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Refitting cast iron radiators reducing from 1" to 3/4" at valves

I recently bought a 1900's detached row house which sat vacant for a time. From what I can tell, It had a cast iron hot water steam setup for the upper 2 floors. All of the radiators are missing, but the 1" supply and return piping is intact. It was setup so that the supply and return enter the radiator on the same side. I have already sourced replacement cast iron radiators, but they are drilled for 3/4" fittings.
As far as I can tell, I have two options:
1) Drill out the 3/4" openings in the replacement radiators to 1" NPT and use 1" 90 degree valves/ connectors to most closely follow the original setup. (Yes, I have to drill and tap 1" NPT, there aren't bushings I can remove)

2) Install 90 degree 1" to 3/4" reducers and install straight valves and connectors which require no modification to the radiators.
Is there any major disadvantage to reducing the 1" pipes to the 3/4" radiators with smaller diameter connections?
If done for all of the radiators, and installed with TRVs I can't see a balancing issue.


    JUGHNE Member Posts: 11,021
    "Hot water steam", it is usually one or the other.
  • Jamie Hall
    Jamie Hall Member Posts: 22,952
    Hot water steam? Uh... no. From the description of the radiators having both inlet and outlet on the same side, it's more likely it was steam (although some hot water systems do that too).

    It would be helpful to know which it really was.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • novajke
    novajke Member Posts: 7
    Sorry, steam was a typo. I am rather certain it was a straight hot water system. There doesn't seem to be the complexity of a steam system around the boiler, and the supply and return lines are both the same size. Additionally, there is no trap on the return at each radiator. (Valve on lower port, regular connector on upper.) Either way, even if it was originally a steam system, I will use as a hot water system when I have the boiler replaced.

    The radiators I obtained are most definitely hot water, and they were ran with inlet and outlet on the same side.
  • novajke
    novajke Member Posts: 7
    Also, Thanks for taking the time to reply!
    JUGHNE Member Posts: 11,021
    At the boiler:
    do you have a pump
    an expansion tank
    a sight glass
    temp control
    pressure control
    pop off valve rated at 15 or 30 PSI
  • novajke
    novajke Member Posts: 7
    I wish I could give more detail, but I can't.
    I have nothing near the boiler because it was all stolen/ ripped up. The stripped hulk of a 1950's burnham holiday cast iron boiler remains in the basement. I am having a new hot water boiler plumbed in. This will be a hot water system. I believe that most, if not all of the radiators are plumbed in parallel. Individual pairs of 1" pipes for individual 3rd floor radiators are not teeing off anywhere on the second floor where they come up from the subfloor. I can't really see the plumbing below that due to the drop ceiling on the first floor.
    I know 1" is on the larger side for hot water, but will I cause a massive headache by attempting to reuse existing cast iron lines, assuming they pressure test well? I am mostly trying to get these radiators prepped and ready so that there is enough of a system for my heating guy to actually be willing to revive, rather than tear out and start fresh.

    Thanks for the reply!
    JUGHNE Member Posts: 11,021
    The pressure test is needed. If by chance this was a steam system it may have only been subject to 2-5PSI.
    Your hot water system will see up to 30 PSI.
    It would be logical IMO to test the existing piping at 50PSI.

    IIWM I would go for the reducer method rather than drill/tap CI rads.
  • novajke
    novajke Member Posts: 7
    Great! I was leaning toward this option as well. As far as my research seems to have indicated, old CI may be brittle and prone to cracking when under the stress of being drilled and tapped. (Even for a simple 1/8" vent port) Additionally, the 3/4" fittings will be less expensive than the larger fittings.

    Thanks again for all of the insight!
  • novajke
    novajke Member Posts: 7
    Whenever looking at old posts I always appreciate when there is a follow up further detailing the situation hence I figured I will do the same. It will also be nice to get some experts weigh ins on my current thoughts.

    After taking a good solid look at the heating system of this building, I can say with relative certainty that the original cast iron system was gravity hot water. At some point, the 3 story rowhouse heating was split into 3 separate boilers. The upper 2 floors got new boilers which tied into the black pipe with copper. The behemoth of a gravity boiler (2 inlets, 2 outlets, 5" main loop) still exists in the basement- and apparently was used to to heat the first floor (~1000sq ft) after the conversion- which had cast iron baseboards tied into the black pipe with copper and no circulator. (I can only imagine the heating bills for that system)

    All of the copper was stolen, but I do still have the cast iron baseboards, (which may be salvageable). I hired an old-timer to take a look at the system. Nothing about old gravity boiler jumped out to him as terminal, although he recommended against reusing it for anything. (Apparently, he hasn't seen a gravity boiler in 20 years, which for NY, I think speaks volumes)

    Enough of the gravity system remains that theoretically the system could be restored to its original configuration- however any initial equipment savings will very quickly be lost with 1) an inability to charge for individual apartment heating and 2) the general inefficiency of hot water gravity heating. This would also require tapping out the radiators to 1" and threading a few dozen custom lengths of 1" black pipe to tie between the original fittings.

    Instead, I intend to get 3 replacement CI boilers and run 1/2" oxygen barrier pex to the replacement radiators on the 2nd and third floors. The exposed 1" pipe is individually ran for each radiator, and has virtually no bends (2 x 45's), so I believe that I can snake the pex through without damage. I will use Honeywell Braukmann V110 valves bought surplus since they cost the same as equivalent standard radiator valves. Without the TRV head, they default to open- and if I so choose, I can add the TRV head at a later date to compensate for any room overheating problems.

    Am I completely crazy to want to run the pex through the existing pipe? Anybody want to argue for restoring the gravity hot water? Should I just get slant fins and be done with it?
  • Grallert
    Grallert Member Posts: 638
    I've run pex through black pipe a few times, in fact I'll do just that to preserve the interior look of an old house. Just know, any bend can be a real pia to pull pex. you could use a lube that electricians use to pull sleeved wire through conduit. With a pumped and valved system you'll be fine with 3/4" supply and return fittings on your rads. Sounds like a fun project. Keep use posted.
    Miss Hall's School service mechanic, greenhouse manager,teacher and dog walker