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Gravity system

I have a customer that just purchased a home with an existing hot water gravity heating system. The original boiler has been previously changed out to a gas fired hydotherm ( probably sometime back in the 80's ). The customer is redoing the kitchen and wants to add a small zone of radiant to the system. The room is 11'x 11'. So its only going to be one loop of 1/2" tubing. I am concerned about adding a circulator to the system for the radiant zone. Obviously i don't want to force water through the gravity mains. Will the circulator create unwanted flow through the gravity mains even if it is just for the radiant loop and set up to pull the mixed water through the mixing valve? I don't want to have to convert the gravity part of the system to a pump fed system. Can the house be left one zone and the radiant run via gravity as well? What are my options?


  • kcopp
    kcopp Member Posts: 3,990
    edited September 2016
    Your simplest bet is to have them do electric radiant as floor warming if they are doing tile..... Unless you are up to doing at least partial system re-pipe.
    Especially w/ such a small room.
    The other option is to do a small tank set up, gas or electric. Again it going to add up the cost.
    delta T
  • delta T
    delta T Member Posts: 870
    I agree, either electric mat or tank setup. I don't think its worth it to try and screw with the existing gravity system.

    If you put tubing in the floor and use an electric water heater, keep in mind that if the (now 30 yrs old) hydrotherm fails, you may be able to replace with a modcon and really get some great performance out of the system. Old gravity systems can usually work incredibly well with modcons. If you have tubing in the floor, then you are already set up to hook up to the new system when it happens.