We have a very primitive open fireplace in a hearth. Primitive in the sense that it's a huge space with a big wide chimney, so it's extremely inefficient. We could have installed a wood stove, but nearly all of us are reluctant to lose the primitive pleasure of watching and feeling live flames and live smoke, and tossing logs onto the fire.
This is what pushed me to look for unorthodox solutions, and how I got to the permies forum and rocket mass heaters.
My current goal
I am hoping to build a kind of masonry heater that will be so slim (one firebrick deep) that it will leave enough space, if placed against the back wall of the fireplace, to have a small open wood fire right in front of it. In an ideal situation, we'd be able to have both running at the same time.
Here is what I've built so far.
If it isn't immediately obvious what you're looking at: the firewood goes in the black square hole at the bottom. The fire tunnel goes towards the back wall, then the chimney leads up to nearly the top of the brick mass, and the the air is led to the right (about one brick's length); then all the way down to nearly the floor; then briefly right again, and then all the way up. Until it exits where the two bricks kind of stick out from the mass.
The problem so far
Now I've given it a brief try, and it is not working as well as I had hoped. The fire does go horizontally into the burn tunnel, and the air does come out where it's supposed to. But...
* some smoke is exiting between the bricks. I'm in test mode, without mortar, so that is not strange, especially as the firebricks turned out to be not quite 1:2:4 in depth-width-height. So there are tiny gaps.
* the air coming out at the desired point is often very smoky.
* the burn tunnel and the chimney mostly do not produce the rockety sound.
My questions / theories
So I wonder if these four things could be the cause and/or the solution...
a) Add mortar. The chimney will be airtight and make the rocket effect work. Which will improve combustion and draft at the same time.
b) Add length. As you can see the chimney is just under three firebricks tall. Maybe that's not enough? I have more vertical space I can use.
c) Increase diameter. The air tunnel is only half a brick wide (and deep). Most examples I've seen are wider.
d) Don't channel the air all the way back down. Maybe it's asking too much to push the air all the way back down to the floor before letting it go up.
All of the above? Anything else? I'd love to hear comments.
PS: Rocket mass heaters excite me a lot, but the setup with a heat riser surrounded by a full-size oil barrel is just too large to fit in this hearth.
Well, i've thought about the same problem before. One trick could be to use a petrol or fuel tank of some kind. A home heating fuel tank, or one for storing fuel for tractors. I'm thinking of the rectangular type. Instead of the barrel. A good idea if you like seing the fire would be to use an horizontal batch box rocket. http://donkey32.proboards.com/thread/511/adventures-horizontal-feed you have some refractory bricks. Instead of a barrel, you could make some kind of shuttering inside the chimney itself to form a bell. Then either you come back down for a solid mass, or make a second bell.
If you want, i could give more advice, if you take pics from further away, so we can see the whole pic. An inside pic looking up the chimney would be good as well as dimensions.
For less money than almost any other possible modification of your existing fireplace you will easily add 30% more heat out into your room, slightly more so if you have a ash pit
clean out leading to the basement area !
Outside of a possible upgrade to the shaping and condition of your fireplace chimneys smoke shelf you may even find that you now have more room to consider for the co-location
of a rocket mass heater with separate "new'' exhaust Chimney ! Hope this helps !
For the Good of the Craft ! Think like Fire, Flow like a gas, Don't be the Marshmallow ! As Always, your comments and Questions are solicited and welcome ! BIG AL
As for alternatives to the upside down oil barrel, I think I'll just go with the masonry heater concept here, and try the rocket setup in the basement.
@Allen, thanks for the Rumford tip. You read my mind there: I was aiming for the masonry to bep the back wall of a Rumford shape fireplace. Funny detail: when I did a google search for the keywords you mentioned, the first and only hit was your message in this forum. But I get the point.
And and air inlet from the basement is also in my plans. I actually want to add a fireplace grill that heats air and spews it horizontally into the room.
Wytze Schouten wrote:@Max, thanks for your comments. When you say to isolate the burn tunnel and heat riser, I assume you mean more than just fill the gaps. But why add more isolation when it's already surrounded by solid brick at least 3 inches thick?.
Well, is brick insulative? Nope! The trick behind a rocket of any kind is not the shape of the burn tunel, but the insulation surounding it and the heat riser, The insulation keeps the heat, and therefor burns the last burns all the hydrocarbons in the gasses. Frankly, with little effort and creativity, your hearth can become a huge massonry rocket heater.
Prety sure you could do something along thoses lines inside it.
http://technologieforum.forumatic.com/viewtopic.php?f=19&t=27 Make the bell in the funnel part of teh chimney. With just a place to the side to get the tubing for the flue out.
ernieanderica.info, with a little more information to allow you to ask well thought out questions, I am sure that Ernie or Erica Wisner Will get back to you with more
Due to the heating characteristics and the feeding requirements of Rocket Mass Heaters R.M.H.s, attempting to run the Heater from a remote location is doomed to failure,
if you are not willing to consider it as the Keystone and linchpin of a Home entertainment area, and give it 'pride of place' you will not be satisfied with a R.M.H. for any thing
but emergency back up heat !
All of the Questions you have asked 'Max' are explained in detail in Ianto Evans' Great book Rocket Mass Heaters, you can get a PDF Copy $15.oo U.S.D. from
cobcottage.com, There is STILL no other book in any language* that has more rocket stove / Rocket Mass Heater family information ! ( and I don't make a dime ! )
For the Good of the Craft ! Think like fire, flow like Gas, Don't be the Marshmallow ! As always, you comments and questions are solicited and are Welcome ! big Al
* There are condensed copies of Rocket Mass Heaters out there in Spanish, French, and ? for people who comprehend better in their native tongue !
For safeties sake, do all your practice builds out doors before attempting to install your wood heater indoors ! You Can use a smaller barrel ! A.L.