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How can I tell if I have a gravity fed system?

wcssuewcssue Posts: 2Member
edited June 11 in THE MAIN WALL
After reading your extensive information on gravity fed systems on this site, I believe that my heating system was at one point gravity fed but I want to confirm that it has been converted. There are two heating zones and there are two circulator pumps at the boiler, one that feeds into the old piping. I also have a pressurized expansion tank for a closed system in the basement . Based on this information can anyone confirm that it is no longer a gravity system?
I plan to install a hydronic towel rack in the upstairs bathroom and I’ve read that they don’t work with gravity fed systems. Any advice?


  • Mike_SheppardMike_Sheppard Posts: 530Member
    Sounds possible. Can you take a picture of the boiler and piping and post it?
    Never stop learning.
  • Danny ScullyDanny Scully Posts: 1,184Member
    If you have multiple Zones and circulators, it’s not a gravity fed system. Gravity systems operate as their name implies, by gravity. Hot water is lighter than cold water so it rises by gravity above it. Also, they typically had an open expansion tank in the attic. From what you’ve described you have a forced hot water system, not gravity.
  • IronmanIronman Posts: 5,091Member
    @Danny Scully,
    Danny, we have on occasion split old 4 pipe gravity boilers into 2 zones when converting them to forced flow. It gives some east/west zoning of the house.

    But I agree about the original setup being only one zone.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • IronmanIronman Posts: 5,091Member
    If you have old black iron pipes that are larger than 2" in diameter, then it's a good possibility that your system was originally gravity flow.
    Pics would really help.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • Danny ScullyDanny Scully Posts: 1,184Member
    edited June 10
    They’re asking if it could still be gravity @Ironman, not if it was.
  • wcssuewcssue Posts: 2Member
    Thanks for your comments. I think you have confirmed that I now have a forced flow system. Any advice on installing a hydronic towel rack/radiator on this system? This is what I’m planning on installing
  • IronmanIronman Posts: 5,091Member
    Water, like most people, takes the path of least resistance. The problem you're gonna have is that the towel warmer will offer more resistance than the old rad's, and thus get less or no flow.

    The only sure way to address this is to run the lines for the warmer back to the boiler and install a dedicated circulator on it. You may get by just adding a circ to the riser going to the warmer, but it's not guaranteed.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
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