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What is the correct/original pipe size for my radiator?

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When I moved in the radiator valves were either stuck open or closed so I replaced them.
The living room radiator had a 3/4 valve so I replaced that.
Now I see that the original iron pipes had been replaced with 3/4 copper.
As best I recall, the tee off the main is 1inch or maybe 1 1/4 inch.
The LR radiator is 3 column type, 9 inch wide, 37-38 inch high, 15 sections.
So I figure
5 sq ft per section . If 170 deg F 150 BTU per section if 160 deg F then 130 deg F per section. So 10K BTU for the radiator?
What was the likely original pipe size?
Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.

Comments

  • Steamhead
    Steamhead Member Posts: 16,832
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    Are there bushings in the radiator to reduce the size of the connection for the 3/4" copper?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    eclecticmnMad Dog_2
  • bburd
    bburd Member Posts: 912
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    If this is an old hot water system, the original piping was probably sized for gravity flow. With forced circulation the pipes can be much smaller.

    Bburd
    eclecticmnMad Dog_2
  • eclecticmn
    eclecticmn Member Posts: 121
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    Thanks. Yes to the bushing. I just measured the threads going into the radiator valve and OD is 1.65 inch so 1 1/4 pipe which the bushing takes down to 3/4 near the floor. If memory serves, the tee off the main for that is 1 1/4 later reduced down to 3/4. I should have just measured the radiator valve to start with.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • Steamhead
    Steamhead Member Posts: 16,832
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    bburd said:

    If this is an old hot water system, the original piping was probably sized for gravity flow. With forced circulation the pipes can be much smaller.

    Correct if ALL the radiator pipes on the system were downsized that way. If only one is, it won't get as much flow or heat.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    bburdMad Dog_2
  • pecmsg
    pecmsg Member Posts: 4,845
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    My system was originally gravity. All risers were 3/4” black iron. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,519
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    If it is pumped water and the rad is good for 10,000btu 1/2" would be large enough. But as @Steamhead pointed out if all the other rads have larger pipe and this one is the only one with smaller pipe you may not get enough flow.

    See if you have any similar sized rads and what are they piped with?
    Mad Dog_2
  • JimP
    JimP Member Posts: 87
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    How’s it working now? If you replaced all the valves you should be able to close the valves and limit the flow to radiators that you feel are too hot.
    Mad Dog_2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,922
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    What brand of valve are you using?  Mad 🐕 Dog
    eclecticmn
  • eclecticmn
    eclecticmn Member Posts: 121
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    After I moved in over 10 years ago I went to the local good, old supply house, Gopher Plumbing. I bought what they gave me which was AY McDonald. I looked closely at this radiator and have another corrosion problem and another post.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
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    You don't have a gravity system . Force flow a 3/8" riser would work . The distribution system would be needed to give you better input . But first question what problem are you trying to solve ?
    I have enough experience to know , that I dont know it all
  • eclecticmn
    eclecticmn Member Posts: 121
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    At first I did not have a problem to solve, I was just curious and trying to map out the system for some summer work. I might valve off some more radiators so I do not panic in winter as I do know. While working the basement den trying to move pex pipes for newer kitchen cast iron radiators to replace the wood stove. I noticed two copper pipes jammed into a tight space next to a beam then noticed it was 3/4 copper reduced down from the 1 1/4 tee. Some had speculated that my 3/4 slant fins never worked because they were 3/4 reduced down from 1 inch tee and a circulator pump might have helped so I just wondered why the LR radiator seemed to work fine. Then I saw the corrosion.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
    edited February 2023
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    How old is the house ? Is it a one pipe supply ? One pipe running around the house with tees and risers running up to radiation ?.... Before you change anything understand the system first .
    I have enough experience to know , that I dont know it all
    reggidennis53
  • eclecticmn
    eclecticmn Member Posts: 121
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    I am told it is a 2 pipe direct return system, based on my drawings. The house was built in 1915 but was added on to also long ago. I could not find any old photos or drawings.
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
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    It could be a gravity system , a sign would be the extensive use of 45's and different pipe sizes .Upper floor risers where piped smaller to add resistance of the gravity flow . Adding a circulator would change the original design . A low head circulator would be the best choice . Any add on could be an issue and best to be on a different zone .
    I have enough experience to know , that I dont know it all
    eclecticmn
  • eclecticmn
    eclecticmn Member Posts: 121
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    For future reference, what is an example of a low head circulator?
    Home owner near Minneapolis with cast iron radiators, one non working slant fin now ripped out, and hot water heat.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
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    Three speed circulator set on low speed . Just enough to lift the flow check .....
    I have enough experience to know , that I dont know it all