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Rocket Mass Heater Plans: Annex 6" L-shaped Bench by Ernie and Erica
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pebble style rmh - in the fisher price house

 
steward
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I bought 200 raw acres and then a little house and shop about a mile away. In time the raw land was called "the lab" and the property with the house and shop was called "basecamp".

Basecamp came with the shop (sometimes called "the auditorium), a tack room (now called "the little red cabin"), a sort of garage/storage building (now, the office and the garage) and a tiny double wide house (the fisher price house - named because it is one big gob of plastic).

In october of 2013 we built a pebble style rocket mass heater in the house (based on some designs I came up with in 2010). A beautiful wood box, granite slabs on the top, and stainless steel barrel. Very pretty. Only it worked poorly.

This january, ernie and erica came by and after an hour or two of debate we came up with a design to route the exhaust out the roof instead of the wall. We decided on a design that would sacrifice efficiency for rockety-ness and best chance of working okay with newbies. The new design worked amazingly well. Freakishly well. Too well. The whole thing got too hot! Ernie reduced the size of the wood feed and erica added length to the ducting.

In january, all of the rocks and pea gravel were sitting outside with lots of snow and ice on them. We decided to wait until july or august to finish the project - so that we would be bringing in dry pea gravel and rock.

June is supposed to be one long rain storm that never happened. So during the PDC it was all plenty dry and the student brought the rocks and pea gravel in.

Morgan Bowen was here and made this video:




 
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Thanks for that! It's cool to see the hams/prosciutto curing in the background.

Here's hoping for at least one cold(ish) night so we can see how the thing works when we're there in late July. (Yeah, not likely.) It looks marvelous.

The area in front of the house looks so different now that there are giant hugelkultur berms!
 
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Hi folks,

hereĀ“s another up-to-date and very informative video about this rocket mass heater.
Discovered it just now on Youtube. Enjoy !


 
paul wheaton
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Here is a clip from the "better wood heat" 4-dvd set:

 
paul wheaton
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Here are some pictures that sara took of the fisher price house:





 
paul wheaton
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Another little video about this rocket mass heater:



 
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Paul, did you need to provide any extra support under that RMH?  We are buying an old farmhouse in Kentucky.  The current heat source is a wall-mounted propane unit, which I really don't want to use; there is a chimney in the center of the house that hasn't been used for many years (at least thirty years, according to the realtor, who lived in the house at one time).  Obviously the chimney needs an inspection and possibly some repairs, though the exterior looks solid, before we can use it.  But I would sure like to be able to use a RMH in there instead of a 'normal' wood stove.  Just wondering if we'd need to get underneath and provide extra floor support, or possibly even cut out part of the existing floor and build a foundation on the ground under the house?

Kathleen
 
paul wheaton
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Take a look at the trailer for the "Better Wood Heat" dvds:



We show the full build of the pebble style rocket mass heater in the dvds.   And in the trailer, if you look at about 1:50 it says something about how it included building on a conventional wooden floor - and you can see somebody under the house to put the extra support in there.
 
Kathleen Sanderson
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paul wheaton wrote:Take a look at the trailer for the "Better Wood Heat" dvds:



We show the full build of the pebble style rocket mass heater in the dvds.   And in the trailer, if you look at about 1:50 it says something about how it included building on a conventional wooden floor - and you can see somebody under the house to put the extra support in there.



Thanks!  (One of these days I'm going to get the DVD set, but don't have them yet.)

Kathleen
 
paul wheaton
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Kathleen Sanderson wrote:  (One of these days I'm going to get the DVD set, but don't have them yet.)



You might want to check out how cheap the 4-dvd set is right now:  richsoil.com/wood-heat.jsp



 
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Just wondering, if I buy the dual 4 pack dvds in the hd streaming version, can I permanently download them onto a laptop? We are broke, but want to build a rmh for our place. We have solar, no internet, but can download from a library 20 miles away, so streaming doesn't work unless I can download & keep the entire dve.
 
paul wheaton
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You want to get the tiny download version.
 
paul wheaton
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A few winters ago, we were able to heat this home pretty comfortably with 0.60 cords of wood.   I think we can do better.  Maybe in two years we can do this test again and possibly get down to 0.20 cords of wood.


Improvements to the RMH

  - switch to a mild steel barrel (conducts heat better - so more fast heat)
            (the stainless steel barrel is too pretty)


  - convert vertical exhaust from 8 inch to 6 inch (slow heat loss when not actively burning)

  - convert the existing 8 inch duct in the system to be  more of a stratification chamber

          o make a path for the duct to be at the bottom (currently, it is staggered)
          o add a place for hot gasses to rise into a dead end
          o add a juice box stratification to the end of the run

  - build a "cap" to go over the two bricks at the wood feed for when there is no fire.  It will reduce the amount of air entering the system when the fire is out.


Improvements to the house

  - insulating insulated shades plus window quilts on all the windows

  - enclosed front porch

  - micro heaters for where people spend time, thus allowing the overall temp in the house to be cooler

          o maybe move kitchen lights lower


Improvements to the techniques

  - burn more waste paper and cardboard

          o during the last test we used water paper as fire starter, but let's expand this

          o perhaps the whole test will end with "we heated a 3-bedroom home, all winter, on junk mail and amazon boxes."

          o maybe even encourage heating the house up to 80 once in a while using strictly cardboard

  - set up air cleaners and dehumidifiers throughout the house

          o rather than sucking air outside so often, let's see if we can keep more inside

  - lets get some data on the temperatures for homes that use wood heat and see how cold they get in the mornings

          o in our previous test, the coldest we allowed was 66 degrees.  If other homes allow it to get colder than that at night, maybe we will do something similar

          o maybe lean more on micro heaters



This is two years out, so this is a good time to come up with a lot of possible ideas and move in that general direction.   Any more suggestions?

 
paul wheaton
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here's a pic somebody took and posted on wikipedia:

 
paul wheaton
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I updated the post (two posts up) that has ideas for optimizing the system.  I added a few things that I've thought of the last few months.  The big one from today was

build a "cap" to go over the two bricks at the wood feed for when there is no fire.  It will reduce the amount of air entering the system when the fire is out.



This would improve the efficiency of the system when the fire is not burning.  It is possible that this one thing could take the test from 0.60 cords of wood to 0.50.

 
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