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.

Slope for one pipe system

Mattg Member Posts: 2
I have a one pipe system with a dry return serving a two floor home. We have been in this house for 18 years and until having a new Utica Boiler installed three years ago never experienced more than occasional water hammer. When the boiler was installed we had significant surging and more noticeable water hammer which were largely resolved via skimming the boiler.

This winter we have had two leaks . The first was at a radiator valve and when the repair was completed began to notice greater water hammer problems. Just last week we had a leak in the joint near the end of the main which required replacing about 10 ' of 2inch main just upstream of the dry return. The water hammer has continued as before .

I have been skimming the boiler and notice the water is dirty although there is no surging in the gage glass. I plan to continue skimming in hopes this helps.

During the course of checking these issues I notice that the main has very little, if any slope. ( I assume the original installer did not want to compromise headroom. The return has more slope and I can hear condensate trickling back toward the boiler.

I have had two local plumbers involved but I don't have confidence that they understand the nuances of a one pipe system, counter flow versus parallel flow, etc.

I should mention that the steam piping at the new boiler is copper while all the remainder is steel. The dry return is also cooper.

I am thinking of having piping mods done after this heating season , definitely if the water hammer continues. I am looking for some guidance regarding where to focus attention .is slope the most important ( which would require changes to the main and the five or so radiator returns) or should I first look at simpler fixes such as cleaning the system.

By the way, I have replaced radiator vents and am adding some insulation on a few sections of mains and risers that are currently up insulated.


  • Jamie Hall
    Jamie Hall Member Posts: 23,443
    I can see

    at least two problems from your post.  First, all steam systems need to have slope on both the mains and the dry returns.  The best way to determine how much is to get a copy of Dan's The Lost Art of Steam Heating (available from the shop tab) and read up on the systems.  Then figure the load on each pipe, and find the correct slope -- the tables in there are comprehensive and quite simple to use.  You can also figure out whether your mains are counter flow or parallel flow -- the required slopes and sizes are different.

    One major thing to keep in mind when looking at pipe slope is the the water must be able to flow freely back to the boiler, one way or another -- no low spots or flat spots or sags anywhere.

    The other problem is the copper piping around the new boiler..  First off, never use copper pipe for steam -- particularly around the boiler (it's OK for wet returns)..  The expansion stress in the copper is a lot higher than iron, and it doesn't give the way iron does -- so something else has to; all too often, the boiler.  Second, if the installers used copper pipe the odds are very good that they also didn't do the layout of the piping properly.  This could be giving you wet steam, which can easily cause water hammer (and other problems) even when things are sloped properly.

    If you posted a few pictures of your boiler, showing all that new piping, we could comment further on it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Mattg
    Mattg Member Posts: 2
    Follow Up Info

    Thanks for your comments.

    I do have a copy of Dan's book and am familiar with the slope recommendations. Since the syetem has been "hammer free" ( with minor exceptions) for most of the 18 years we have been here , I have not done any pipe mods. When the new boiler was installed 3 years ago, I wish I had paid more attention and questioned the installer's use of copper piping.

    Since we have been having much more hammer this year I am studying the piping for upgrades and correcting the slope is at the top of the list. I will also recheck the piping sizes per Dan's recommendations.

    Attached are some photos around the boiler and also at the end of the main which is about 20 ft away in the basement. The main height at the boiler is constrained by the floor beams but I should be able to get a few inches of slope away from the boiler. I would have liked to have made this correction when we had the recent steam leak but, given the extended cold spell we have had, it would have required shutting the boiler too long so we went with just replacing the piping at the end of the main where the leak was.

    I have been skimming the boiler the last few days and still notice the water is dirtier than I would have expected. It has helped the water hammer some and I plan to do some more. My guess is the system has not been completely cleaned in many years, except for a bit when the new boiler was installed. I asked my service constractor if they routinely skim and he replied only when it's needed. Since there is no drain in the basement, the service techs usually just look at the water in the gauge glass and opt not to skim at all unless I ask. Any thoughts regarding the cleanlness of the water would be appreciated.

    From the photos you will see that the main and some of the takeoffs are not insulated. I have ordered some one inch fiberglass and will address this shortly.

    I also attached a photo that shows the return at the close nipple . The boiler recommendations call for this connection to be a minimum of 2 inches below the water level. The current location is higher than this so if I do any mods, I would look to lower this ,as well.

    Any other comments would be greatly appreciated.