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25,000 EDR WITH 5/8” PAP?

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OhioRuss
OhioRuss Member Posts: 29
will I be happy running 2 cast iron radiators, each with own TRV, off one 5/8 feed and return? I would prefer each having its own 1/2”, but space in the floor cavity is tight and they are in the same corner of the house, only different floors. This is a new install in a 150 year old solid brick house. I'm looking at Lochinar or TT boiler, Alpha pump and manifold. Thx

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  • Jamie Hall
    Jamie Hall Member Posts: 23,458
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    Can't be 25,000 EDR. Unless those are mighty big radiators... what is the real number, preferably (since this seems to be hot water) in BTUh that you want to put through there?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • OhioRuss
    OhioRuss Member Posts: 29
    edited February 2019
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    They are the 3 column Rococo rads, 38” tall. If I’m reading the charts correctly, that is 5 EDR per section. The largest is a 14 section rad, with a 12 section on the floor above. The heat loss of the lower room is 13,000btu, the one above it is 11,000btu. The house is a 150 year old four-square and all brick, including the interior walls. I will have to run pipes in the living area of the downstairs to get to the upstairs rads. If I can run one line to each corner of the house and run the 2 rads with TRV off each respective line, I will save a huge amount of labor.
  • Jamie Hall
    Jamie Hall Member Posts: 23,458
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    OK. I get an EDR for the big one of 70, and the other of 60. That gives me roughly 17,000 BTUh for the big one and 14,400 BTUh for the little one -- on steam. On hot water that will be less -- perhaps 2/3, or about 12K for the big one and 10K for the little one. Which is just barely enough for your heat loss. It's also 31K total -- which may be too much, at the required temperature, for a 5/8 inch PEX line. Someone else can figure that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • OhioRuss
    OhioRuss Member Posts: 29
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    I did my calculations for hot water at 170 and came up with similiar numbers. If that is too great a load for 5/8, am I better off feeding 2 rads with one 3/4” or should I go back to original 1/2” to each. It’s not easy drilling through the 24” walls and 4” floor joist.
  • Jamie Hall
    Jamie Hall Member Posts: 23,458
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    You should be OK with the 3/4 inch.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gordy
    Gordy Member Posts: 9,546
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    At a 20 degree delta 5/8” pex will move about 32,000 btus at 3.3 gpm. About 11 feet of head per 100’. 3.9 FPS.
  • Gordy
    Gordy Member Posts: 9,546
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    PAP also has a 200* temp max.
  • OhioRuss
    OhioRuss Member Posts: 29
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    Thanks, everyone.
  • Ironman
    Ironman Member Posts: 7,379
    edited February 2019
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    Caution:
    Whatever size pipes you run to the new rad's, they must be PROPORTIONATE in size to the rest of the system.

    Water takes the path of least resistance. If there's old large gravity sized piping going to the rest of the system and you size the new piping based on modern hydronic design, you're gonna get little or no flow in the new lines.

    If you're stuck in that scenario, the new lines would need to be on their own circulator.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    GordySuperTech
  • Gordy
    Gordy Member Posts: 9,546
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    ^good point!