I am the wife trying to ask a question for my husband so there could be some giggles before I am finished.
Lumpy wants to build a firebox to heat iron using coal, bricks and who knows what else. He had to draw me a picture to just ask his question. He has a pipe coming up through the middle into which he will blow air.
His question is: would it be more effective to harness the hot air coming from the fire and return it to the pipe or use cold air through the pipe.
When I asked why he thought one might be better than the other, his reply was that there might be less oxygen in the hot air after being burned. This might make cold air more efficient. Please comment!
