1) Does it emit more IR at higher temperatures? In other words, would pumping hot water through/under it produce larger temperature drops?
2) Is it weather proof, or do you still need to find a coating that protects it while not blocking the IR?
It's pretty durable on its own. That being said, as we've moved to the product stage we've packaged it in a way to protect it further.
That said, we are talking about something that has a weird radiance spectrum as a selling point, so, expect some deviation from the standard T^4 curve.