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Gravity Boiler System


  • Jason_13
    Jason_13 Member Posts: 299
    Will not heat on gravity, must use a circulator.
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,449
    Hot water will not fall to the radiator. The piping you show is called a heat trap. Only forced circulation will make hot water move downward to emitters.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    JUGHNE Member Posts: 9,751
    If the return to the boiler from those rads went under the floor then there might be some gravity flow. I have seen this in an old house but they wanted the basement rads removed as there was enough heat from the boiler in the basement.
  • jumper
    jumper Member Posts: 1,831
    Buy a light weight panel and mount it high. Who wants stinking circ pumps?
  • Your replies are appreciated! From what I knew / understood, I was not comprehending how such an installation would work by gravity for the basement? You confirmed my suspicion/s! Now my question is:

    1. With six cast iron free standing radiators in the basement.
    2. With three cast iron free standing radiators and five baseboard radiators (4', 10', 10', 2' & 2') on the main floor
    3. With four cast iron free standing radiators on the top (third floor)

    What size pump (how many gpm?) would likely be the most appropriate?
  • Brewbeer
    Brewbeer Member Posts: 616
    Pump sizing depends heavily on the diameter of the pipes conveying water in the system, and the total "round trip" length of those pipes.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
    JUGHNE Member Posts: 9,751
    Were the basement rads original to the old house?
  • JUGHNE, to the best of my knowledge, all of the free standing radiators and baseboard heaters are all original. The diameter of the largest pipes and obviously reducing down while extending away from the boiler, and subsequently 'enlarging' while returning back to the boiler is 1-1/4" Sch. 40 Steel Pipe. The longest run (through the piping path, is roughly fifty feet of 'supply' piping, with the expected fifty feet of 'return' piping. All of the free standing radiators have half inch Sch. 40 steel pipe connecting to them. Any helpful information that can be provided regarding properly sizing a circulation pump for this installation would be appreciated.
  • Steamhead
    Steamhead Member Posts: 15,329
    Not a gravity system with all 1/2" radiator runouts. This would have had a circulator from the get-go. I doubt even the "accelerated gravity" systems (think Honeywell heat Generator) used pipes that small.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,449
    With the piping layout you posted a diagram of, and what @Steamhead said, it sounds like you have a typical circulated hot water system.

    Some pictures of the actual boiler, it's piping, and some of the T's that go to the radiators, as well as the radiators themselves would be helpful. Just to be sure you don't have a monoflow which would be typical for an older water system. You may have a simple direct return, or a reverse return. How you describe the pipe diameters getting subsequently smaller sounds like a direct return.

    Can you diagram the system piping?
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Solid_Fuel_Man, I am well acquainted with Monoflow tees & such systems. Also, the boiler has been removed and disposed of (neither by me). The customer has not chose a replacement boiler. However, regardless of the boiler chosen, I presume an appropriately sized circulation pump will be necessary. And I would like to be ahead of the game. I could provide a "system piping" diagram. However the above diagram is an accurate representation (of less detail of course). If a "system piping" diagram is truly necessary, I could provide one. If such is the case, how detailed would you like? Pipe Diameters, Pipe Lengths, Fitting Type/s / Sizes, etc... please confirm?
  • Gordy
    Gordy Member Posts: 9,514
    edited January 2017
    In order to size a circ "poperly" you need to calculate the head loss of the piping, and fittings to the farthest convector, and back from the circulator. This involves pipe diameters, lengths, and developed length of all fittings in that circuit.

    If the circulator is sized to the highest head loss circuit (usually the farthest one) the other circuits will be fine.