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1/2\"PAP for CI radiators?

hot_rod Member Posts: 19,278
in fact you could move 22,000 BTU/ hr at a 20 degree delta T on 1/2".

3/8 pex would actually carry that load.

Run a 40 degree delta t and you might plumb the whole system on 1/2"

hot rod
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream


  • Jeff C
    Jeff C Member Posts: 4

    I'm considering re connecting my cast iron radiators with pex-al pex piping home run style, and would like to use 1/2" if I can get away with it. Ran a heat loss, and the 1st floor comes in at about 20,000 btuh. Looks like the rads design output at 170deg totals about 41,000 btuh. Biggest single rad is 12,750 btuh, with a 50' run round trip to the manifold. Considering the fact that the house is WAY less demanding of btu's than when they were installed 100yrs ago (or whenever), this seems feasable, but I'm not an expert, but a lot of you guys are.
    By the way I piped my bedroom rad (13,600btuh) this way 2yrs ago when I was doing a radiant floor below it, and it seemed to work fine,got hot, but I never cranked it up to see if it would really cook, as I like the bedroom cool.Thanks for your input.
  • Jeff C
    Jeff C Member Posts: 4

    That's what I thought, but expert opinions really count for me. I want to use the 1/2" so I can use copper manifolds with ball valves to be able to balance or even shut down radiators that aren't needed, like upstairs where it's usually too hot. Nice pipe sizing software! Anything like that available as shareware that you know of?
  • Eric L._2
    Eric L._2 Member Posts: 94
    1/2\"PAP for CI radiators?

    I'm going to be doing the same thing.I will be converting my steam system over to water. So you are saying I could move all the BTU's I need to my 680sqft EDR plus oversized CI rads with 1/2" PEX? I plan to use the lowest temps possible with a non condensing boiler.My calculated load is about 86000btu and 1/3 of the rads will have a 50 foot run supply and return (100').Thanks
  • Please

    Don't destroy your steam system by converting it to a hot water system.

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  • Eric L._2
    Eric L._2 Member Posts: 94
    Hey Gordo

    I would love to keep my steam system but unless there is a way to divide it up between two apartments effectively or to realize fuel savings through available technology (ODR,Modulation,Condensing) then I'm going to have to do it. If I can do one or the other of the above then I would keep it in a heartbeat. Thanks

    Eric L.
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