SO I'm curious as to what I'm looking at here (yes its burning coal
).. In this pic (remember, at first glance this apperared to be a cold smoldering fire till I cranked up the camera exposure time) my thinking is that these flames are from carbon combusting into CO2 and CO.
Then in this pic, with the addition of secondary air, the bright blues seem to form up over the little blues in the picture above. These would be CO combusting into CO2?
At this point it's a tough call.
Could the secondary burn yield more output? Or is the extra nitrogen that's added carrying That little bit of extra heat out the chimney. I believe this is where the antiques shine. They possess the extra hardware to extract that heat into the home. Although in my opinion, it may only be a few percent. Where for us with the modern box stoves it's more for viewing pleasure.
Opinions and results may vary, headaches can also occur