3D Plans - Pebble Style Rocket Mass Heater

Coydon Wallham wrote:

Brittney Gee wrote:Question 1 is, could the bench be essentially doubled in length and function just as well? We are hoping to run a longer bench through a bedroom and into a living room. And, it would actually run under an "empty" wall of tongue & groove separating the two in order to do so... hopefully no issues there?  

And 2: Could the wood feed conceivably be shifted 90 degrees? Ie, be installed to the side of the barrel, rather than the "butt" end?  Or might such a joint there cause issues with draw or else-thing?

Are you specifically looking for a lightweight and/or temporary RMH build? If not, it's likely like you would benefit from a cob style design over this pebble style.

I'd suggest looking over Ernie and Erica's book on RMHs (the rocket mass heater builders guide) before settling on a design. My understanding of the principles spelled out there is that you would be able to to build something to meet your criteria on both points.

If you go with a variation of this pebble style but include a longer bench, I would suggest using an 8" exhaust pipe that is flush with the horizontal ducting. The 6" vertical exhaust going down into the 8" duct for stratification effect used on this iteration seems to limit the draw through the system. Systems this size without the "juice box" design reliably work with much longer runs of ducting through the mass. Specifics on how to calculate those numbers for varied situations are in the E&E RMH book.

Coydon, thank you! I'm grateful for your recommendation. We went ahead and purchased Ernie & Erica's RMH book so as to better understand the dynamics in general. We do not need something temporary/lightweight, and it is my understanding that cob is much more efficient. Thank you for reminding us of this and inspiring us to look back in that direction!

Question 1: On the list of materials it has 1x4 lumber. It seems that the frame is 2x4 and the siding is 1x6, but I can't tell what the 1x4 is used for based on the figures. Is it also used for siding or for something else that I'm missing?

Question 2: Does anyone have a rough estimate on how much pea gravel and sand is needed for this build?

Question 3: I will likely connect this rocket mass heater to a preexisting 8 inch stove chimney. Would it be best to use 8 inch exhaust pipe instead of 6 inch or still use 6 inch exhaust pipe but upsize back to 8 inch where I connect it to the preexisting chimney? If I use an 8 inch exhaust pipe, I would think I'd have to connect it to the end of the 8 inch duct instead of capping the duct and inserting the exhaust pipe via the juice-box style. I'm guessing it would be slightly more efficient with the 6 inch juice-box method even though the majority of the chimney would still be 8 inch.

I'm reviewing these plans and the full movie for the pebble style RMH at the PTJ with an eye to build on the concept. There is a rather large omission toward the end of the project. When it comes to the final fill in of the burn box area and the mass box, there is no mention of details in these plans. It looks like no footage was taken of this process. Perhaps a description of this could yet be requested of the participants to flesh out the plans?

Specifically, I was looking to see how the wall was built to separate the burn box from the mass. We see a couple of courses of bricks being cobbed at the bottom, then some rocks on top of that in the movie. Nothing is shown how the wall is built for full separation to the top of the box. In the plans, step 3F has the partially filled box with no divider going to step 4 where the sections are filled with no indication of the wall being built. This seems like more than an obvious 'build a wall' step because the barrel and manifold extend beyond the base dimensions of where the wall would be, so it is not clear if a curved wall was built, if the wall was cobbed to the sides of the barrel/manifold, or if something else was done.

Also missing is info on how the mass was filled. It can be assumed the pebbles were simply shoveled/poured in to cover the ducts, but this could use explicit description because it seems like any weight now placed on top would work to compress the thin walled ducts and I would like to verify there is no other reinforcement needed for support there...

Coydon Wallham wrote:I'm reviewing these plans and the full movie for the pebble style RMH at the PTJ with an eye to build on the concept. There is a rather large omission toward the end of the project. When it comes to the final fill in of the burn box area and the mass box, there is no mention of details in these plans. It looks like no footage was taken of this process. Perhaps a description of this could yet be requested of the participants to flesh out the plans?

Specifically, I was looking to see how the wall was built to separate the burn box from the mass. We see a couple of courses of bricks being cobbed at the bottom, then some rocks on top of that in the movie. Nothing is shown how the wall is built for full separation to the top of the box. In the plans, step 3F has the partially filled box with no divider going to step 4 where the sections are filled with no indication of the wall being built. This seems like more than an obvious 'build a wall' step because the barrel and manifold extend beyond the base dimensions of where the wall would be, so it is not clear if a curved wall was built, if the wall was cobbed to the sides of the barrel/manifold, or if something else was done.

Also missing is info on how the mass was filled. It can be assumed the pebbles were simply shoveled/poured in to cover the ducts, but this could use explicit description because it seems like any weight now placed on top would work to compress the thin walled ducts and I would like to verify there is no other reinforcement needed for support there...

THanks Coydon, were updating all the plans to be even more precise atm, noting this for the update. Thanks!

Brittney,
Did you build your New Mexico Rocket? The short answer is that no there is no reason you can't co sideways with the feed it just complicates the build. If you still need help I can offer remote consultation (from Cleveland Ohio) or we do come out and do teaching workshop builds.
--Uncle Mud