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change old gravity system

ddenny Member Posts: 75
I'd like to change a 100 year old gravity system to a conventional hot water system with a new boiler and circulators. can I use the old radiators rather than installing new baseboard? I want to cut out the old piping where it connects to the radiators then connect the radiators in series with pex tubing.


  • Rich_49
    Rich_49 Member Posts: 2,766
    edited August 2013

    piping arrangement are they connected in now ?   Think series is a bad idea with rads . I would lean toward 2 pipe reverse return or parallel manifold .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    edited August 2013
    Repiping old radiators

    Series piping would not be a good solution. Search for " parallel reverse return" here. Are there balancing valves on the radiators now? If not there may be some restrictors in some radiator inlets to prevent some rads from getting all the hot water.

    Your old radiators would be an ideal match for a modulating- condensing boiler, with outdoor reset.

    Remember to do a heat loss on the house first to determine what size boiler you need. SlantFin have an excellent heat loss program which works on tablets, and smart phones, and excellent boilers as well.

    You could use some thermostatic radiator valves, to give you some measure of zone control.

    Don't get suckered into using an instant hot-heater as a boiler or it may burn more fuel than you are now.if your budget is tight, look into the Lochinvar "solution", which although not a condensing boiler, does offer outdoor reset.--NBC
  • Jamie Hall
    Jamie Hall Member Posts: 23,449
    And could I add...

    Why are you set on cutting out the old pipe?  If it isn't leaking, it shouldn't be that hard to convert it to either the parallel setup or reverse return -- either of which would work.  A little more work and you can zone it.

    The only reason I'd mess with the old piping is if it were seriously in the way of some remodeling.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JStar
    JStar Member Posts: 2,752

    Keeping the old piping will maintain the massive amounts of thermal mass in your system. This will allow you to greatly control your comfort levels, and boost system efficiency.

    And, do not pipe the radiators in series. Leave the radiators and piping as is, unless they are leaking. Even then, I would replace with similar piping.
  • ddenny
    ddenny Member Posts: 75
    parallel reverse return piping


          what is parallel reverse return piping? I typed it in the search engine and it referred me to the table of contents of a 700 + page book.

           will this kind of piping work on a gravity system. I guess I only have to change the piping around the boiler correct?

           the boiler is very large and it's oil fired. It's a small old house but uses a lot of fuel. I think she wants to stay with oil.                                   

                                                                                    thank you      

  • SWEI
    SWEI Member Posts: 7,356
    Parallel Reverse Return

    Parallel just means the radiators are all supplied from the same source (and not piped in series with one another.)

    Reverse return helps make the system easier to balance.  Seep p.12 of http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_8_us.pdf 
  • Paul Pollets
    Paul Pollets Member Posts: 3,656

    I'd keep the old piping and install TRV's on each radiator. Make sure the new system is "pumping away" from the new expansion tank. Remove the attic expansion tank, which is most likely steel, and not "pre-charged" with a diaphragm.

    Radiators in series is not a good idea.
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