Rocket mass heater build (time for a rocket stove subform?)

Hi folks,
As some of you know, I've been researching rocket mass heaters for quite a while and have planned to build one for several years. Now that I have "down time" during my recovery from some serious health issues, I took the time to build this rocket mass heater this fall as part of my rehab process, for mind and body.

I found a cheap used barrel stove on Craigslist, cut it in half with an angle grinder and used the side with the door as a frame to build the rocket stove. The other half is being used as a "manifold" for the masonry bench/bell next to the stove. More on bell theory and a great resource on rocket mass heaters here: Batchrocket.eu - Building

I mixed cement and poured in it the barrel stove half with the door, as a foundation for the big 18"x9"x4.5" firebricks that form the outside structure of this stove as well as the walls of the heat storage bench.

I used vacuum formed ceramic fiber risers for the round vertical chamber that the firebox exits into, I lined the firebox itself with 1" ceramic fiber board for insulation, than laid firebrick according to the size and shape of the firebox as recommended by the European researchers that published the website at the link above.

 

In a rocket stove, secondary air has to be introduced immediately in front of the riser. Other builders and researchers have used various steel channels, pipes or tubes to introduce secondary air (see Batchrocket.eu - Applications) but they burn out due to the intense heat in the riser, 2000-2400 degrees F.

I decided to use the ceramic fiber board and the firebricks to create a simpler secondary air introduction method that wouldn't be subject to deterioration like the metal tubes/pipes. Air enters under the lower left and right hand corners under the firebrick liners, travels behind the vertical firebrick next to the riser and through the channels in the vertical ceramic fiber board beside the slot in the riser.

 

Looking good Brian!

Gary

 

The combination of a quick intense fire, lots of secondary air, high temp effective insulation and the turbulence and increased "speed" of the fire and smoke passing through the narrow vertical slit in the ceramic riser tube lets the rocket heater achieve close to full/entire combustion within the riser tube.

At the 2200-2400 * F temps achieved in the vertical ceramic riser, all the combustibles and particulates in the smoke are entirely burned without the need of a catalytic combustor, making for incredible efficiencies and very little if any combustibles or pollutants going up the chimney.

The riser exhausts within a 55 gallon drum, which rapidly cools the smoke, quickly discharging the heat to the outside air through the relatively thin metal of the barrel. Because the outside air cools the metal of the barrel so rapidly, it never gets hotter than 650-800* F on the top of the barrel, and the metal of the barrel does not degrade.

 

The smoke cools as it falls down the inside of the barrel, exiting into stove pipe at the bottom, and entering a masonry bench/bell. The hot smoke expands in the large space inside the bench, and gravity forces the gases to stratify, with hot gases rising and cooler gases sinking as it gives up its heat to the large mass of the masonry bench (mine will be close to 3000lbs). Exhaust gases then go up the chimney from the bottom of the bench near the floor at 180-220* F, having given up more of its BTUs inside the house than a typical wood stove, whose smoke is much hotter exiting the chimney. This is a "blind ended" bench with some coming into the bench then exiting on top of each other. Stratification by physical properties of expanding hot gases ensures the heat rises throughout the length of the bench.

Because of the complete combustion of volatiles/particulates within the riser, there is nothing in the exhaust to precipitate as creosote, and it can be exhausted at a much lower temperature.

 

I'm building my bench/bell out of the same large firebricks, at 55lbs a piece, and using a double layer of 2'x2'x2" thick pavers as a lid. I'm using ceramic blanket insulation between the layers instead of mortar. The bench will be 8'x2.5' high x2' deep.

In rocket mass heaters, fire only burns in the "batch box" firebox for 1 to 1 1/2 hours before it goes out. The mass of the masonry bench absorbs the heat of the initial fire then, similar to a Russian masonry stove, gently radiates heat into the house for many hours after the fire goes out.

Because the masonry bench (bell in Russian terminology) absorbs the heat then releases it long term, and there is such a high efficiency of fire in the highly insulated ceramic riser, and the exhaust is so much cooler than a wood stove, utilizing a much higher level of available BTUs, rocket mass heaters supposedly use half or less the amount of firewood as regular wood stoves to provide a similar amount of heat.

We'll see ;-)

 

I'm using two 6" stove pipes between the barrel and bench because this is a common bottleneck in this type of stove, and two pipes will make it breathe easier. Also I included a bypass T with a damper for cold startups, to prevent smoke back with a cold bench. I also included a clean out T with a removable cap if a small fire starter needs to be placed in the flue on cold start up to develop draft.

 

I think a rocket stove subforum would be awesome.

 

Grizzly Adam ??

 

That was discussed once and it was determined that the Pre-EPA Woodstoves and Fireplaces forum is the place for the rocket stove threads. Maybe it should be relabled non-epa instead of pre-epa.

 

Do you want to move this thread then Grizzly Adam ? (Although I think this technology deserves its own subforum, like "Masonry and rocket stoves and rocket mass heaters" as it's a completely different concept than pre, post and non EPA stoves.)

 

I can pop it over there.

We stuck a pin in the subforum idea until the amount of rocket stove discussions deemed a need for the subforum.

 

Great, thanks.

 

I'll bet Eric VW has some videos and pics that would fit in here also

 

Got to love a build like this!

Help me out, where is the outside exhaust?

 

In post #9, both pics, bottom pipe going to the left.