad was panting. After skimming it stopped.
  • Jared_2
    Jared_2 Member Posts: 8
    Thanks for the quick reply

    I'll try and double check the pitch of that short section. It's difficult to access due to it's location and all the stuff surrounding it. My level is too long to fit in there. I could probably use one of the shorter ones anyway.

    But whether the pitch, or a blockage, that is where I suspect the problem lies. Something I didn't mention before that would line up with what you are saying is that there seems to be upward pressure on that riser. It's not as noticeable when the system is cold, but as it heats up the riser end of the radiator lifts slightly. Every time I puts stuff under the legs on the other end, the riser end just seems to rise up more. However, based on what I understand, the problems I'm having don't seem to be related to the radiator pitch itself, but that may be a symptom of the level portion being pushed down. I'll try to keep adding stuff to the other end, though the legs by the riser are already off the floor. If that dosn't work, I'll go back to the flushing idea.

    Main vents are good I think. New in the Feb/Mar timeframe, Gorton #2's on each main, with two on the longer main. And yes, I read the tip on their bad sizing info. I took the time to calculate the volumes of air in the riser & radiator for each one and sized the vents based on that as near as possible. It seemed to work well, the mains vent in a couple of minutes, and the radiators all get hot at about the same time.
  • Jared_2
    Jared_2 Member Posts: 8

    I read the homeowners guide to steam, which was very helpful, but I don't remember this being in there. Lots of stuff in there though, could have missed it. He has several other books as well. I've been tempted to get them, but haven't been able to justify it yet.
  • Jared_2
    Jared_2 Member Posts: 8

    This sounds exciting. I'll try to raise the radiator a bit first but this, using a pump or dialed down compressor, will be next if that doesn't work.
  • Jared_2
    Jared_2 Member Posts: 8
    Thought about this

    The water in the sight glass is pretty steady when it's making steam. The heating contractor that came out to look at the system did not think that was the problem.
  • JStar
    JStar Member Posts: 2,752

    You will only need about 1, maybe 2 psi of pressure to do this test. The average person can produce up to 6 psi with their own lung power. The point is, it won't take much.
  • Jared_2
    Jared_2 Member Posts: 8

    I placed some scrap pieces of plywood under the legs of the radiator to raise it about an inch and half, and the problem has completely gone away. So I guess the problem was the pitch of the pipe connecting the vertical part of the riser to the main. It's amazing that such a small change can have such big results. Thanks for the help all!
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