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One pipe system minimum pipe diameter

Can I run a one inch line to feed a small one pipe steam radiator about 10 feet from the main?

Radiator is about 2 feet high and 2 feet long


  • FredFred Member Posts: 8,503
    Do you know the EDR of that radiator? 1" will support 25 to maybe 30 EDR if I recall correctly. I always prefer 1-1/4" pipe minimum but that's just me.
  • BobCBobC Member Posts: 5,174
    edited January 2016
    I have a 23 ft long 1" line feeding a Sunrad with an edr of 17.5. It's worked just fine for at least 35 years. The tables say it's good up to an EDR of 25.

    The slope on that line has to be good.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • oopsplumberoopsplumber Member Posts: 14
    Thanks guys

    How do I calculate edr?

    The rad 2 feet high, 2 feet long, and 9 inches deep with three columns
  • oopsplumberoopsplumber Member Posts: 14
    The slope is a 1/4 inch per foot
  • FredFred Member Posts: 8,503
    If it cloumn and not Tube, a 22" tall radiator is 3 EDR per section. A 26" tall 3 column radiator is 3.75 EDR per section. How many sections are there to that radiator (from side to side)?
  • BobCBobC Member Posts: 5,174
    That should be 3.2 per section, if it has 8 sections that would be a total EDR of about 25.6. As long as the pipe slope is good it will probably be fine.
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • JUGHNEJUGHNE Member Posts: 7,910
    Should be 1/2" per foot, according to the book. If you can't get this and are over 8' then next size larger.
  • Dave0176Dave0176 Member Posts: 1,172
    The 1" up feed riser will probably support about 24EDR but I'd run the runout a minimum of 1-1/4 at 10'
    DL Mechanical LLC Heating, Cooling and Plumbing 732-266-5386
    NJ Master HVACR Lic# 4630
    Specializing in Steam Heating, Serving the residents of New Jersey

    I cannot force people to spend money, I can only suggest how to spend it wisely.......
  • gerry gillgerry gill Member Posts: 2,996
    The subject of radiator pipe sizing is very subjective. There are many charts from the past that are available and one time just for giggles I took the side profile of a building with its radiators and sized the same radiators using a multitude of various charts and came up with wildly different pipe sizing. My only conclusion, was that any of the charts probably would work, as they were all done by different engineers. But the caveat there, would be that the entire system would need to follow the same chart.

    This does cause us a problem in the present, as we have no idea who's chart was used originally. My best suggestion would be to look around the other pipes and see what sizes were run to the radiators in the rest of the facility. You would want to do this since if you put in a pipe that is larger than the others, I guarantee your radiator will heat, however the next one in line may be starved for steam. If you put in a radiator pipe that is too small (albeit from a chart that an engineer made) the "path of least resistance" will be significantly higher in this pipe, and the radiator may be slow to heat.

    Hope that somewhat helps.

    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • KC_JonesKC_Jones Member Posts: 4,561
    I know it's not proper, but my system (and this is original) has a 40 EDR on the second floor fed by a 1" line. I have a very slow vent on it and I think that's the only way it is working. It only has about 16" of horizontal pipe and then all vertical from there. All my second floor rads are 1" all the first floor are 1 1/4".
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • oopsplumberoopsplumber Member Posts: 14
    The rad in question is at the rear of the house. It is fed by off a 3 inch main and the branch size is one inch and the run is a little over 10 feet. The system produces plenty of steam and my branch is well supplied.

    Some moron contractor installed a baseboard rad and ran 3/4 pipe to it. So instead of running a 2nd line back and tying it into a wet return, (more work) I have a small one pipe steam rad of 25 to 30 EDR which I am going to install and feed with one inch pipe (since that is the size coming off the bullnose of my tee on main) And slope it 1/2 to 1/4 inch per foot. It's going to be straight run (2) 90s and maybe a 45.

    Does anyone see anything wrong with this plan?

    Homeowner does not want to me to cut into main to increase tee size.

    Lastly, should I install a vent which lets the air out quickly or slowly?

    Thanks guys,


  • FredFred Member Posts: 8,503
    Pitch it at least 1/2" if at all possible. It will likely work. I'd start out with a Hoffman #40 (slow vent) or an adjustable vent that you can open faster if needed. The Hoffman 1A has 6 adjustments with #3 being the same venting speed as the #40.
  • JUGHNEJUGHNE Member Posts: 7,910
    Was this a add on room or always there? If there is an original 1" tap there it maybe used to feed some rad for the original room. Maybe plenty of slope and slow vent will make it work. IMO
  • jumperjumper Member Posts: 1,571
    So can get away with small pipe if slope suffices? But safer with even more slope and bigger pipe. How stiff is a 10' 1" pipe?
  • FredFred Member Posts: 8,503
    You don't want to bow the pipe. The right way to do it is to put a couple 45's on the main, at the run-out and configure them to get the pitch you want/need.

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