Thank you for the video; most people never get to witness a steam engine in action. I used to drive tractors as a kid, but we moved away from the farm in 1964, and I've never seen any true steam machinery utilized on a farm. Thank you to those who keep it running so that folks like me can view it, even if it's only for fun. No one has ever seen a wood or coal burning boiler run without some type of pollution control, or they would be aware that the smoke from one of these can be fairly black.

The steam coming out was from the safety valves, also known as pop valves. The valves release extra steam when the boiler has a good fire and the engine reaches and exceeds the maximum pressure required to climb this hill. I imagine he came to a halt near the woodpile. This small engine most likely needed to "wood-up."

Of course, pardon me; I wasn't sure how much you knew about the subject. Walls can also be on top...
Apart from the distance from the fire (there should also be a brick arch, or other similar flame deflector separating the tubeplate from the fire proper), I'd be a lot less concerned about tubes, because they tend to be made of steel, whereas fireboxes are rather full of nice stuff like copper. Any excessive incline will have an effect. You might even be able to drown the regulator valve!

Jay is such a kind and sincere person that he is essentially a keeper of transportation history. Who knows how much money he's spent/will pay to keep all those vehicles running! Without him, I wouldn't know as much about transportation history as I do now. Fantastic man, fantastic collection, fantastic videos.

The beautiful thing about Jay is that he can explain his equipment to many different levels of cognition, from the newbie to the ordinary mechanically inclined, to the advanced Mechanic who really doesn't know much about how it all works, and to the general public as equally educational for everyone. He not only covers all of these topics in his narrations, but he's also down to earth in the manner he communicates to people with passion and understanding, making him a fantastic guy all around. Thank you very much, Jay...!!