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.
If you get significantly high and lasting temperatures when you restrict airflow to the feed tube, that would indicate that you are approaching the exact air/fuel ratio for efficient combustion. Letting more air through means that the system is diluted and maximum temperatures are lower, possibly giving a less efficient burn (and certainly sending more room air out the chimney).
My feeling would be that it is better to run it hot like that and pump lots of heat into the mass, then shut it down and seal it up (after the fire is completely out) to keep room air in, versus running it slow for twice as long.
Thanks, I'm still debating the mass material. I was looking at a volumetric thermal mass table and rammed earth has a higher value than adobe. Its just damp clay soil tamped in layers. This I can purchase from the local sand and gravel yard.
i am thinking about repurposing an existing chimney that was used for a LP burning boiler exhaust. A chimney sweep told me a conventional wood stove would burn way too hot for the material the chimney is made out of. what kind of exhaust temps does one typically see? thanks!
A properly built RMH will have vertical stack temperatures of 140F- 250F
I have seen my J tube hit 350F a few times, after 12-14 hrs of non-stop burning... when it was -10F outside.
I regularly use HVAC pipe in my RMH builds, in the mass and going up to the roof. I only use black stove pipe where it exits the mass or is a high traffic area.
Your chimney sweep is correct, any conventional wood stove would melt the HVAC pipe quickly.