Rick Lawrence

I had a thought and wondered if any of you have ever tried this> My thought was to add a fan in the outlet pipe ( L ) to suck air through the system and start the draw even with no fire. or put it on ( A ) the intake to blow air on the fire? I think that putting it on the exhaust would work best but just a idea at this point. I'm still looking for some material to build my first test stove to try out some of my ideas.

allen lumley wrote:Rick Lawrence :I find that I like your idea a lot,

I hope you have a little more extra slop in your 10 inch pipe then is shown in your sketch, or can trim a little thinner, Your Firebrick will expand ! Some room for
expansion must be allowed for !

Hey Allen,
AKA Big Al
Do you think that firebrick expands more then steel when hot? They will both expand some I know and for the most part, the steel will be at a lower working temperature than the firebrick will be so I'm not really sure how it will effect it. I may modify my idea to use thinner firebrick as somebody suggested and more insulation on the outside to cushion the brick as it expands.

Arlyn Gale wrote:Allen - yes, the staggered mortar joint makes the alternate courses interesting. A square outside/octagon inside, such as PvdB documents, addresses that issue.

I like the layout of this but I had the idea to swirl the gas up the heat riser tube like this. Not a real good drawing I know, but hope you get the idea. I would still use a steel feed tube, (as in my other sketch) and a octagon firebrick heat riser.

allen lumley wrote:

Late note : Rick, while probably not idea you can create an interesting spiral to stagger your mortar joint lines, this will increase turbulence and may or may not help
complete combustion ! A.L.

I wasn't planing to mortar the joints at all in this section as the pipe will hold it all together tightly and with insulation packed into any dead space there would be to way for it to expand, unless the pipe failed. As I understand it, the heat on the outside of the heatriser is far lower then up the middle. So a heavy walled pipe should hold up fine.

Arlyn Gale wrote:[quote=Rick Lawrence "Did you read my post at all? Like it says 2" firebrick cut at 22 1/2 degrees 3 7/8" long."

If you cut 2" bricks per your diagram, they won't fit in a 10" pipe without further trimming, and, perhaps more importantly, will only give you a 5-3/8" (inside) octagon.

[/b]For a 6" (inside) octagon, 2" brick should be cut (@22.5*) 4-1/8"(long) [/b]. The outer octagon would be 10".

My figures are correct and you made a mistake in using a 10" octagon not a 10" circle, as they are not the same thing. A 10" diameter circle you could only fit a 9 1/4" octagon into. The circumference of a 10" circle is 31.42" and the circumference of a 10" octagon is 33". Standard firebrick is 9" long 4 1/2" wide and 2" thick, cut the 4 1/2" at 22 1/2 degrees to 3 13/16" for a loose fit or 3 7/8" for a tight fit.

allen lumley wrote:Speaking as an old cheapskate, I have no problems with building an RMH with what comes to hand, Ideally the floor of the combustion core should have
some hard dense fire brick for durability,and a case can be made for including them in the heat riser to promote a good strong draft and easy relighting

Having said that the less mass to absorb the heat the more of the heat energy that will be reflected back into the combustion zone, the quicker it will come
up to temperature and the Cleaner the total burn will be!

Would it be better to use the soft firebrick for the heat riser tube or the hard stuff. I was planing to use the hard for the combustion chamber but not sure which would work best in the riser and hold up the longest.

Arlyn Gale wrote:According to my new friend - http://www.pagetutor.com/octagon_layout/ , you'd have to trim the outside tips of 2" brick a bit to fit into a 10" pipe. (Perfect cuts would require a minimum 10.75" ID pipe with untrimmed 2" bricks). From everything I've read, metal should hold up OK on the outside of the heat riser.

Did you read my post at all? Like it says 2" firebrick cut at 22 1/2 degrees 3 7/8" long.

Here is a design I came up with for a heat riser tube made from firebrick stacked inside a 10" pipe.
Will this hold up to a rocket stoves heat for a extended period of time and what could I do to improve it.

Tnx Al for the info
I went to Rocketstoves.com and looked at the info and will get the download when i get a few extra bucks.
The house is currently about 750 sq ft and will be 1500 when done. the current part of the house is on a foundation with a half basement. The addition will be post and pier with a 2 to 3 ft crawl space. There is a wall behind the stove, but it will not be load bearing to any real degree. The house will be 42 X 36 when complete.
I didnt think that a wood fire could reach 3000 degrees so I can see why steel would fail at that kind of temps. so I will change my plans to firebrick and cement or cob if I can figure out how to get the clay and how to make it.
I had another thought on the wood supply tube that might solve the trapped hot gas you talked about. Take a look at this and add comments





Basically the feed tube will act like it is only about a foot tall as the air is coming in at that point. The burn chamber will be 2 feet long and the heat riser tube 3 ft long for a
1, 2, 3, ratio that's what I have heard is the best. I also added a small hole to the cap on top so it will suck a small amount of air in and keep it gas free.
The reason the mass air duct (J) is larger is to slow the air down it this section to allow more time for it to transfer heat. I got this from a guy that built a working RMH and he said it worked well, he also had a smaller combustion tube (D) to speed up the air at that point.

If I use fire brick to make the heat riser tube does it still need to be insulated? can the firebrick be mortared together with cob or mortar mix?

How hot is cob good to and what does it do when it gets overheated?

Ok, tnx to all that have replied to my post. First off here is my addition plans. The new rocket stove is as close to the center of the completed house as I can get it and keep my floor plan.
The addition is going to double the current house size. so everything above the red line will be new.



Second I don't understand why heavy walled steel tube would fail, when I see tons of rocket stoves made from basic stove pipe on the net?
I'm talking about 3/8 " wall steel here. Even at 1000 deg it will still hold up fine. I've been a welder and steel fabricator all my live so i have some knowledge of steel melting points and such. Granted I have never built a rocket stove so I don't claim to know it all, just trying to understand the whys. I want a stove that will burn for at least 8 hours that's why the long feed tube so I can stick a larger amount of wood in it and it would gravity feed into the burn chamber. I do not want to just sit and tend a fire all day just to keep the house warm. Somebody must have figured out how to do this. I have read a lot and I see a lot of different ideas on the best way to build a rocket mass stove and I'm hoping to find a happy medium. I do plan to build some small test stoves to work out some of my ideas over the rest of the winter to see what works and what doesn't.
One last thing I don't have any source of natural clay here that is why I was doing to use the concrete and I want to make it all look like river rock when done.