>The following summary of how steam-heat residential radiators work appeared on
>another list. Is this correct thinking?
>
>1.  The majority of heat tranfer on radiators results from _convection_
>(natural convection), not radiation.  I think it's around 70%-80%
>convection & only 20-30% radiation.  The temperature delta between
>the radiator and the surrounding is not large enough for radiation
>to dominate.  So, they really oughta be called "convectors"!
>BTW - Convection refers to heat txfer from the _flow_ of a fluid
>(air in this case).  By "natural" convection, I mean that there's
>no fan or blower.  Air naturally circulates in the room through
>the radiator.
>
>John Leeke, Preservation Consultant

I'm no scientist, but here's my take on this.  This may be true for _air_,
it probably is, but air is a non-sentient thing, its state can be measured
with but a thermometer.  But in terms of human comfort the radiant effect
on your bare skin from the radiator is significant.

Ever sat in a room in a "modern" rehabbed house where they have installed a
forced air furnace system, but not insulated the walls?  You can have the
thermostat set at 72 degrees, the air is 72, yet if you are in short
sleeves, you feel chilly?  That's because the heat of your skin is
radiating to the cold walls, and you feel chilly.  You go put on a sweater,
you feel better.

That hot 'ol radiator is a mighty fine comfortable thing on a cold day, and
it's not because it has heated the air up to 72 degrees.

____________________________________________
Dan Becker
Executive Director, Raleigh Historic Districts Commission

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