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radiator paint

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dabrakeman
dabrakeman Member Posts: 552
in Strictly Steam
Not a novel thread but I am starting a new one because most that I have read seem to indicate no issues with Rustoleum Specialty Metallic in a copper metallic color.  It was beautiful when I painted it in June after sandblasting.  Come winter it temporarily gave off odor with the first heating cycles as expected, but, what was not expected was the slow continuous color change with each cycle.  By January of the first winter it had changed from a brilliant copper color to a muddy brown/gold dingy color.  Paint says it is good to 200F.  could it have been because I did not use a primer?



I am now contemplating painting another radiator gold using a VHT engine metallic which I intuitively would have more confidence in from a temperature stability standpoint but the color selection is limited.  The gold is "very gold".  I have plenty of standing radiation for the room to spare so I would prefer to stay with a metallic looking finish.  Also would prefer spray because I believe it goes on much smoother and easier particularly in the interior than brushed on.  Any recommendations out there of a suitable metallic gold paint with more of an antique look than the in your face engine paint gold?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,284
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    The only problem

    with any of the metallics -- copper, gold, silver -- is what is called "emissivity" -- that is, simplistically, amount of heat, in BTU per hour, which a surface at a given temperature will radiate.  We use a nominal figure of 240 BTU/hr at 215 F -- steam temperature -- but that assumes an emissivity around 95%.  Metallic paints will drop that figure to as little as 70% -- even lower, if they are clean and in good condition.  This effectively derates your radiation to that figure -- say 150 BTU/hr or so.



    You can see this effect for yourself if you have an IR thermometer -- aim it at a regular painted surface and then at a metallic painted one which you know are at the same temperature; the metallic one will show a lower temperature, since an IR thermometer doesn't actually measure temperature, but rather energy radiation rate.



    Now then, there are two problems evident with metallic paint.  First, your radiation may wind up undersized for your space.  Second, your boiler may now wind up quite significantly oversized for your radiation.



    Or you may have both problems at once...



    There have been a lot of threads on painting radiators; look around.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Paul48
    Paul48 Member Posts: 4,469
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    Ding-Ding!

    Jamie gets the prize! You've selected the one type of paint they say not to use on radiators.
  • dabrakeman
    dabrakeman Member Posts: 552
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    emissivity

    As I pointed out in the initial post the radiator I was able to find for this room is slightly oversized as it is.  Some drop in emissivity is tolerable.  I don't think I am the only one of this mind since many of the room radiations were initially setup assuming you have windows cracked to let fresh air in.



    The purpose of this thread was more to assess how color fast various paint types are.  I would not like to see other people experience the negative results that I did.



    By the way, the metallic painted radiator in the upstairs room that discolored still can overheat the room.

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