Post by blackearthbert on Feb 11, 2010 13:16:07 GMT -8
I have been on some "off Grid" type sites lately discussing Rocket Stoves for Thermal Mass heating. Been able to help some and have also learned a lot.
I make All Steel Core Rocket Stoves with Hot Gas Discharge Boxes. Please see my Blog @
blackearthrocketstoves.blogspot.com/
One thing I see in many you-tube, and other picts about Rockets and their construction that makes me wonder, is the lack of insulation to break the thermal bridge or connection with the Earth or an external wall. I use 2" of closed cell insulation (blue or Pink depending on load) and have also been using Thermax (no more though). I put down plastic then 2" foam then cement backer board to spread out the load. Very little heat transfers to the earth or through an exterior wall.
When I do an install for a client I insist on the foam and a 4" duct for Outside Air (OA). Also a way to seal off the Burn tube top and the OA duct once the user is done burning. I usually bring in the OA duct near the top of the burn tube opening. To seal the Burn tube opening I try to find an old round charcoal grill top and use a refractory plug for the OA duct opening.
Doing the math for cubic feet of OA sucked into a dwelling with no OA duct is surprising to say the least. It's one of the most efficient ways to throw away the hard earned heat you just tried to fill the dwelling with. A large living room can have its total air volume changed in less than an hour. And that sucks if it's 10 degrees outside and that's the air you exchange it with. Also the Rocket continues to draw and now goes into cooling mode. Now you are losing hours and hours of radiant heat from your thermal mass. So sealing off the burn tube and the OA duct are really an integral part of the claimed efficiency of the properly functioning Rocket.
My stoves install reasonably easily. You can surround them with anything non-combustible like COB or Urbanite, or local sand mixed with concrete. The only requirement is to have one layer of fire brick around the fire box and horizontal burn tube. You can do the bricks or leave a 3 to 4" space and pack it with refractory cement if that's easier for you. You can do the Hot Gas riser in bricks, but refractory cement mixed with vermiculite and contained with a sheet metal tube works better as it doesn't take so long to heat up.
I have figured an easy to make this sheet metal tube if there is nothing "found" that will do. The tube should be around 19" in diameter or 59.6" in circumference. Five 12" stove pipes clipped together instead of just to themselves will give you the tube you need. If you think it's too tight just cut off one seam and sheet metal screw it together for a slightly smaller diameter. You will need another short section to get the height you need. Spend a little time un-bending the pipe sections to get a nice even round shape.
Another "trade secret" is a way to get tubes for your thermal mass. Many silos on farms are not being used any more with the advent of Plastic Tube Silos. I have been harvesting 8" to 9" silo filling pipes. These are the steel pipes that go up the outside of the silo for blowing silage in. You can get them way cheaper than heavy stove pipe and they are thick enough to gas or wire feed weld to make 90's or Tees.
Another thing I devised is to abandon thermal benches or platforms. Why make a bench or bed that's too hot to sit or sleep on? I'm installing interior walls (floor to ceiling) or hip walls (3' to 5' high). The wall configuration provides at least twice the radiant area, configures the heat transfer pipes in a more vertical placement for better draft and makes a nice shelf for raising bread dough or drying clothes. I will do an install in a greenhouse/dwelling this spring and hope to heat the Rocket thermal mass wall with the sun during the day and significantly cut down on wood use.
My steel cores have air tight clean outs, are internally smooth for great draw, and you don't have to have masonry skills to install one. Also my hot gas discharge box is a real improvement and helps overall Rocket performance So, Rocket On......................
Regards
Bert
I make All Steel Core Rocket Stoves with Hot Gas Discharge Boxes. Please see my Blog @
blackearthrocketstoves.blogspot.com/
One thing I see in many you-tube, and other picts about Rockets and their construction that makes me wonder, is the lack of insulation to break the thermal bridge or connection with the Earth or an external wall. I use 2" of closed cell insulation (blue or Pink depending on load) and have also been using Thermax (no more though). I put down plastic then 2" foam then cement backer board to spread out the load. Very little heat transfers to the earth or through an exterior wall.
When I do an install for a client I insist on the foam and a 4" duct for Outside Air (OA). Also a way to seal off the Burn tube top and the OA duct once the user is done burning. I usually bring in the OA duct near the top of the burn tube opening. To seal the Burn tube opening I try to find an old round charcoal grill top and use a refractory plug for the OA duct opening.
Doing the math for cubic feet of OA sucked into a dwelling with no OA duct is surprising to say the least. It's one of the most efficient ways to throw away the hard earned heat you just tried to fill the dwelling with. A large living room can have its total air volume changed in less than an hour. And that sucks if it's 10 degrees outside and that's the air you exchange it with. Also the Rocket continues to draw and now goes into cooling mode. Now you are losing hours and hours of radiant heat from your thermal mass. So sealing off the burn tube and the OA duct are really an integral part of the claimed efficiency of the properly functioning Rocket.
My stoves install reasonably easily. You can surround them with anything non-combustible like COB or Urbanite, or local sand mixed with concrete. The only requirement is to have one layer of fire brick around the fire box and horizontal burn tube. You can do the bricks or leave a 3 to 4" space and pack it with refractory cement if that's easier for you. You can do the Hot Gas riser in bricks, but refractory cement mixed with vermiculite and contained with a sheet metal tube works better as it doesn't take so long to heat up.
I have figured an easy to make this sheet metal tube if there is nothing "found" that will do. The tube should be around 19" in diameter or 59.6" in circumference. Five 12" stove pipes clipped together instead of just to themselves will give you the tube you need. If you think it's too tight just cut off one seam and sheet metal screw it together for a slightly smaller diameter. You will need another short section to get the height you need. Spend a little time un-bending the pipe sections to get a nice even round shape.
Another "trade secret" is a way to get tubes for your thermal mass. Many silos on farms are not being used any more with the advent of Plastic Tube Silos. I have been harvesting 8" to 9" silo filling pipes. These are the steel pipes that go up the outside of the silo for blowing silage in. You can get them way cheaper than heavy stove pipe and they are thick enough to gas or wire feed weld to make 90's or Tees.
Another thing I devised is to abandon thermal benches or platforms. Why make a bench or bed that's too hot to sit or sleep on? I'm installing interior walls (floor to ceiling) or hip walls (3' to 5' high). The wall configuration provides at least twice the radiant area, configures the heat transfer pipes in a more vertical placement for better draft and makes a nice shelf for raising bread dough or drying clothes. I will do an install in a greenhouse/dwelling this spring and hope to heat the Rocket thermal mass wall with the sun during the day and significantly cut down on wood use.
My steel cores have air tight clean outs, are internally smooth for great draw, and you don't have to have masonry skills to install one. Also my hot gas discharge box is a real improvement and helps overall Rocket performance So, Rocket On......................
Regards
Bert
