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Tapping a radiator

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pnm2
pnm2 Member Posts: 56
The bottom half of this radiator never gots hot.



Since the air vent is located too low (from my understanding), I thought I'd try tapping a hole maybe two thirds of the way up to see if that will make a difference.

Firstly, is this the product I need in order to do that:
https://homedepot.com/p/Drill-America-1-8-in-Carbon-Steel-NPT-Pipe-Tap-and-R-High-Speed-Steel-Drill-Bit-Set-2-Piece-POU1-8NPTW-DRILL/304750418

Secondly, how should I plug the original hole? Will I want these two items, or is there a better way:
https://homedepot.com/p/The-Plumber-s-Choice-1-8-in-Closed-Galvanized-Steel-Pipe-Nipple-10-Pack-1800NPGL-10/309100845
https://homedepot.com/p/The-Plumber-s-Choice-Malleable-Iron-Pipe-Cap-Threaded-Fitting-150-lbs-Application-Black-Pipe-Cap-1-8-in-Pack-of-10-0018BMCP-10/308315754

Thanks!

Comments

  • neilc
    neilc Member Posts: 2,703
    edited January 2021
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    NOPE,
    that vent is exactly where it wants to be,
    that bottom 1/4 of rad will have cooler condensate, and cooler air there,
    does the rad heat evenly across all the top and upper third?
    Are you cold / uncomfortable in the room it serves ?
    known to beat dead horses
    EdTheHeaterManethicalpaulLS123
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,840
    edited January 2021
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    If there is air in the radiator it won’t be hot. If there is steam in the radiator it will be hot. Steam and air don’t mix. (think of it like oil and water) Steam is lighter than air so it will float on top of the air. Placing the air vent higher in the radiator will vent less air because the steam (that is on top of the air) will close the vent before all the air gets out.

    That is why air vents are located in the bottom 1/3 of radiators. Another reason why steam only radiators work better than radiators that work for both steam and water. The steam goes to the top of the first section and spills up forcing air out the bottom before it spills up in the next section. Picture filling an ice cube tray by only putting water in the first compartment and letting the water spill over to the next compartment, forcing the air out of that compartment, then on to the next compartment and so on... just picture it upside down where steam is forcing the heavier air down out from the compartment.

    When there is a top connection as there is on a water compatible radiator, The steam can travel to the next radiator section without forcing all the air out. So the top of the radiator gets hot first all the way across. Only after a lot of time passes will The condensing water migrate down the lower walls of the radiator and heat the entire radiator. In milder weather the thermostat may be satisfied before the entire radiator is hot

    It is part of the design and it works

    This falls under the jurisdiction of department of “if it ain’t broke, don’t fix it”

    Respectfully submitted,
    Mr.Ed
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    ethicalpaulLS123
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,840
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    In answer to your questions

    If you were going to move the vent anyway, the drill and tap combinations you posted would be the proper size.

    And no I would just use a plug in lieu of a cap and pipe nipple.

    But you don’t need to worry about it because you won’t get any benefit from your efforts

    Yours truly,
    Mr.Ed
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    ethicalpaulLS123
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,529
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    @pnm2
    Go ahead and add a second vent if you want. I am assuming the radiator is slow to heat. Adding a second vent should cause no issues and no harm in trying. You can always plug it if you don't need two vents
  • pnm2
    pnm2 Member Posts: 56
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    Thank you, everyone, for the responses. I'm pretty sure Dan Holohan wrote in "We Got Steam Heat!: A Homeowner's Guide to Peaceful Coexistence" that the air vent should be located at the upper half of a radiator, no?

    @EdTheHeaterMan Only the top half of the radiator gets warm, and only the area closest to the valve gets what I would call "hot", and the room definitely is not warm enough.
  • Jamie Hall
    Jamie Hall Member Posts: 23,310
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    The location of an air vent on a one pipe steam radiator is significant, no question. Perhaps the best way to describe where it should be is somewhere in the middle third of the height. It also is important to consider whether the radiator is connected across the top or not. If it is, you want the vent lower, as otherwise steam will race across the top and shut the vent before the lower part of the radiator sees any steam at all.

    There is also a complex interaction between the speed of the vent and the boiler cycle length. A slow vent, for instance, with a shorter boiler cycle, may see the radiator heating very poorly.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pnm2
    pnm2 Member Posts: 56
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    @Jamie Hall The radiator appears to be connected at both the top and bottom. It sounds like you're saying that, indeed, the air vent should usually by located somewhere at the upper half of the radiator, as opposed to the lower half.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,840
    edited January 2021
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    pnm2 said:

    Thank you, everyone, for the responses. I'm pretty sure Dan Holohan wrote in "We Got Steam Heat!: A Homeowner's Guide to Peaceful Coexistence" that the air vent should be located at the upper half of a radiator, no?

    Top of radiator for water heat to get the air out because water is heavier than air
    Bottom 1/3 of radiator for steam because steam is lighter than air
    Both mediums to not mix with air for the most part.


    @EdTheHeaterMan Only the top half of the radiator gets warm, and only the area closest to the valve gets what I would call "hot", and the room definitely is not warm enough.

