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In the process of converting two pipe steam system for old church to hot water. The old radiators are the column type but have top and bottom push nipples. The old steam supply is connected to bottom and the old condensate return is connected also to the bottom opposite side. We plan on drilling and tapping the top of the radiator to vent the air out. The question is with the flow through the bottom push nipples all the distribution through the radiator will be dependent on natural convection (hot water rising and cold water falling) in each section. Will this provide adequate heat or should we re-pipe each radiator (which would be difficult) with return on top?



  • nicholas bonham-carter
    steam to hot water conversion

    you may well have enough leaks from the old system, so that the problem will not be heat, but keeping people dry. just pressurize the system with 30 psi soapy water, and you will see what could be in your future. i would plan on new piping, and rads and you should be O.K.--nbc
  • Steamhead
    Steamhead Member Posts: 16,904
    Hope the lawyers don't get you

    there are too many things that can go wrong with these conversions. That's why my company does not do them. 
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 23,453
    Why, oh why

    are you doing this?  I sincerely hope that there is a very very good reason indeed, for you are in for a myriad of problems, of which how the hot water flows through the radiators will be by far the least of your worries.

    This is not to say that conversion of steam to hot water can't be done; it can, and sometimes it even works pretty well.  What it is to say is that it is very rarely a good idea, at least in my humble opinion.

    Ideally you would get the steam system working properly; it isn't that hard to do, and there is a lot of help available right here on the Wall, and sometimes there is a good steam pro. right in your area.  It would surprise me greatly if getting the steam system to work right wouldn't be a great deal cheaper than changing over.

    However.  If your heart is set on hot water, item 1 is going to be to check all the piping and radiators for leaks, even pinholes.  NBC's approach is as good as any, but I would add a bit to it.  Pressurize the entire system to 30 psi with water (I wouldn't use soap, as it is hard to remove completely) and close it up with a pressure gauge on it.  If the pressure gauge drops, you've got leaks, even if you haven't got gushers.  All -- and I do mean all -- the leaks will have to be fixed before you do anything else.  I would plan on replacing most of the piping and, probably, a good half of the radiators at this point.  This is probably just as well, as it is quite likely that the piping arrangement which works so well for steam will work for water; leaks or no, significant repiping will be in order to control where the hot water goes and which radiators get it.

    Having done that, you also need to check to see that you will have enough radiation.  Keep in mind that a radiator fed by steam is at about 210 Fahrenheit.  A radiator fed by hot water is at, at the most, 180 and more likely 160.  That difference may not seem like that much, but it is -- your radiators will put out only about two thirds as much heat as they did on steam.  Will that be enough?  If not, what do you plan to add?

    But as I said above, why, oh why, are you planning to do this?  I am not against a good hot water heating system, planned as such -- they're great.  But if you already have a steam system, fix it up!  Don't change it!  We'll help you fix it!

    Just Don't Do It! 
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Yes, Why?

    I wondered this myself. 2 Pipe steam is a great system. If it's not working properly it would be probably be a lot more economical to fix it than go to hotwater. In a situation like an old church or a hall where there is little insulation and the heat is turned off a lot of the time, steam also has the advantage in that the pipes don't freeze.
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