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1910s 2-Pipe Cast Radiators in series loop

Hi all, I'm a new home owner and trying to figure out how to handle my heating system problem. I'm new to all of this as I've always lived in apartments.

I am trying to solve a 'cold room' issue in our 1910 American Four Square colonial home. The house was originally a beach cottage that was retrofitted probably in the 20s or 30s with a 2 pipe steam heating system. This was retrofitted circa 2005 with a forced hotwater system fired by a Weil-McLain Ultra Series boiler. The old cast iron steam radiators were retained and converted for use in this system in most of the rooms of the house with the exception of the bathrooms.

I am not sure who did the work, but the second floor has 4 cast iron two-pipe radiators, and 2 baseboards. The 2 front radiators are on one loop, the 2 rear radiators are on a separate loop, and the 2 baseboards are on their own loop.

I have read online that one should never have cast iron radiators running in a series as the second radiator in the series will not receive adequately heated water.

My issue is with the second radiator in the front loop; it's not getting hot. At first, I believe this is due to the uninsulated copper supply line running up an un-insulated exterior wall to the radiator.

This cold room is a very small room (probably 12 by 7 and will be our soon to arrive baby's nursery.

After realizing the radiator was second in line for the loop, I thought I'd try insulating the PEX supply lines in the loop with the cheap foam pipe insulation throughout the basement where accessible. I have been really surprised by how much this has helped, but on cold days like today (it was 12 degrees when I woke up) it still isn't cutting it.

The other issue is, the room is very small and the only wall that a crib will fit has the radiator on it. So ideally, we'd like to get rid of the radiator and replace it with baseboard.

My idea is that by reversing the flow of the loop and converting the radiator to baseboard... I will be able to send the water through the exterior wall pipe first, through the baseboard, and then to the second cast iron radiator. My logic is that the hot water will pass through less linear feet of supply line before hitting the exterior wall, and in the series, less heat energy will be extracted by the baseboard than a cast iron radiator.

What do you think? Will this work? Or should I have a plumber come in and add a manifold to run these with dedicated supply and return lines for each radiator rather than run them in a loop?

I am not clear why the original installer ran these in a loop to begin with, but I am hoping there was no reason?


  • chasepgt
    chasepgt Member Posts: 6
    a few more details

    My concerns were:

    1. Am I OK to run cast iron and baseboard in the same loop?

    2. Can I just flip the direction of the supply/return by disconnecting and swapping the lines at the manifold?

    3. Do you think that the hotwater reaching the radiator after I change the configuration will be hot enough to adequately heat the room?

    The second loop in our house that has the 2 cast iron radiators running in a loop does adequately heat the second radiator in the loop, but I will say, that the second room in teh loop is significatnly colder than the first room i nteh loop (though not uncomfortable). The supply lines in this series do not use any exterior walls.
  • Ironman
    Ironman Member Posts: 6,868
    edited January 2014
    Series Loop

    No, they should not be piped in series. Also, BB and CI rads don't work well on the same loop as the BBs usually require higher water temps.

    Reversing the flow may help the colder room a bit, but you'll get no more total heat to the two rooms.

    I would not remove the CI rad and replace it with BB: you'll get far less heat output. Have you confirmed that the rads are free of air? Even in series, both rads should heat up.

    All of your questions can only be answered with "it depends" since you've provided no specific info on heat loss, rad sizes, piping, circ's, etc.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • chasepgt
    chasepgt Member Posts: 6
    a bit more info

    Thanks for the feedback.

    Yes, both radiators heat up, it's just that the second one doesn't get hot enough on cold, cold days (I'm assuming due to the fact that the supply line is on an exterior wall with very little blown in cellulose protecting it from the elements. On warmer days (mid-30s to 40s) the second radiator heats the room, but is of course not as hot as the other room.

    I will have to report in later when I get home as to the piping diameter, but I believe the pex supply and return lines are 5/8". This runs to and from the manifold along the basement ceiling to the wall where it attaches to 3/4" OD copper that runs up the walls to the radiators via 2.5" adapters to the old steam pipe.

    I have no heat loss calc and won't bother with one until I finish airsealing and insulating (underway currently).

    I'd estimate that the small room's radiator is 18" x 40" and the other radiator on the loop is 36" x 40".

    Whether there is air in the run, I have no idea what might be symptomatic of this. The radiators are not noisy.

    Each zone has a circulating pump.

    I know I haven't supplied enough info for a strong recommendation... but if you make some assumptions would you do any or all of the following, and in what order (Hoping the issue is resolved by taking the fewest/most cost effective steps)

    A. Re-plumb all radiators in the zone to have dedicated supply and return lines

    B. relocate copper supply and return lines on the exterior wall to an interior location area or conditioned space.

    C. Reverse the flow of the loop

    D. Something else?

    The rest of the house is currently comfortable, it's just this one room that is cold or at least colder so ideally, I don't spend a ton of money redoing the entire system.
  • Ironman
    Ironman Member Posts: 6,868
    EDR Tables

    The attached link will take you to radiation tables from which you can determine the square footage of your radiators. Post that here and we'll have a better idea of the heat needs for those rooms and what should be done.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Steamhead
    Steamhead Member Posts: 15,329
    Another example

    of a botched steam-to-water conversion.

    One of the issues here, besides the different and incompatible types of radiation, is that the original radiators on hot water only put out 2/3 of the heat they did with steam. This is likely marginal at best for the rooms they're in.

    Run a heat-loss calculation of each room and compare it to the available radiation. I bet you find the cause here.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service