Gerald Gobb

Pete Acker wrote:Hi All,

I have recently bought a house with a brick fireplace and chimney that was never used, and I want to build a more efficient way to garner some wood heat that will fit on the hearth and in the fireplace. I've researched like crazy on RMH's and masonry heaters, but haven't seen any fireplace adaptations that I like, yet. So, I've been kicking around ideas in my head to design my own, based on a cast J-core and modified from there. Here is what I've come up with (cross section attached, looking straight at the fireplace, with the flue exiting out the back and up the chimney). I'd like to cast the entire structure, probably out of blocks of fireclay/perlite/fire cement. I know you all are the experts, so I've come to you for assistance and comments. First, do you think this concept would work? Would making it out of that material work? How thick should the walls be?

Any other comments would be helpful. I'm not interested in a barrel and typical RMH at this point, and I don't have the masonry expertise or money to afford a proper masonry heater. Thanks in advance for your time,

Pete[/quote
may work but not well 1. perlite is an insolation that will keep the heat in the stove tell it's up the chimney. would ok in the first chamber
2. move the flue pipe to the down to the floor of the 2nd chamber and make the chamber of cob (clay& sand).

how large is the yerd that they are in?
you will find that when they are in a small area this will be more of a problem but once started the only way to stop it is to eat the pecking chicken the bast yard size is about .5 square yards per chicken .5 square meter.

thomas rubino wrote:Hi Scott; Your mock build looks good, Ash build up with an open system is normal, when you cover your heat riser with the barrel your burn temps will quickly rise increasing heat thru the whole system creating a secondary burn that should incinerate almost all but the finest fly ash. Your heavy bricks should be used in your feed tube and burn tunnel and the lighter bricks would go for your heat riser. Dwell time translates to back drafting ,not good. 5" is more gap than you want at the top of the heat riser , experiment, but 2.5" is normally what is used. You want the turbulence created by the close tolerance to get the secondary burn going as well as the heat pump effect of cooling air sinking down and pulling more hot air up the riser and therefore pushing more heat where you want it.

The 5" gap will be good here has been stated in a lot of the rocket stove books and forums a formula rhat takes into account the area of the gas flow but not the laminar flow of the gases.


For example, an 8 inch system via Pi R2 will give you 50 square inch, the circumference is Pi D, a little bit more than 25 inches. Fifty inches divided by 25 inches is exactly 2 inches for the gap between end riser and the top of the barrel. Mark however, this is the minimum size for such a system according to the book,

The same method goes for a square heat riser, by the way

This example has no compensation FOR LAMINAR flow steam leaving a pipe. It will act the same for a short distance just out side as if the pipe were the pipe extended do to laminar flow on an 8 inch system a 2" gap will be undersized at low pressure ( under 10psi ) the laminar effect will be about 2% of the area For the 8" Pi * R*r / Pi *D + (.02*pi*R*R) 50/25+.02*50=3 for the minimum gap.
I have seen an 8" running into 2 55 Gal. drums stacked 1 above the other with no bench 10" of [pipe @ the floor 5' up 24 " into a brick chimney.

Gerald Gobb wrote:

Ted Visner wrote:I just finished building my MRH and it doesn't draft???

I am uploading pictures to show.

Does the horizontal burn chamber need to be the same size as the vertical?

Ted
Looking at your stove I see two things that may help you
1 at looks like your drum may be too low the info that I find calls for a 2 inch gap on a 8" system but the formula is not looking at the laminar effect of the gasses leaving the riser and a factor of 4 or 5% of the diameter has to be added making the min. gap 3 inches " higher is better.
2 in your pictures the exit port looks about the same size as the CSA of the rocket making a bottle neck try moving the exit port out from the center about 10 or 12 Inches and rearrange the brick work into a funnel shape as the gasses coming down in the drum have to rap around at the base of the drum turn then move side around to the exit where the 2 streams run into one small area where they must turn to exit adding a drag in the system by funneling the exit you remove a lot of the drag.

Regards Gerald

PS remove the styrofoam from under the stove will not stand up to the heat and will catch fire please use vermiculite insulation board.

Ted Visner wrote:I just finished building my MRH and it doesn't draft???

I am uploading pictures to show.

Does the horizontal burn chamber need to be the same size as the vertical?

Ted
Looking at your stove I see two things that may help you
1 at looks like your drum may be too low the info that I find calls for a 2 inch gap on a 8" system but the formula is not looking at the laminar effect of the gasses leaving the riser and a factor of 4 or 5% of the diameter has to be added making the min. gap 3 inches " higher is better.
2 in your pictures the exit port looks about the same size as the CSA of the rocket making a bottle neck try moving the exit port out from the center about 10 or 12 Inches and rearrange the brick work into a funnel shape as the gasses coming down in the drum have to rap around at the base of the drum turn then move side around to the exit where the 2 streams run into one small area where they must turn to exit adding a drag in the system by funneling the exit you remove a lot of the drag.

Regards Gerald