Hot Water Loop off Steam Furnace

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    • #274057
      escartin

      Several years ago we had our steam boiler replaced inand a hot water loop was added to provide heat to our Rec Room through hot water baseboard heat. The boiler is in the basement and the Rec room is on the second floor

      Over the years we placed the pump and check flow valves when they failed. They were changed again last Spring.

      Recently the hot water does not circulate through the entire system. The return pipe is cold, the feed is very hot. When I open the bleed valve on the return pipe
      air escapes and then water flows out of the value. When I close the valve sometimes hot water flows through the return pipe and the system performs like normal for a short time and then fails again.

      I suspect an air leak at one of the solder joints but don’t see any signs of escaping water. Is there a way to determine if the cause of this problem is an air leak and identify the source?

    • #289065
      Harold Kestenholz
      Participant

      A hot water loop off the bottom of the boiler was always meant to serve a baseboard or radiator loop below the water level of the boiler. When there is an attempt to heat water above the boiler water level, there are usually problems of the kind you describe.

      As the water is at or near steam temperature (212F) the pump is subject to water temperatures often beyound its design. Steam pockets develop as the water drops back down from the upper floor, many times creating banging. Any air entrained in the steam settles out at the high point in the loop as the water cools causing pumping rate problems.

      A better solution is to interpose a heat exchanger between the boiler water and the baseboard loop (with a small expansion tank.) There are now relatively inexpensive flat plate exchangers available from boiler manufacturers that can solve most of the problems encountered when using the boiler water above the boiler water level. This makes the baseboard loop a sealed hot water system usable at any height above the boiler with milder baseboard temperatures.

    • #289066
      SylvanLMP
      Participant

      Great Article and Advice Harold BUT you neglected to mention as the steam cools it can and does create a vacuum and thus the air problem with no apparent leaks.

      (packing glands etc)

      Why would anyone try to use a hot water loop from a condensate line for heating ABOVE the boiler is always a mystery.

      Think about if the installer had either put in as you suggest an indirect coil OR A tankless coil like we do for domestic hot water.

      AHHHHH the joys of coming behing the unknowing huh?

    • #289067
      SylvanLMP
      Participant

      Great Article and Advice Harold BUT you neglected to mention as the steam cools it can and does create a vacuum and thus the air problem with no apparent leaks.

      (packing glands etc)

      Why would anyone try to use a hot water loop from a condensate line for heating ABOVE the boiler is always a mystery.

      Think about if the installer had either put in as you suggest an indirect coil OR A tankless coil like we do for domestic hot water.

      AHHHHH the joys of coming behind the unknowing huh?

    • #289068
      Harold Kestenholz
      Participant

      That’s right Sylvan. There are many people who do not know the history of steam heating or what happens to steam temperature water when subjected to pressure changes. The result is an attempt to heat without knowing the consequences. Care needs to be taken when reinventing the wheel. “… where Angels fear to tread.”

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