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RobG Member Posts: 1,850
How do traditional radiators predominantly operate, radiation or convection? I would like to hear peoples opinions as It came up in another thread.


  • Jamie Hall
    Jamie Hall Member Posts: 15,411
    How about...

    "both"!  For a useless answer.  Or... "it depends".  Not surprisingly, there is a fair amount of radiation -- you can feel it if you stand near a warm radiator.  However, I believe that the major part of the heat transfer is by convection -- although I'll be the first to admit that I've not seen a really scientific study on that.  Rather, my opinion -- for that is all it is -- iss based on two things.  First is the plain geometry question: radiation operates only by line of sight to a cooler object.  Second is the observation that we rate radiation -- quite successfully -- based on the total surface area of the radiator, not on the flat plate area (which would apply to radiation).  For instance, a 10 section, 5 tube radiator of more or less typical geometry has a flat plate area of about 6 square feet -- but an EDR ("equivalent direct radiation") of 50.  Third is that it is quite possible to put a radiator in an enclosure and, provided the enclosure permits circulation, get almost as much heat out of it as if it were in the centre of the room.  Fourth is that you can put a radiator behind a couch (not touching!) and the room still is warmed -- but not that much the couch.

    Now hopefully someone will come up with a genuine lab. study!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • RobG
    RobG Member Posts: 1,850

    Does anyone else care to chime in? I don't necessarily disagree with Jaimie as his physics skills are quite beyond mine. However I don't quite agree either based on my practical experience

  • SWEI
    SWEI Member Posts: 7,356

    and you can prove it with an IR gun.
  • RobG
    RobG Member Posts: 1,850

    The question is which they do predominately. I have a hard time believing that they are 50/50.
  • ChrisJ
    ChrisJ Member Posts: 11,492

    If I had to guess, I'd say convection more, maybe 60/40?

    Curious why you're asking?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • RobG
    RobG Member Posts: 1,850
    Just wondering

    Just wondering. Since they are called radiators, I would assume that they operate predominately on radiation. After all, convectors convect. I assume it's not a stupid question as nobody seems to know an answer definitively
  • ChrisJ
    ChrisJ Member Posts: 11,492
    edited June 2014

    No, not a stupid question.

    I assume radiators got their name just because no one really knew at the time.

    Convectors 100% work on convection, as does baseboard heat but baseboard has a different name.

    From what I've seen personally in my home I'd say radiators work on convection more than radiation but I still think 60\40 or 70\30. When you get one of my radiators full of steam the amount if air movement is insane.

    This is a picture of curtains ballooned up from heat flowing up and out of the radiator. Our new curtains I think have the bottoms sewn together to stop this.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • RobG
    RobG Member Posts: 1,850
    edited June 2014
    Outdoor air reset

    This is what got me thinking, on OAR depending on the size, we can run rads at very low temps (granted they are over-sized for the space). Baseboard will not convect at temps nearly as low even if they are over-sized. Maybe it all comes down to temp versus /and surface area?

    I probably should have posted this in the main wall. Sorry
  • Mark N
    Mark N Member Posts: 1,090
    The answer is in Dan's Books

    Page 113 of We Got Steam Heat. A freestanding cast iron radiator gives up about 60% of its heat by convection and the remainder by radiation.
  • RobG
    RobG Member Posts: 1,850

    My question was more oriented towards hot water heat.That's why I should have posted on the main wall.

  • I believe it changes

    AT low temps, the output is more radiant since the convective air currents are weak,  As the water temps rise, the convective currents increase, increasing the convective output.  I believe the convective output forms and more u-shaped curve when plotted against water temp because of the increased air speed through the radiator, where the radiant output is essentially linear.  This would parallel the heat loss characteristics of a home.  The heat loss through building materials is essentially linear, but the air leakage rate accelerates more as the outdoor temp drops.
    The Steam Whisperer (Formerly Boilerpro)

    Chicago's Steam Heating Expert

    Noisy Radiators are a Cry for Help
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