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New baseboard not getting hot

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dan526
dan526 Member Posts: 6

Hello,

New to the forum and just tackled my first plumbing project at home. I removed two old baseboard radiators and replaced them with high output baseboards upstairs in my house without any leaks or disasters.

First room I replaced (farthest from boiler) works fine and puts out plenty of heat, the other room where I replaced the heater (closest to boiler) is cold.  I installed both with a bleeder valve on the return side and water comes out of the cold heater. After a lot of bleeding it will warm up but then go cold again.  One thing I noticed after I finished the installs is that the old radiators had what looks like a check valve on the supply side.  I didn’t install any check valves in the BB’s - could that be part of the problem?

So far I’ve tried bleeding at the baseboard, purging air from the drain valve on that zone of the boiler, and increasing the pressure to around 25-28psi and bleeding.  Water just doesn’t seem to want to find its way through that one line closest to the boiler

This is for hot water heat with an oil burner in the basement.  I have two zones, ground floor and upstairs. All is good on the ground floor and 2 out of 3 heaters upstairs. 

Including a drawing of the layout.  Can anyone help me figure out why that one room is cold?

Thanks in advance,

Dan

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,094
    edited March 2021
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    You need to think like the water. If I was hot water, where would I go? (that is from a seminar by Dan Holohan I attended over 30 years ago.

    Now some pictures of the near boiler piping from far enough back to see from floor to ceiling. From different angles too. That will help with the process. Since you have 2 zones, I assume there are 2 thermostats. The section that does not get any heat, is it on a thermostat that is getting heat elsewhere?

    There are two possible reasons for no heat. Air in the loop or the new section has way more resistance to flow than the section that is getting heat. Another issue may be the pipe size. 3/4" pipe can only allow 40,000 BTU of heat to leave the boiler. High output baseboard being fed by only 1/2" pipe does not seem like a good fit. 1/2" pipe can only handle 15,000 BTU of heat. @ 700 BTU per foot (I'm guessing 700 for high output) you cant expect to use more than 20 feet of baseboard.

    Here is a good resource for you to study. This is my GoTo text when I was teaching this subject. http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf It may help you with this project.

    Respectfully submitted,
    Mr.Ed

    P.S. I added some relevant info to your drawing.

    First. Where is your circulator pump? Red or Green or somewhere else?
    Second. The 1/2" pipe handles about 1.5 gallons Per Minute (GPM) so the 2 hot zones are moving a total of about 3 GPM. 3/4" pipe can move about 4 GPM, so that leaves only 1 GPM left for the zone that is not heating.


    pictures will help.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • SuperTech
    SuperTech Member Posts: 2,186
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    Did you replace any tees? Your drawing looks like a diverter tee reverse return setup. Flow through the tees depends on a pressure drop. Alterations can change the balance of the system. Were the baseboards that you removed cast iron? 
  • dan526
    dan526 Member Posts: 6
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    First, thank you both for the fast replies!

    Ed - I was thinking like water and thinking that once it left the boiler it would be more likely to head toward the 3/4 rather than the 1/2 at that first tee.  Also, my cold baseboard has a copper 90 in the wall, a 90° pex elbow right before the baseboard inlet and a copper 3/4 90° going into it. All the same on the exit side. 

    On the other side of the house where I also replaced a heater I had more access and was able to install without any elbows except the copper 3/4 90° going into and exiting the heater.  

    I replaced the further baseboard first and had the system up and running and was having the same issue where the closer room was still cold even with the older radiator so I thought it might ne something other than just the resistance from 1/2 piping and elbows. Maybe because I removed that diverter/check valve without replacing?

    Circulator pump is at red in your drawing. Also, I only drew out my upstairs zone only.   All three of those rads in drawing are on same zone and same thermostat.  Including two pics of boiler. Circ pump closer to me is for upstairs and return line further is also for upstairs.  

    SuperTech - old baseboards were not cast iron. I’ve included a pic of the old tee that was removed at the supply side of the old radiators. Also in the background is what the old radiators were.  I had one of those in each room. It’s a finned element in a big metal box. 

    Thanks again for your help!
    Dan
  • Jamie Hall
    Jamie Hall Member Posts: 23,441
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    This may be a simple flow balance problem. Are there any valves on the system which control flow to the individual radiators or zones? If so, try closing the valve which is letting water through to the radiators that get nice and warm, and make sure any valves to the cold radiator are open. If that helps, try opening the valves you closed until you get more even heat.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • dan526
    dan526 Member Posts: 6
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    Jamie - I was thinking it would be nice to be able to shut a valve that goes to the hot baseboards to help the flow to the cold one but I don’t have any such valve in the loop. Considered plumbing one in actually. 
  • BDR529
    BDR529 Member Posts: 290
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    You answered your own question. Furtherst works.. Look at how it feeds and returns.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,094
    edited March 2021
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    I can see you have a purge valve setup. and it appears that you are using it to remove air. Is there a way to make the cold loop the least resistant to water flow? You would need full port ball valves on each of the three 1/2" takeoffs or branches. I believe you still have air in the cold loop.

    The weight of the cooler water going down will assist in the pump pushing the heated water up. That pump is not very powerful. Otherwise, you would hear a lot of velocity noise every time the thermostat called for heat. See this illustration


    By placing a full port ball valve on each 1/2" supply or return pipe, you could change the path of least resistance and move that air out of the problem loop.

    This is the "Think like water" I was talking about.

    Respectfully submitted
    Mr.Ed

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    dan526SuperTech
  • dan526
    dan526 Member Posts: 6
    edited March 2021
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    Ed - that’s exactly what I was thinking of doing with adding valves to direct water to the cold pipe only.  And yes, I was purging air there at the boiler. 

    I can install shutoff valves in the basement before it makes its way upstairs, right?  I’ll try that this week.  

    It may be a few days but I’ll be sure to follow up with results. 

    Thanks again and thanks for taking the time to make those illustrations.
    Dan
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,623
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    @dan526

    Water will take the path of least resistance always......when the radiators re not air bound.

    If you bleed it and get no air just water than you have a flow issue....not an air issue.

    I would put valves on the hot radiators to increase the resistance there. I wouldn't add resistance to the cold circuit.
  • hot_rod
    hot_rod Member Posts: 22,258
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    If you do add valves consider actual balance valves so you can see the flow or get a more accurate adjustment. They are not a lot more money compared to ball valves. If you go with a plain valve, look for a globe style valve.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • dan526
    dan526 Member Posts: 6
    edited April 2021
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    Hot rod - so do you think there is a chance I will need to keep the other line partially closed even after I am able to purge air from the cold line? Is that why you recommend the globe valve over a ball valve?
    Thanks,
    Dan
  • dan526
    dan526 Member Posts: 6
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    @EdTheHeaterMan and everyone else.  Thank you for your help!  I ended up installing a full port ball valve near the boiler before the supply makes it’s way to my two hot baseboards.  Closing this valve while refilling the system allowed water to flush through that cold baseboard. I then opened up that valve and didn’t have much trouble purging air at the other spots.  

    I’m happy to say that I’m getting perfectly balanced heat at all three spots now according to the IR therometer. 

    I did also purchase some 3/4 copper elbows to replace 1/2” pex 90°s I used on that cold baseboard but I didn’t have time this weekend to get those in.  That will help the flow and eliminate a bottleneck. 
    Going to take out that short vertical pex line and elbow and replace it with a 3/4 copper elbow.

    Thanks again!
    Dan