Radiator hissing noise

Discussion in 'HVAC Heating & Cooling' started by wallygater, Dec 19, 2009.

  1. wallygater

    wallygater New Member

    Messages:
    133
    Location:
    long island
    Cast Iron radiators, built in to the wall, with steel covers on them. When I remove the cover they look like a block of black iron. They all have steam valves on one end. This is a steam heat system, Very old, from the 1940`s
    There is one in each room of the house, some big, some small. Great heat, very comfortable. What is making two of them hiss? What causes the hissing noise?
  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Steam displacing the air. It's supposed to hiss. No hiss = no heat.
  3. frenchie

    frenchie Jack of all trades

    No, it's not - it should be inaudible/quiet.

    Hissing means the valve is stuck open, usually by debris from the system, happens as they get old. They're not closing when the steam gets to the rad, letting steam escape.

    You need to replace the air valves. Those are the silver-colored disks or cones screwed into the radiator at one end. Easy job, just make sure the boiler's off when you do it.
  4. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    No, they hiss as the air is displaced from the radiator then when the steam hits the element the element closes and it should stop then and only then.
  5. frenchie

    frenchie Jack of all trades

    If you say so...

    Me, I've never heard a vent hiss (not so you'd notice, anyways), when it was working properly. Only when they've crapped out & are letting out steam, instead of closing like they're supposed to, does it get noticeable.

    I type this, btw, sitting at a desk that's right next to a steam rad. I can reach over & touch the vent without even stretching my arm out. My desk has been in this spot through the last 5 winters. I'm on steam heat, so is just about everyone I know.
  6. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,142
    Location:
    South*East
    Frenchie, I believe peter is right on this one. You must have your steam vents on a low setting that's why you don't hear them.

    John
  7. frenchie

    frenchie Jack of all trades

    Well, no, I must have them on a higher setting so the air gets out more easily, is what I'm thinking.

    There's another possible cause - that I've read about at heatinghelp, but never seen (it's always been a bad vent when I've seen it): when your system needs more vents, or the vents are undersized.

    I'm thinking you guys are used to under-vented systems, if yoou expect air to make noise like steam does on a blow-out vent later in the cycle.

    A well-tuned one-pipe system runs on, what, 2psi? 1 and a half? No way should that be audible. Air shouldn't need to be forced out of the system by the steam, it should be moving easily out of the way.


    Anyways, for the practical question of this particular case, we can settle the question pretty easily...



    Wally, when do your rads hiss? Before the rad heats up, or after the rad's warm all the way across, or both?


    .
  8. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    excessive pressure can make them a bit more noticeable, most residential systems run about 1/2 a pound but occasionally large systems or 3 floor houses need to run higher.
  9. wallygater

    wallygater New Member

    Messages:
    133
    Location:
    long island
    hissing noise

    There are eight rooms in this house and 8 radiators. We have lived here for 18years. The radiators, when working correctly, do not make any hissing noise whatsoever. Every now and then one will start to "act up". In the past I have gently taped the valve with the handle of a hammer. Sometimes this works and sometimes it don't. I have also changed out a valve or two. The problem with that is it is very hard the find the same one, and they are very expensive. The last one cost me 30 bucks.

    I have to agree that the valves are getting stuck. I have two of them right now that are hissing night and day. The hiss begins as soon as the steam starts coming up from the basement and continues to hiss until it turns off.
    The noise does not bother me at all. I just have a feeling that the radiators that are hissing are not working as efficiently as they should be. Also as you know when ore radiator is acting up on a one pipe system it potentially could be affecting all the others.

    You answered my question about what could be causing this. Debris. That seems very likely because the water in the 75 year old boiler is nothing but red rust. Its disgusting. I would imagine the steam that it is producing is also red rust flavored steam.

    I am going to try to soak one of the offending steam valves in some kind of solution. Maybe that c something r stuff, or maybe some vinegar and water.
    Maybe that will clean/free them up. I will post back with the results.
  10. frenchie

    frenchie Jack of all trades

    Steam systems rust, it's normal, because they're open to the atmosphere. You need to get the boiler cleaned every now & again, and accept that vents are meant to be replaced every now & again.

    Valves sometimes malfunction because they're dirty (but good luck cleaning them out), also sometimes because the bit of metal that springs them shut, wears out. Boil it in vinegar for a hour, if that doesn't work, replace them.


    What are they, adjustable Hoffmans? Vents normally cost about 1/2 that. At least around here they do...

    Anyways, whatever you do, don't neglect this - if you system is releasing steam, it's refilling with fresh water more often, which leads to faster rusting & more crap in the boiler, which will clog the other vents worse/faster.

    Also, depending on where in the cycle it decides it's low on water & the valve opens, it can really screw up your system's efficiency, too. Not just by cooling the boiler down in mid-cycle - if it starts filling before the condensate returns, by adding too much water. That leads to water in the pipes & rads, which then leads to pinging, blocked steam, and all sorts of irritating havoc.



    BTW, greatest source of info on steam heat, and he's out on LI, too:

    http://www.heatinghelp.com/
  11. wallygater

    wallygater New Member

    Messages:
    133
    Location:
    long island
    hissing noise

    I`m going to try that boiling with vinegar idea tomorrow. I can shut down one of the hissers with the shut off valve. They all have one.

    If that don't work I`ll have to find a place to buy them at a more seasonable place. Maybe the big orange box has them

    I have to manually fill this boiler up my self, but yes you are correct, it has needed more water, more often, than usual

    Thanks for all the great advise, I will post the results tomorrow.
  12. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    soak them in CLR

    A brand new Hoffman 40 is like 25 bucks. For something that should last a good 10 years, 25 bucks is cheap
  13. frenchie

    frenchie Jack of all trades

    Boiling in baking soda... logically, might make it worse. No reason why it would help. Acid / base, yeah?
    Last edited: Dec 22, 2009
  14. wallygater

    wallygater New Member

    Messages:
    133
    Location:
    long island
    Results

    I removed the cover and proceeded to remove the vent.
    Vent came off with no problem
    I soaked the vent in CLR for 1 hour
    Then I boiled the vent in water and vinegar for 1/2 hour
    Then I let it soak another 1/2 hour
    I then replaced the vent and turned up the steam
    This is the part that kills me, the hissing noise started coming out out the shut off valve. At the stem. I think that was where the noise was coming from all along, but like an idiot I never checked. I just assumed it was the vent, like it was the last few times.
    I purchased some graphite packing rope, took off the nut, wrapped around the stem a few times, replaced the nut. No more hiss
    Now I will never know if all that cleaning I did to the vent worked.
    I do however have one more hissing radiator to go. This one is not as bad, but tomorrow I plan to fix it. This time I will remove the cover and see exactly what is hissing first.
    On a side note; when I wrapped the graphite around the valve stem I think I must have put to much on. when I began to tighten the nut back up I noticed that the valve got very hard to turn open or closed. I made sure that it was in the open position and finished tightening up that nut. Now the valve is stuck tight in the open position. No way I could close it. I think it must be because I put to much of that graphite rope in there.
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    You probably tightened the nut too far. It's tapered inside, so the more you tighten it, the more the packing compresses around the stem.
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