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Will switching supply and return on hot water boiler effect heat on radiators?

Dairon421 Member Posts: 80
Hello I recently just recently removed a hot water boiler in basement. I have two supply pipes that are way in the back and two returns in the front. I was wondering since it is Hot water could I just reverse the piping and use the existing supply for the new return and vice versa. My only concern with the is I heard Hot water boilers uses diverter tees and was wondering if switching the pipes will cause any harm to the heat in the radiators. The Supply and Returns are Separate and not in one loop. Its Similar to a Two Pipe Steam main piping set up but its hot water. My second question is do you really need diverter tees?


  • Jamie Hall
    Jamie Hall Member Posts: 23,640
    Diverter Ts are part of "monoflow" hot water heating systems, and they do have to be oriented correctly. However... is your system monoflow? There are several other piping arrangements -- parallel, reverse return, series, hybrids among those... where it doesn't matter as to the piping. Valves, such as checks and zone valves, are direction sensitive, however.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Tim_D
    Tim_D Member Posts: 129
    If the supply and returns are not in a loop it is likely not monoflow. Post some pictures so that we can give you better answers.
  • Gilmorrie
    Gilmorrie Member Posts: 185
    Are you proposing to circulate water "backwards" through the boiler? Check manufacturers' instructions.
  • retiredguy
    retiredguy Member Posts: 930
    I have seen a few commercial jobs where the boiler's supply and return were reversed such as in an H B Smith Model 640/650 or a fire tube steel boiler. The original design engineer insisted that it was done to increase the boiler's efficiency. Did it raise the efficiency, who knows, but it sure made for a good discussion. If you are suggesting that you will reverse the flow in the piping of the heating system, I would not recommend it. Depending upon the type of system you have, it may be possible, but why would you even think of doing it.
  • Gilmorrie
    Gilmorrie Member Posts: 185
    edited April 2023
    Air-removal or air-separation devices may be more effective if on the boiler's supply side - where the water is hotter and air is less soluble. The circulator pump and motor may benefit from being on the return side where the water is cooler. There may be other factors, too, involving the internal design of a hot-water boiler?

    One more issue. Ideally, the expansion tank should be connected to the suction side of the circulator pump. If it is piped correctly to begin with, it will be piped incorrectly if the system supply and return are swapped. Probably, it may still work OK, but....