    Now that is a problem that needs attention. Perhaps the vent is not allowing enough air out of the radiator fast enough. this would be remedied by a vent with a larger orifice. Perhaps the burner is cycling off by the thermostat before that radiator is finished venting. Perhaps the main vent(s) if any are not venting the air from the main making the problem radiator do all the air venting for the main and the branch to the radiator.

    1. Where is the radiator located in reference to the radiators that are operating properly? for example: last on connected to the main, or middle of other radiator branches, or second-floor, or third floor
    2. How long does the burner operate during a cycle? For example: 4 minutes on 4 minutes off, or burner stays on for 15 minutes, then off for 10 minutes, or the call for heat is only 23 minutes and the burner stays on the whole time.
    3. At what pressure is the boiler operating?
    4. How many other radiators are on this system?
    5. Pictures of the near boiler piping from several angles from ceiling to floor.

    This info will help in solving the problem.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    mattmia2
  • pnm2
    pnm2 Member Posts: 56
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    @EdTheHeaterMan

    1. The radiator is on the third floor of a 3-story house, so definitely somewhere close to the end of the branch, if not the end itself.
    2. I don't know how long the burner generally operates, but I've "stress-tested" the system but pumping up the thermometer and letting things run for a long time, and even then the bottom of the radiator doesn't hear, though the top will definitely get its hottest.
    3. The boiler is 0.5-1.5 PSI.
    4. It seems as though there are two branches coming out of the boiler. The amount of radiators they serve altogether is somewhere in the neighborhood of 15-20.
    5. I believe there's a chance this may be related to a "carryover" problem I discovered at one of my main vents (discussed and pictured here https://forum.heatinghelp.com/discussion/181967/main-vent-questions#latest and here https://forum.heatinghelp.com/discussion/182083/water-spurting-out-of-a-main-vent-opening#latest), but because bringing in a new installer to redo the job will be costly I thought the relocation of the air vent might be cheap and easy enough to try first to see if it'll make a difference. Furthermore, if it is caused by the carryover, it surprises me that more radiators aren't affected.
  • jhrost
    jhrost Member Posts: 57
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    Most of the pros here recommend the middle, and on page 107 of Lost Art Dan Holohan implies the middle. I was able to pick up an old copy of Winter Air Conditioning at a book sale. A lot of the info here is based on experiments with Research residences where heating experiments were conducted by the engineering Dept of the University of Illinois . They seem to agree with Jamie Hall that it should be in the lower third of the radiator. Just to summarize them a bit , if the vent is at the top - a large air pocket will exist opposite to the entrance of the steam - this portion of the radiator will be ineffective - the proper location is the lowest possible point on the radiator at which steam will exist - but not so low that condensate will clog the inlet to the vent valve.

    With wet steam being a common problem maybe that is why the middle location is a good compromise, Don't forget though that referencing the advice of the old timers Dan Holohan also states that putting in a second vent can help an oversized radiator or any radiator that is difficult too heat. I've tried this myself with some good results - if you've got vents around and the right size drill bit it doesn't cost you anything to try. Of course you don't want to turn your radiators into Swiss cheese either - make sure you drill level so any water in your vent can drain back to the radiator.
  • Jamie Hall
    Jamie Hall Member Posts: 23,310
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    Another approach to a radiator which is slow and at the far end of a long riser or runout is to put a good fast vent on the riser just before the radiator. That way the radiator vent doesn't have to do the heavy lifting to get the air out of the riser and runout, and can be left to control the radiator.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,840
    edited January 2021
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    So it appears that a second vent may help. You would want to locate the second vent at about the same location regarding the night from the floor but perhaps in a different column. The same thing may be accomplished with a single vent with a larger orifice. I’m not familiar with the orifice sizes (or venting capacity) of the different radiator vents available. Perhaps one of the other steam experts have more experience in this area. @EBEBRATT-Ed or @Jamie Hall deal with steam more than I ever did.

    Edit: Looks like Jamie already answered this while I was typing this comment based on the time stamp.

    Respectfully Submitted,
    Mr.Ed

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Grallert
    Grallert Member Posts: 644
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    I think you simply need more venting. That 1/8 hole will vent that radiator. You could as an experiment install a valve at that vent location start the boiler and open the valve. I bet it heats all the way, if that's what you want. That will prove I think your slow venting. The engineers and designers located that vent tapping for a reason.
    Miss Hall's School service mechanic, greenhouse manager,teacher and dog walker
  • MilanD
    MilanD Member Posts: 1,160
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    This setup was done to get the balancing done on a loooooong run out to a big radiator that heated poorly. There were other issues with undersized mains, risers, and so on, but this helped a lot. 

    What you can try is just taking off the vent altogether and checking if the radiator heats up fine. If that's the case, you just need more venting to it/on it, whether a faster vent or a two slower ones, or one before it on the rad riser. Try simplest solutuons first.

    Just keep in mind that whenever you change venting in one place it will have an effect on the entire system, all else being equal. You may also help the balancing by slowing down venting on other rads while speeding it up here.

    Good luck! 
  • mattmia2
    mattmia2 Member Posts: 9,655
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    I don't think any larger or move of the vent will make more of the radiator heat, but a faster vent will likely make it heat earlier in the cycle so it will release more heat per cycle. If it is on the 3rd floor there is likely a lot of pipe in the riser that can only vent through that radiator (or perhaps a radiator below it also heats slowly and needs more venting but has other nearby radiators that heat faster and make it less noticeable)