• Post Reply Bookmark Topic Watch Topic
  • New Topic
permaculture forums growies critters building homesteading energy monies living kitchen purity ungarbage community wilderness fiber arts art permaculture artisans regional education experiences global resources the cider press projects digital market permies.com all forums
this forum made possible by our volunteer staff, including ...
master stewards:
  • Nicole Alderman
  • raven ranson
  • paul wheaton
  • Jocelyn Campbell
  • Julia Winter
stewards:
  • Burra Maluca
  • Devaka Cooray
  • Bill Erickson
garden masters:
  • Joylynn Hardesty
  • Bryant RedHawk
  • Mike Jay
gardeners:
  • Joseph Lofthouse
  • Dan Boone
  • Daron Williams

RMH design comparison  RSS feed

 
pollinator
Posts: 268
21
books chicken hugelkultur solar tiny house urban
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Along the same lines of this thread, I've seen many different designs of rocket mass heaters, but have no real frame of reference to what the benefits are of one over another.

I realize that it's not always a linear scale from good to better, but that the design is based on unique factors of each build--It needs to withstand higher-than-normal temperatures, it needs to be portable, it needs to have a certain aesthetic, etc.

I've seen RMHs with the following various design traits:
square shaped heat risers made of brick
round heat risers made of a smaller and larger metal pipe, with the space between them packed with various substances
round heat risers made of durablanket and mortar
burn tunnels made of brick
burn tunnels made of duraboard
burn tunnels with holes on each side (for a heat riser and a feed tube) cast out of some sort of cement

The same applies to the bell/barrel, as well as the mass.

I imagine there are hundreds of thousands of variations in the shapes, sizes, and materials used in RMH builds, I'm not looking for an exhaustive comparison of all possible combinations, just a general frame of reference into what goes into the thinking of the designs and how I can know how to decide, and what factors those decisions are based on.

Maybe something like a cost/benefit analysis, or a comparison in the tradeoffs between one material over another.

 
gardener
Posts: 2581
Location: Upstate NY, zone 5
92
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
Okay, for starters...
Brick gives a modular layout that can be readily repeated (correctly) by someone with minimal skills. It is very durable and a broken brick (there is one location in a J-tube which gets the hardest wear) can easily be replaced.
Ordinary firebrick has a lot of mass which reduces the efficiency of the combustion a bit. It must have significant insulation around it. Its modular nature resists certain subtle design tweaks which improve efficiency.

Castable refractory cement can be formed to any precise shape desired, to get the most efficient combustion possible. It can be made to the exact thickness desired, and dense inner material can be bonded to insulating outer material.
It is generally less durable than brick, and if it breaks it can be difficult to replace a section. Broken-out areas can be patched roughly if they are accessible. It requires skill to correctly make the form and cast the material.

Both firebrick and castable refractory tend to be expensive; prices vary considerably by region for different materials, and it is sometimes possible to find a super deal on a particular material. Bricks can be salvaged and reused, while castable cannot.
 
Paper beats rock. Scissors beats tiny ad.
What would you cook first in a rocket oven?
https://permies.com/t/89866/cook-rocket-oven
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!