On Aug 10, 8:13 pm, Wayne Whitney wrote:
On 2007-08-11, wrote:

The radiant barrier is essentially a layer of aluminum foil on one
side of the plywood. The aluminum foil reflects heat. In the
attic, the barrier is on the bottom side of the plywood, so would
reflect heat back into the attic, which is generally where I am
trying to get the heat away from. Isn't this counterproductive????

The key idea is that if an object is in equilibrium with its
surroundings, then the emissivity e = 1 - reflectivity r. So a highly
reflective surface has low emissivity. This allows the radiant
barrier plywood roof deck to heat up from the sun without radiating as
much heat into the attic as normal plywood. A side effect of this is
that the radiant barrier plywood will be hotter than normal plywood
would be under the same conditions.

Cheers, Wayne

If I understand you, a shiny hot surface will be a poor emitter of
heat, even if it is much hotter than its surrounding air? And a flat
black pipe will be a much better heater/emitter than will a shiny
pipe?
I've got a lot of general background stuff, but I never picked up on
that one. It's intuitively obvious that a flat black surface would
absorb heat, but no so obvious that it would also be a better
emitter. I got some readin' to do...