Hi, new to the forum, and I'm interested in building a rocket mass heater.
I have a very large timber-framed room (very high ceiling/lofts). This room has a very
large central fireplace, open on two sides. I have a nice Englander WS on one side, but
would like to have a RMH on the other. The stonework on the firelplace is very large, and,
of course, the chimney is freestanding, probably close to 20' tall, not connected to any
exterior wall. So, to my question, I want to take advantage of all the thermal mass of the
stonework on the fireplace, and would like to transfer as much heat into it to "charge" it as
I can. While my description makes it sound like I have a majestic expensive house, the truth
is that it is an almost 40 years old DIY one built by two friends and looses nearly all of it's
daytime thermal gain to drafts and losses through the tremendous amount of glass surface area
of old-time single and double pane windows (and it takes 4-6 cords a winter to heat, and even
then not very well...). Anyway, now to my question. Most RMH efforts are geared to very well
insulated, self-contained heaters. My intent is to transfer all the BTUs I can to the existing FP.
I understand that concrete block and sand are not ideal insulators - can I utilize this to my
advantage in this case? The problem is, of course, that I want to direct these "losses" along a path,
while still keeping all other surface areas from robbing my efforts of charging the existing FP. I
was probably going to use an 8" square steel intake, welded to a 9" dia. insulated chimney,
(very similar cross-sectional areas), so, I wasn't having cement blocks exposed directly to the flames.
(Also, my neighbor has some lengths of 8" sq chimney tile - would that be better for the burn chamber?)
One thing that I was wanting to do was build up a semicircle of brick or rock/cob around the barrel,
full height, about 3" away from it to try to draw off some of the higher levels of radiant heat into the
thermal mass, but I wonder if this will alter the swirling path inside the barrel because of the temp
difference from one side to the other. Also, I'm sure that will direct the remaining radiant heat more
narrowly, though I don't see a downside there. On the cob - I've checked my local soil survey, and most
of soils listed are described as clayey, but I've never really noticed anything clayey when I dig...Can
I use it anyway, or should I buy it? (Trying to do this on the cheap, as I was out of work for nearly
1 1/2 years until recently, and now my wife is also). Also, another question is the distance from the top
of chimney to the barrel, typically I've always seen 1 1/2", but lately I've been seeing 2" occaisionally.
Is that for the larger stoves, or is it tied to the cross-sectional area somehow? And would it be necessary
to put another layer of steel at the top of the barrel so that it doesn't burn through with those super high
temps? One more question - I had intended to run 8" dia ductwork for the exhaust under the barrel for the
rest of the way, but will that be too much of a drop in cross-sectional area, (from .442 to .349)? And, even
if I decreased the burn chamber and chimney size to match this, how do you get around having to neck down the
exhaust hole under the barrel? If you center the chimney, you don't have room for a 8" dia hole. I imagine
most people compress the duct and make an ellipse, but you start losing area quickly when you do that. Anyway,
if anyone has any thoughts or ideas on how I can achieve this kind of derivation successfully, I would sure
like to hear it. This seems like a great forum with some very informed members. Thanks!
Paully, A picture of your house would help and how you want to run the ducts. My landlord has a 2 story house and wants to run the ducts upward side to side at 45 degrees instead of horizontal on the ground. He wants to run the ducts inside of a cob/stone wall up into the second story. I told him I think it would work with the only problem being how to cover the ducts with cob and a stone facing. Also it would exhaust much quicker than on the ground. Alan
Pauly Bart : Add my voice to pictures, sketches, videos ! We want to catch cold air as it enters and falls into the room, and onto the floor, it will certainly be possible to add
ether a shed like entrance chamber or an inside 'Mud room' below the grade of the rest of the house. You still lose heat when you open an outside door, but you don't get
major drafts and the cold air has somewhere to settle, a passive cooling 2 for 1 win win !
You are having a small problem in visualizing the thermal mass, and how it works, back to that in a few words !
The Rocket Burner itself, in its best possible modification from its ~25~ ish year history is reaching new and freakishly high temps, and doing so in fractions of the old bench-
marks! Here super refractory insulative materials instead of soaking up the heat re-radiate it into the Burn Tunnel / Combustion Chamber, with new higher temps that will puddle
glass, as anew member you are understandably concerned about barrel longevity back to that in some more words !
The rocket mass heater gets its valued high efficiencies, from the heat that is stored within the Thermal Mass, with out this 'Storage Battery' for the Rocket Burners heat energy
output the Rocket would only be a curiosity as most of the heat energy would then leave the house as exhaust gases,up the vertical chimney just like a conventional' wood stove'!
Because we use Cob and lots of Dense materials like (heavy) Rocks, with the ability to absorb most of the heat energy from the hot exhaust gases within the horizontal chimney,
we are creating a heat storage device that re-radiates the stored energy at a human comfortable temperature !
From the time it leaves the barrel we only want the hot exhaust gases exposed to super absorbers, not super insulators as you stated in your post, remember, in order to re-
radiate it we must absorb it first and want dense non-insulative materials !
Many years ago I took shop/industrial arts so I would not have to do Chemistry, as a result I forget which elements are cations and which are Anions- With in the barrel it seems
that the Carbon, Oxygen, and Hydrogen have a mass affinity for each other, to the exclusion of Fe or Iron and steel, which lies protected behind the zone known as the Laminar
flow (areas) and probably should for the purposes of understanding here- be called the laminar non-flow zone/areas !
If my experience proves any thing, trying to wield on this material, seems to show that the Iron does combine with some Carbon if the number of 'sparks' mean any thing !
Most of the original 55 gallon barrels used in rockets stoves for the last 20 years are still inservice, and if replaced it was do to an excess of caution on the part of the owners !
The standard guarantee for the heat exchangers on a Commercial Fossil Fuel fired Forced-Air Furnace (and that is what you are using the barrel for, a Heat Exchanger) is 20 yrs
They guarantee them for 20 years because nearly ALL of them will make it ! and the commercial heat exchangers are made out of lighter materials !
This is a starter to your asked and unasked questions, please sent us pictures, you have some 19,00 members who want to understand where you 'are coming from' and have
ideas of their own to share ! Hope this helps and is timely, For the good of the Crafts !
Think like fire, Flow like a Gas, Don't be the Marshmallow! As always, your comments and questions, are solicited and Welcome ! PYRO - Magically BIG AL !
Success has a Thousand Fathers , Failure is an Orphan