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.

Radiators piped in series.........

Solid_Fuel_Man Member Posts: 2,646
I was at a customer's house yesterday who had an EFM stoker/oil boiler and the whole house had CI rads.  He said this system was put in in the late 90s.  The boiler he bought used, the radiators were salvaged from several old buildings.  This system was piped in copper, and all the radiators were connected in series.  My guess is that they were originally two-pipe steam as all of them used a lower tapping, and the upper tapping on the opposite side.  With the supply being the lower one and the return being the upper one.  Isn't this totally wrong?  He said the house has heated well in the last decade, but wow I was under the impression that it was a no-no to pipe CI in simple 3/4" series and shouldn't the supply be the top tapping to force the cooler water out and not just diagonal flow up and out?  I just wanted some incite, as I've never seen anyone do this before.

Thanks to the much respected wally wet-heads

Serving Northern Maine HVAC & Controls. I burn wood, it smells good!


  • kcopp
    kcopp Member Posts: 4,390

    correct. Either a monoflow, reverse and return or a manifold set is best. It will be uneven heat. Some people are in to that.....
  • icesailor
    icesailor Member Posts: 7,265
    Just because:

    Just because someone piped it like that doesn't mean that it is right or they knew what they were doing.

    Hydronic hot water heating is extremely forgiving.

    But like that little boy in the poem, "When he was good, he was very, very good. But when he was bad, he was AWFUL".
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Seems like

    it is two for two.  Series, and the return at the top.  I was just surprised it heated.  There were two loops serving a 2,000 square foot first floor, so maybe there is some forgiveness in the relatively short loops with smaller EDR on each loop.

    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • hot_rod
    hot_rod Member Posts: 21,841
    flow direction

    I don't think is all that important, as long as the iron is "touched" by the fluid it will warm. Initial air removal may be easier with supply in the bottom. Here is a pic Siggy took of a panel rad heating up. Notice how the temperature moves across the entire radiator.

    I'm going to infrared some cast rads with feed and return on the bottom connection to see if it warms evenly after a period of time. My hand feels it is fairly consistent after an hour or so.

    As far as series piping, you just need to account for the temperature drop across each rad, just as you do with fin tube baseboard.

    With a home run, manifold piping you can balance each rad, the TRV takes over the temperature regulation.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • knotgrumpy
    knotgrumpy Member Posts: 211
    Great images!

    If the water goes in one hole it would seem it's gotta go out the other eventually.
  • bob_46
    bob_46 Member Posts: 813
    Reinvent wheel

    Exhaustive study of radiator piping , heat output and temperature distribution were done

    at the University of Illinois in the first half of the last century .
  • icesailor
    icesailor Member Posts: 7,265
    Series Piped Radiators:

    Geez, it's hard enough to keep the temperature "close" between the first baseboard and the last one on a copper fin tube. Then, you want to try it with radiators?

    Just don't ever put the thermostat in the room with the last radiator. The first room will need the windows open.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646

    As always the knowledge on this site is extraordinary!  The dead men at Illinois University, did a great job and was a great read for an early Sunday morning before getting ready for church.  The link is much appreciated and enjoyable.

    Thank You All.  
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • icesailor
    icesailor Member Posts: 7,265
    Supply or return on the top:

    Sometimes, supply or return on the top isn't a problem. It can get to be a problem if they are on the same side. The water can go straight up on side and not heat the radiator. If they are diagonal, it might work diagonally. I've put a pipe in the bottom or the top to get the water to flow to the other side of the radiator. Its a matter of figuring it out, and trial and error.

    Cast Iron radiators shouldn't be series looped. The first radiator is red hot while the last one is just getting warm.
This discussion has been closed.