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Water hammer in steam condensate return

Hello, anybody have some ideas why i would get water hammer in my condensate return at the beginning of a heating cycle.


  • clammy
    clammy Member Posts: 2,827
    Post some pictures of your boiler and it’s piping . Possibly the return is partially clogged . Has the bottom of your boiler been flushed out, occasionally the return into the boiler gets build up of crude if the installer installed a full port tee you can undo and flush out and make sure it’s not full of crude . Possibly check the pigtail on the pressuretroll It may be clogged . look at your system piping is it insulated or non insulated pipe forms more mud and rust which usually will end up in your returns or stay in your mains and cause moderate hammering . Has any maintenance been done to the system or boiler ? A real steam guy would flush your boiler and returns ,check pressuretroll and pigtail clean the gauge glass assembly ,clean burner tubes on gas and give everything a once over fire the system and evaluate the performance and suggest what improvement are needed ,main venting ,radiator vents and possible installation of flush valves on wet returns ,the list goes on always on bring steam system back to proper performance . There’s never a short cut to maintenance either it’s done or not simple as that ,just like a car and it’s maintenance but without a check engine light to remind us that it’s needs some help with steam it usually builds up till there’s issues then it maintenance time or attempts at fixing when really the key is maintenance without the first steps it’s all just bull . The real first step are set when the boiler is installed
    without and provision being made for the future of cleaning a boiler it become a real job usually with some repiping to be able to access the water side of the boiler ,again this usually done by the installer when the boiler is installed it’s also the sign of some one who has a clue not the clueless . This never done by lowest priced install this is why it’s lower priced ,professionals don’t take short cuts and charge more and get it right the first time out .
    Food for thought peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Jamie Hall
    Jamie Hall Member Posts: 20,416
    At what elevation, relative to the boiler water line, is this condensate return which hammers? Is it well below the water line -- a wet return? Is it well above the water line, thus either a steam main extension or a dry return (two pipe systems only), or... ?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 7,143
    In addition to pictures, can you tell where it happens? Is it new or did it always happen?
  • kevinA60
    kevinA60 Member Posts: 13
    It's hard to tell height of hammer. My guess is around 3 feet high. Water level I set to 26 3/4 in site glass. Boiler was replaced 2 years ago. I believe it is oversized. I was given IN6. Neighbor with same house just had IN5 installed. I have no main vents. I believe they were removed in the 1970s to accommodate 2 new risers for additional radiators in house. Those lines were done in copper and not insulated. I always had some hammer but not in return line until it was replaced when boiler was replaced. Im also aware that the risers off the header are not in best spot. Causing wet steam. Trying to take what I have paid for and make it work as best as possible. Pig tail and glass all cleaned along with boiler. I have drained and refilled many times until i got clear eater. Sometimes i use rector seal 8-way 
    EBEBRATT-Ed Member Posts: 13,097
    your return line is too close to the water line. the old boiler probably had a higher water line. the fix is probably to lower the return line
  • clammy
    clammy Member Posts: 2,827
    A issue I see aside from using only a single tapping is the reduction of the equilizer and the boiler return piping . This should be min 2 inch right back to the boiler w a full size tee instead of a elbow to flush it out ,the reduction of the equilizer and possibly a clogged return and no main venting don’t make any of the smaller issue go away it all needs some attention . If both of your mains end and drip into one wet return make sure that it’s below the boiler water line . It looks as though your wet return is 1 1/4 from my eye so there’s not a lot of room for build up of crude so I would suggest flushing it out . As a another note you should find some one capable of cutting in some tees and adding main vent and maybe possibly properly re piping the addition radiators that where done in copper and pipe them properly in steel .as for the boiler piping the use of both tappings and a properly sized header would have been in order if done correctly and a bit more thought had gone into the project and possibly experience the result would have been far better then what there and the issues resulting .
    Peace And good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 805
    If you don't have any manuals, they can be downloaded from the supplyhouse.com web site, just search on IN6 and make sure what comes up matches your boiler. This may be your boiler:


    It is interesting that for all 4 sizes covered by this manual the tapping is 2 inch, but in one place for the INV3 and another for the others.

    The steam velocity for your boiler @108000BTU/HR (IBR, not DOE) in a 2 inch pipe is around 32feet per second, which is higher than the recommended maximum of 25 fps in Dan's Lost Art book, pages 73-79. The DOE number is 144000 giving an even higher number of 43. This doesn't quite make sense to me. Perhaps, one of the more experienced guys on HH can clear this up.

    I did not see any recommendation in the manual for main sizes. Perhaps, the manufacturer considers the size of the main can be increased at the tapping. A 2-1/2" main would have a velocity of 22.4 based on IBR, 30.2 for the DOE rating. More reasonable, but still a bit higher than Dan's recommended maximum

    Again, be totally sure the numbers you use are for your make and model boiler. If it's not, I apologize for the distraction.