Rocket mass heater in a barn

Hi permies. I'm planning to build a 6 inch rocket mass heater inside of a barn here in the sierra foothills. I'd like to run my ideas across all of you here on the forum, and then I'll likely document the build here as well. I've built one other 8 inch system, pretty much just following the layouts and directions in the rocket mass heaters builders guide, which I'm using to help with this one as well.

Some pertinent information:
We are at about 2700 feet with a mild climate, average winter low around 32f, sometimes down into the 20s.

The building is an uninsulated barn, with old board and batten siding with holes everywhere, definitely not air tight. It's about 2100 square feet, including the stalls on the perimeter, but we would really only be aiming to heat the large center room which is about 600 square feet.

We are turning this center room into a shared community space, and we would like to have a warm place to spend time together. I'm thinking to go with the heat the people not the air strategy since the building isn't insulated, thus the RMH.

I'm planning to go with a 6 inch system, primarily because we already have most of the triple wall insulated stove pipe for the exterior chimney, and that stuff is quite expensive.  I'm also considering using a bell stratification chamber in the mass bench, made out of 55 gallon barrels cut in half lengthwise, since even single wall stove pipe is expensive and I already got some barrels for free.

The placement of the heater core is pretty much limited by the doors to the outer stalls and the easiest place to get a chimney outside.  There is small gable end wall between a higher and lower section of the roof, about 3 feet tall. I'm thinking I can run the chimney pipe either horizontally or diagonally through this end wall, high up near the peak of the roof, and then 3 feet above the ridge.  I know that's not the ideal chimney, but I would rather do this than punch a hole through the nice metal roof I just installed.  Given that the building is so full of holes, I'm not too concerned with a competing chimney effect, and I'm bringing the exit flue up right next to the barrel to help pull the gashes up and out.

Even though the room is quite large, about 20x30, because of the doorways there is only a 7' x 10' corner in which to build the core and bench. You can see in the sketch ups below the configuration I came up with.  I positioned the core where it is in order to get the 30 inches recommended clearance between the barrel and the plywood walls. I'll probably still put up a heat shield.


Is there anything you can see wrong with this design? There's some pictures and sketch ups of the heater below, and the sketch up file itself if you want to look closer.  Thanks for your input!

Your layout and reasoning looks good to me, given the constraints you have to work with. The one real change I would suggest is to eliminate the longish bent duct routing, and add another half barrel at right angles to the original set. Cutting the end of a half barrel to fit the side of another is not that big of a deal, and plenty of screws will hold the assembly together securely. Then all you have to do is run a couple feet of duct from the manifold straight into the top of the barrel end, and the exhaust straight out of the bottom of the barrel end to the chimney pipe. (I did this with a 6" demo setup a few years ago, and it worked excellently, drawing well in an unseasonable 90 degree April Earth Day fair.)

In spite of flow advantages, I tend to think it would be better to run the stovepipe straight out the gable wall to a tee and chimney pipe. An angled duct exiting the wall will want to draw rain and condensate back through the wall and inside, while a horizontal penetration needs much less rigorous sealing.

Glenn Herbert wrote:Your layout and reasoning looks good to me, given the constraints you have to work with. The one real change I would suggest is to eliminate the longish bent duct routing, and add another half barrel at right angles to the original set. Cutting the end of a half barrel to fit the side of another is not that big of a deal, and plenty of screws will hold the assembly together securely.

Thanks Glenn.  I thought about adding another half barrel at 90 degrees to the rest, but I wasnt sure if having a turn in the stratification chamber would cause short circuiting of the gasses, or other problems. It's good to hear that someone else has done this with success.  

When running the chimney horizontally out the wall, do you need to provide somewhere for condensation to drain out, or does it just run back down to the clean out at the bottom?

To clarify, I haven't built a multi-angled barrel bell, but I am sure that it wouldn't matter as long as the top is a continuous level. Matt Walker did it for a restaurant some years ago, with more than six barrels, and two right angles if I recall correctly.

I would give the exterior chimney a drain so condensate would not have to come back inside to be handled. I would use a tee and not an elbow at the base of the chimney.

Jesse Grimes wrote:Thanks Glenn.  I thought about adding another half barrel at 90 degrees to the rest, but I wasnt sure if having a turn in the stratification chamber would cause short circuiting of the gasses, or other problems. It's good to hear that someone else has done this with success.

Matt Walker also made a circular bench made from half barrels known as the ring of fire and as far as I know it worked well.

A quote taken from Peter's site bell theory
"It is nothing more than a large enclosed space, meaning 'four walls, a top and bottom'. It can be any shape that works best for the situation, it can be constructed of any material that suits the purpose best, including steel/metal, brick, refractory, stone, clay dug out of the backyard mixed with straw."

Jesse Grimes wrote:When running the chimney horizontally out the wall, do you need to provide somewhere for condensation to drain out, or does it just run back down to the clean out at the bottom?

I have mine running horizontally out of the wall and it doesn't condense enough to matter since it is well insulated. A small drain hole drilled in the bottom could be all you need, however as Glenn mentioned, a tee would still be a good idea since ash can tend to accumulate in this section that would be good to inspect/clean when needed. Again, just make sure its also insulated.

Glenn Herbert wrote:To clarify, I haven't built a multi-angled barrel bell, but I am sure that it wouldn't matter as long as the top is a continuous level. Matt Walker did it for a restaurant some years ago, with more than six barrels, and two right angles if I recall correctly.

I would give the exterior chimney a drain so condensate would not have to come back inside to be handled. I would use a tee and not an elbow at the base of the chimney.

It's not a bell, but a half barrel channel.

http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build?sort=3&page=1



http://donkey32.proboards.com/thread/609/heated-seating-nyc-restaurant