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Boiler returns “throttled down”?

Hello! I’m new here but been looking on this forum for a few weeks now. A lot of good information! I just purchased my first house and it is equipped with single zone OHW boiler with 36” radiators. I have noticed the previous owners has all of the returns from the radiators “throttled down” with the ball valves. I can’t figure out why they would be like this. Are they trying to keep the heat in the radiators longer? I didn’t notice any increase in the pressure of my boiler it’s in the 12-15 psi when running. Any input would be great! Thanks to all and Happy Holidays!


  • They may have had a thermostat placement problem, and were trying to compensate for some uneven temperatures.
    If you have a modern digital thermostat, is it set up for hot water heating, and is it placed in the ideal location?—NBC
  • hot_rod
    hot_rod Member Posts: 15,427
    I agree that it was probably an attempt to even out the heat output from various rads. Panel rads or cast iron? Really about 3 panel radiators per zone is a good suggestion due to temperature drop.

    Turning down a valve does not equate to more output. Higher flow rates = higher radiator temperature and higher output.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ecobeast88
    Ecobeast88 Member Posts: 3
    The thermostat is set up to run hot water heating. Location is ok. The rads are cast iron. The 2nd floor is always warmer than the lower floor. I’m guessing because hot air rises? Would it result in less heat even if it’s the return being closed? I can see if it was the supply side. Thanks guys!
  • Gordy
    Gordy Member Posts: 9,514
    edited December 2018
    Throttling down would not increase system pressure, but would increase system pump head.

    You say all radiators are throttled down. Are they all throttled the same?

    You say all radiators are 36". That would mean all rooms, or areas heated would have identical heat loads. Not likely.

    My first thought is system balancing. All valves throttled the same would not indicate balancing, or the person tried to balance, and didn't understand balancing.

    So if your observations are correct then the previous owner was throttling the flow rate to decrease output of the radiators in the entire system. if all ball valves are in same position, and the friction losses for piping to each radiator were the same.