I'm the kind of fellow who peruses the internet and books for months doing research, spends alot of time making detailed plans, re-does the plans a couple times, then it never gets done because i can't afford the materials.
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I moved from central Illinois to central Arkansas back around Thanksgiving. Partly because on trips down here to go to a major 4-wheeling event with my friend i fell in love with the fresh air and forested countryside, partly to help my now-disabled friend build a 30x48 shop.
They will be living in the back of it when the bank repos their double-wide trailer house in the next couple of days. We have totally run out of money but have gotten the roof on the new building and the walls halfway up...my friend says he and his brother n sister have lived in worse conditions for months in the past, so they'll survive until we can afford the tin to enclose the building.
When we get it completed we'll open a 4x4 truck shop, do vinyl signs & graphics, aerial photography, and maybe sculpture, so money ought to start trickling in soon.
I built my first 8" rocket mass heater over the last month. The thermal mass is a little short, so the exhaust stack gets hot enough i can only lay my hand on it for a couple seconds. But it stays cool enough for safety.
I remember Mat saying he had to leave the windows and front door open for awhile because his first build was cooking him out of the house. I remember 'Fisherman's Daughter' saying "We have to lay on the floor to breathe". The one-room cabin I built after i moved down here is only 12'x12'. I've found out what y'all experienced firsthand. (Pant...Pant....Gasp)
My friends and friends of theirs who've stopped by to help with the new shop construction are very impressed that 6 hours after i've had a short fire in the RMH, the cabin is 80°.
The feed chamber, burn tunnel, and heat riser are all built from 2"x4"x9" firebrick, cemented together with Rutland refractory cement. The feed is 8"x7" (oops) for a CSA (Cross Sectional Area) of 56 sq in. The burn tunnel ceiling is 8" down from the top lip of the feed chamber. The burn tunnel is 6"x7" for a CSA of 42 sq in, and 10 inches long. I formed a 'Peterburg' tripwire 4" in on the ceiling of the burn tunnel from refractory cement smeared to a sharp ridge. I've yet to build Peter Vandenburg's fresh air injection plate in the front of the feed chamber.
The heat riser measures 7"x7" inside for a CSA of 49 sq in, close to the CSA of an 8" round pipe, 50.24 sq in. From the ceiling of the burn tunnel to the top lip of the heat riser it is 40". This is four times the length of the burn tunnel, and drives the system very well. The top of the heat riser is 2.5" or so from the 'top' of the drum. I don't have a pyrometer yet so i dunno how hot the drum is getting...but it turned a neat shade of blue near the top.
I welded together a three-legged metal stand for the drum to sit on, and built the largest exhaust plenum i could. I'd heard other RMH experimenters warn about choking the system by making the exhaust hole from the drum too small. It is 18" wide, 3.5" high over the burn tunnel to 7" high by the back of the drum (more room). That descends 20" sideways to become 10"x10", then feeds into an 8" tee for the ash cleanout. The pipe inside the thermal mass is 8" and about 18' long before it exits the mass and turns upwards into the exhaust stack.. That's a little short for this unit but i didn't have any more room.
Since this picture was taken, i've filled the thermal mass bench with a mixture of clay-rich dirt, limestone shale, and alot of gravel. I placed broken concrete chunks and melon-sized rocks everywhere they wouldn't impede the flow of fill around the pipes. The tube nearest the room is barely covered and the one by the wall is half covered...that's how i've been running it so far. I'll dump in more mass when i have some spare time, but moving all that weight is exhausting work. I'll probably mix up a soupy batch of red clay and pour it over the last batch of gravel i put in, to fill the small gaps around the gravel chunks and thereby improve thermal conductivity.
The drum ended up being about 5" from the drywall, too close for comfort. So i put sheet metal up on the wall with a 1/2" air gap between it and the drywall. Air can get in the bottom and flow upwards to keep it cooler and help heat the room...like i need another source of heat...lol. I put tinfoil everywhere else i thought it might get hot for added safety.
The T in the exhaust stack is there so i can burn a little paper in the stack to get the air moving in the system, to make it easier to start. I welded metal tabs to some expanded metal mesh, then ran self-tapping screws through the T into the tabs. The mesh sits level with the bottom of the cap...a platform to put crumpled paper on and keep it from falling down the pipe. Then i light the paper, quickly pop the cap in place, and light twisted paper to stick in the feed chamber. The air being pulled into the burn tunnel by the hot updraft in the exhaust stack sucks the flame through the kindling, starting the system with minimal flame in my face.
Today i folded a 30"x10" piece of 'hardware cloth' (metal mesh with 1/2" holes) twice to make a heavy screen to lay over the feed chamber when i need to go up the hill to the construction site and can't stay to mind the fire. That should keep embers from popping out and setting anything ablaze. I try not to leave it while it's running but sometimes ya gotta.
