RMH build summer 2021

Hi, just writing to show a rocket mass heater i built, following generally the Minnie by Peter Van den Berg and a little skimming of the RMH book by Ernie and Erica.

Any comments would be helpful as this is a first attempt with virtually now previous knowledge. I’ve probably made some mistakes, but i’m writing this sitting next to the working model, so i suppose not too much got bungled. Had a problem with the riser and it got a little too wide. Also put stone on top, which could expand and blow the whole thing up in a few minutes here, so we’ll see. I lined a cement dog house with fire brick and learned later it was reinforced and had metal inside. Oops. And the masonry work is shoddy, but I’ve never done that before. Here are some pics.
William

Finished product:

Hi William,   That's a great start! Building a RMH can teach you so much about what works and what doesn't that can't be replaced by book knowledge alone.

I have several questions about your photos.

1) Is the exhaust chimney outside insulated or single wall pipe? It would be best if it was insulated to help keep temperatures high enough to encourage good draft and also to help keep excess condensation from forming.
2) Is your bench a bell (hollow chamber) or is it a pipe run?
3) What are the dimensions of your heat riser? It looks really big to me from the photos. Overall dimensions also look off to me. Was your dog house the right size as a form to produce the necessary final dimensions for the core?
4) Is the heat riser insulated? This is the key place where high temperatures are needed to help burn up the wood gasses and produce a clean burn.
5) Can't exactly tell how the flow of gasses proceed beyond the top of the heat riser. Do they travel all around that brick mass or between the firebrick heat riser and metal shell?
6) The stone on top may very well crack and crumble from the intense expansion/contraction experienced over the heat riser if not protected with some insulation.

Hi Gerry. Thanks for the reply.
1) exhaust chimney not insulated. i could lokk into that.
2) the bench and “volcano slope” are just cob and old clay bricks. No pipes/no manifold. They don’t seem to collect much heat which is unfortunate.
3) i think internally the heat riser is about 30cm. I realized too late it was too big but the firebrick slabs didn’t really fit together well and i learned later how easy cutting brick is.
4) heat riser is insulated with perlite and surrounded by galvanized sheet roofing pounded out flat.
5) fire tunnel il 60 cm and 17cm tall. I built an extra front-piece to get the wood loading thing up higher to make a “J”. The gasses go up above the heat riser hmthen come down around the bricks and then 15 cm from the bottom they enter the exhaust pipe, so the outside temp reading around the inlet is lower than it would be up higher.
6) so far stone lid is ok. Went up to @ 90 celsius today. We’ll see.
Thanks again.

Gerry Parent wrote:
1) Is the exhaust chimney outside insulated or single wall pipe?
2) Is your bench a bell (hollow chamber) or is it a pipe run?
3) What are the dimensions of your heat riser? It looks really big to me from the photos. Overall dimensions also look off to me. Was your dog house the right size as a form to produce the necessary final dimensions for the core?
4) Is the heat riser insulated? This is the key place where high temperatures are needed to help burn up the wood gasses and produce a clean burn.
5) Can't exactly tell how the flow of gasses proceed beyond the top of the heat riser. Do they travel all around that brick mass or between the firebrick heat riser and metal shell?
6) The stone on top may very well crack and crumble from the intense expansion/contraction experienced over the heat riser if not protected with some insulation.

As you may know William, you could also forget about cutting all those firebricks and instead with the addition of an internal form, make a perlite/clay heat riser instead.  The less mass you have in the core/ heat riser, the faster the fire can get up to temperature.
Just curious why you didn't utilize the bench you made as a thermal mass heat storage area?

Gerry: I Didn’t use the bench as a thermal mass storage because
A) that would have required a manifold, something I’m hesitant to build since it seems beyond my capabilities.
B) I thought wrongly that it might store some heat anyway.
C) the bricks around the insulated heat riser and the stone on the top hold heat.
D) This is a small little room where we make morning coffee or will go to when it’s cold and we’re working outside, so not much need for prolonged heat, although i made a fire at noon and at 7pm the room was still comfortably warm.
William

I can guarantee you William that building a manifold is not beyond your capabilities. The manifold is nothing more than a transition area for the hot gasses that have left the core to be delivered to the mass.
Just don't make it too small or have any sharp angles and you should be all right.

Flue-exhaust-transition-plenum-pictures

If your good with what you have, then no problems, but a half barrel bench with a relatively thin coat of mud over it would provide quick heat and go quite well with a morning cup of joe.

Buon giorno, William.

Dove in Itaia Nord?

Ciao

Russ

Russell Harper II wrote:Buon giorno, William.

Dove in Itaia Nord?

Ciao

Russ

Welcome to Permies Russell. Care to introduce yourself in https://permies.com/f/68/introductions ?

If you do I can add your post to the regional forum for Europe as well: https://permies.com/f/32/europe