Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Too Much Pitch?

djthx Member Posts: 52
I'm trying to get rid of water hammer occurring at the beginning of cycle on a 1" branch leading to a small 22.5 EDR bathroom radiator.  The 1" line branches off the 2" main at a 45* angle for about 6".  Then, after a 45* ell, it travels about 8.5'.  (The pitch is about 4" inch per 10 ft.)   It then connects to a horizontally positioned 90 ell, a close nipple, and then a vertical 90* ell, which leads to the 6" branch riser. 

I just finished replacing one of the ell's, which use to be a street ell.  The radiator is properly pitched (when I replaced the ell, there was about a tblsp of water in the radiator).  Since I replaced my boiler with a Smith GB200 with correct near boiler piping, the water hammer is now only slight.  The noise is definitely happening in the 8.5' branch.  Is the 1" too small for opposite flowing steam vs condensate?  Or might the 4" per 10' pitch be too much?  Any thoughts? 


  • jpf321
    jpf321 Member Posts: 1,568
    i think it could be both

    i think that it could be both to narrow and to angled ... LAOSH has a table or two regarding what size EDR each pipe size can support .. I know that I don't have any pipes that at smaller than 1-1/4" .. it may help if you vent the rad(s) on that line more slowly to limit the flow of condensate in the 1" pipe. and remember it's not the steam that's the problem .. it's the condensate returning ... if you can vent the rad slower, and produce a slower flow of condensate return, you may be ok ..

    also I think that the great angle may also cause condensate to flow back too quickly rather than just meandor along .. and then it backs up at either a non-angled location or a smaller diameter location ..like water trying to get out of the sink drain which is half shut.
    1-pipe Homeowner - Queens, NYC

    NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

    installed: 0-20oz/si gauge | vaporstat | hour-meter | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains

    Connected EDR load: 371 sf venting load: 2.95cfm vent capacity: 4.62cfm
    my NEW system pics | my OLD system pics
  • Venting

    From what I visualize from your description,  your pitch should be okay. It would have been better to have a larger pipe but a 1 " pipe should be able to work.

    Since the hammering occurs on start up, it  might be an idea to try a slower radiator vent and see what that does.  The steam entering the radiator, when the radiator is cold, condenses very rapidly and this results in a large amount of condensate. The rapid condensing also produces a large vacuum that more steam rushes in to fill.  Water hammer is caused by the large amount of condensate leaving the radiator colliding with the large amount of steam trying to enter the radiator.  If your use a slower vent, the steam entering the radiator initially will do so a slower pace and hopefully keep the volume of steam and condensate at a level where they won't collide in the pipe.

    - Rod
  • djthx
    djthx Member Posts: 52
    Slower Venting

    I'll try slowing down the radiator venting.  This makes sense.  II actually tried the opposite, and removed the radiator valve altogether, which resulted in louder, longer water hammer.  I'll post the results. 
This discussion has been closed.