I was reading in the rocket mass heater book about the trip wire and P channel. My question is how hot should the barrel get on top. I have an adjustable barrel height and found 2 inches from the riser to produce the most heat. I also made a welded removable angle iron inlet with an adjustable plate for air restriction at the front of the burn tunnel. When I fill the fire box with pallet slats and choke down the front of the inlet I can make the barrel soar over a thousand degrees quickly? Does this mean its burning better? What heat is usually at the barrel top? I have an 8 inch square heat riser and the inlet is a hair smaller with the angle inlet frame, about 7 x 7-1/2 inches. I have temp gauges all over and it gets to 400 at the bottom of the barrel and 200 along the horizontal exhaust when the top is 1000? If I run the barrel top at 500 the exhaust is about 160.