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Pipe sizing for steam radiators

superdel Member Posts: 2
I have an 1 1/2 inch pipe coming from my basement, through my kitchen (about 8.5 feet). From this point there is about 3 feet of pipe until it connects to the radiator. There is a 1 1/2 inch shutoff valve in this 3 foot section. Right after the valve, it is reduced to 1 inch to connect the radiator. This is a one pipe system. No other radiators are on this 1 1/2 inch line.
My question. What are the ramifications, if any, of replacing that 1 1/2 inch pipe with a 1 inch pipe the whole way? I am doing a remodel and life would be so much easier if that pipe was 1 inch instead of 1 1/2 inch. It runs up through the kitchen and not inside the wall. This is where the Mrs wants a cabinet, and it will be easier to work around the smaller pipe.
The pipe has to reduce to 1 inch to connect to the 1 inch radiator anyway, what is the difference where that occurs?
Thanks in advance for any answers,


  • KC_Jones
    KC_Jones Member Posts: 5,081
    Need to know the EDR of the radiator that is connected to the line to answer that question. If you know the EDR post it, if you don't and can't figure it out post a picture and dimensions and we may be able to figure it out for you. Also some pictures of the piping in question would help. The setup sounds unusual.
    2014 Weil Mclain EG-40
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  • Bio
    Bio Member Posts: 278
    See chart below
  • gerry gill
    gerry gill Member Posts: 3,033
    You will need more than just the EDR of the radiator. Neither you nor we know who's sizing charts were used when the system was designed or what the initial pressure drop considerations were. Where I'm going with this is even if a chart says the 1 inch pipe would work, it may not, if the rest of the system has 1 1/2 inch pipes. It will become a path of least resistance thing for the steam. So go out and look around at the other radiators that are approximately the same size and the same distance from the main and see what size those run outs are. If you drop the size of the runout that you want to drop in size, the best we could say is it MAY work.
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

    Robert O'Connor_12SWEI
  • superdel
    superdel Member Posts: 2
    All of the other radiators in the home are 1 1/2 inch pipes fed directly into the old style standup cast iron radiators. The one in question was changed from a 1 1/2 inch radiator to a baseboard radiator with a 1 inch connection. So the original 1 1/2 inch feed has to be reduced to 1 inch somewhere in order to connect to the baseboard radiator. As of now, it is reduced above the kitchen ceiling from 1 1/2 inch and goes about 3 feet of 1 inch to the baseboard radiator. My question is, can I change the 1 1/2 inch that comes from the basement to above the kitchen ceiling to 1 inch. That is, since I have to reduce the pipe to1 inch somewhere in order to connect to the baseboard radiator, does it matter if it is 3 feet away (as it is now) or 12-15 feet away (if I replace the existing 1 1/2 inch pipe coming out of the basement to the kitchen ceiling)? I hope this clarifies my question. Thanks again for the replies. I really appreciate the time and effort.
  • gerry gill
    gerry gill Member Posts: 3,033
    I'm understanding your question, but your not understanding the answer. In one word-FRICTION. Not being a mathematician, or an engineer, I'm not sure anyone can answer this question with 100% certainty. My only advice is if you are intent on doing this, is to run the pipe in 1 inch, do not conceal it yet, and then test the system out. See if it works. It may work just swell, or it may lag behind.

    Pipe sizing and steam is crazy. I was putting together a class on pipe sizing for the PHCC a year or two ago, and doing my due diligence in the research end of it I uncovered so many different charts written by so many different engineers that made my head spin. I had a sideways view of a building cut in half and I sized the radiators in this building using the different charts, and I came up with wildly different results. Sometimes 2 inch risers, sometimes 1 inch risers, so the only result I ended up taken away from all of this study was I determined that every one of these charts would work if the ENTIRE SYSTEM were sized according to each chart. The key here was not to mix the charts. If one guy's chart said the thing had to be one and a half inch and another guy's chart said 1 1/4 inch the only conclusion I could draw was the engineer who came up with the charts was basing his calculations on a certain friction loss. In either case, when I did eventually do the class I presented these facts to the plumbers and basically told them just because a given chart says they can do something, doesn't mean that they still aren't required to go out and look around the building and get a feel for the pipe sizing with the other radiators, or their new radiator placement may not work, or at least work well.

    I hope that helps. I'm not trying to be a rain cloud here.
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.