Alan Murray

Nice, I like.

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 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.

One more question. I was just reading the Rocket mass heater book, and it say's you can use un screened clay soil for the bench with less sand. Am I correct in assuming the sand is strictly for preventing cracking? If so how would dry clay soil packed in a box around the exhaust work? Doesn't the water in the clay just make it pack harder or does it cause a catalytic reaction like in cement?

I think I will make a couple boxes out of plywood and fill one with packed stone dust and one with stone dust and rocks then keep checking them with a I.R. thermometer. Thanks for the reply's

Thanks Glen. I don't want a cob fill as I may have to modify this set up and there is 3 feet of snow and the frost level where I live is about 4 feet deep. So, I would have to buy the clay to make the cob and I would have to fill buckets of water in the house and truck them down to my shop. If I can find a dry fill that can prove this set up will perform to my needs I can refill it with cob in the summer. My thinking is that if stone is the best material then stone dust that packs hard would have little air so it should work almost as good?

So with stone dust being easy to pack would that be better than sand?

I just built a rocket mass heater in my shop. Im trying to get ideas for a dry fill for the mass. Does anyone know if crushed stone will be good, it packs very well. They use it for driveways up here? I want to build a box out of cement board around the exhaust and fill it?