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Radiant was tied into baseboards and have low heat issues

I recently purchased a house that had some work done and I found some issues and trying to correct them without ripping everything out. The 2nd floor bathroom has radiant heat in the flooring, which then feeds the baseboards to the rest of the floor. By the time the water gets into the kids room, its pretty cold and the baseboards have almost no heat output.

The main zone feeds 2 floors lower and upper, the lower level is teed off and works well. After the tee the water enters a mixing valve to step down the water and then into the radiant floor. I also see that the pex is smaller diameter than the baseboard so I think there may also be a pressure loss going on.

My only bright idea is to reverse the flow so that I can use hotter water into the baseboards first and then by the time it makes its way to the radiant its cool enough.

Any thoughts?


  • Jamie Hall
    Jamie Hall Member Posts: 22,897
    Without significant repiping, the idea of reversing the flow sequence in that upstairs arrangement is certainly worth a try (who ever thought that would work as is? Oh well...). That way by the time the water gets to the radiant floor it might even be a reasonable temperature for the floor...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 9,409
    The baseboard needs different temp than the radiant, you cant feed them from the same supply unless you feed high temp water to the baseboards and mix it down at the connection to the radiant.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,525
    edited November 2022
    The mixing valve will need to be removed from the current location. Putting the water thru a mixing valve backwards will not work.

    I don't believe that you will get the flow rate needed for the radiators to go thru the radiant tubing. I think the best plan is to pick a location between the radiant tubing zone and the radiator zone (they should be 2 separate zones) and run a 3/4" PEX pipe back to the boiler room to make a common return pipe.

    Here is an idea that will allow you to leave the mixing valve in the existing location.

    If this is a close approximation of your current piping design:
    Then this is an easy fix. Find a location upstairs between the bathroom and the high temperature radiators and place a Tee fitting (as indicated in the green circle). Run a 3/4" PEX pipe from that tee fitting to the boiler room. That is now a common return for the Radiant and the Hi Temp.
    Reverse the Hi temp radiator return line in the basement and make that the supply line for the Hi Temp zone.

    Add a small pump for the Radiant loop after the mixing valve Mix port to circulate water thru the low temperature loop.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Niceshoes6
    Niceshoes6 Member Posts: 3
    The mixing valve will need to be removed from the current location. Putting the water thru a mixing valve backwards will not work.
    I was planning to have the pipes re-routed before the mixing valve and just raising the temp on it.
  • Ironman
    Ironman Member Posts: 7,342
    IDK how that zone is getting any at all, but your pics are not inclusive enough to see the entire piping.

    A mixing valve MUST have a circulator down stream of the “MIX” port, pulling out of it as Ed has stated. You can’t simply reverse the flow.

    You could re-pipe it with the radiant taken of from the baseboards return as he stated. The only problem there may be with that is the radiant would still be controlled by the thermostat for the baseboards and may not remain on long enough to sufficiently heat the bathroom. Radiant floors are very slow responding heat and should be on their own zone and thermostat.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Niceshoes6
    Niceshoes6 Member Posts: 3
    Thanks for the drawing Ed. Thats pretty much exactly how it is. The difficult part will be the re-route since the radiant goes in / out on either side of the bathroom. Id probably have to rip it all out.

    I know I cant reverse the flow through mixing valve, but since its located in the basement, I was thinking of taking the output of the mixing valve and sending that into the 2nd floor return and then feeding the current input feed into the return. I think the mixing valve may not even be working right in its current location but if it is, then I could send higher temp water into the bedrooms first and then by the time it hits the radiant its lower. Currently I get floor temps of 98F on the rad floor.

    Id rather sacrifice the bathroom heat for the bedrooms. The last bedroom is 64f today, the bathroom is 74f, with therm to 69, clearly out of balance. Thermostat is in hallway, which gets heat from lower level.

    What affect will this have on my flow since it would stay in the larger baseboard tube longer, then into the smaller one? The baseboards are getting choked I think now as well.