quantitative radiant heat

Are there quantitative formulations for the amount of radiant heat output based on temperature and surface area? I assume there are, but since I don't know much about radiant heat, I don't know any.

That is, if I have a surface which is 1 square foot and 100 degrees hotter than the ambient temperature, and I ignore convection, what is the radiant heat output from this? I assume the material also matters.

I'm interested in reconciling some of my calculations that, well, I do when I sit around and think too aimlessly. Namely, if we consider a hypothetical "radiator" which is just a sheet of metal(wood, etc), aligned vertically, and I knew the estimated radiant output, I could measure the rate at which the metal loses temperature and determine the effective convective output as well. Then, we could imagine (I do a lot of imagining) experiments where we turned the sheet of metal flat against the ground, or some other orientation, and calculate how the convective output of our "radiator" changes with orientation. We could then determine the hypothetical EDR of silly looking artsy theoretical radiators, like a cube hanging from the ceiling.

-Michael