VICTORY ( New Design )

[larsmith]

Well, ladies and gents, I've finally "finished" my heater.
It's based on the Rocket Mass Heater but doesn't use the 55 gallon drum.
You can view it by clicking on the link below :

www.youtube.com/watch?v=-jzKKIHhTU0

The opening into which I put the wood is the size of one of the bricks ... 4.5" by 9"

The wals are a full 4.5" thick.

The Burn Tunnel and Heat Riser are same size as the intake.

I've built a down-draft exhaust on the back of the heater such that the air goes in the normal way, up thru the heat riser, across the top of the heater ( over-sized opening for ease of flow / transition downward ) and the down the back of the "J" to the floor, thru an 8" 90 degree elbow, thru a 2' 8" pipe, another 90 degree elbow, thru an 8" 'T' which I've capped and will use as a cleanout, thru a 2' 8" pipe which goes underground under the wall of my heater room, into a 'T' and then up thru my 8" chimney.

So far, the highest temperature I've had indicated on my magnetic thermometer ( commonly used on wood-stove chimneys, etc ) has been around 220 ( supposing that the unit is anywhere near accurate ). I've put a big fan next to the heater to drive heat into the main part of my home and that surface temp is running around 200 now.

I've not yet tested the exhaust temps but the black cap I've put on the exhaust 'T' at floor level runs about the same as the temp at the top of my heater.

Check out the video and you'll see the thermometer @ the top of the heater.

The heater is rather non-descript ... nothing to write home about, as they might say ... but it works well. We've already noted a drop in usage of our Monitor kerosene heater ( actually a ToyoStove but figured you'd recognize the name Monitor ... they're both direct-vent heaters and rather efficient ).

There's approximately 180 bricks in the body of the unit at a cost of one dollar a brick. There's 10 bricks per layer and 16 layers to the main body of the heater.

The unit exhausts thru an 8" pipe which I've encased in cobb. I've plans to add to the amount of cobb and then to back fill the rest of the floor with sand. The floor is presently sand only and will probably remain that way, tho I may place sidewalk pavers or perhaps red brick on the floor ... to act as a heat battery of sorts.

The heater is set below ground level such that when I replace the soil, the cement slab and 3 layers of brick shall be beneath grade. This will help "insulate" the base of the jay, as well as act as a heat battery.

I had to cut very few brick with this design and hope to post a CAD rendering of the heater on PicasaWeb.google.Com/LARSmith217

If you have questions, feel free to post here or to my EMail address ( [e-mail] )

[rocket_richard]

Great work!! Congratulations on realizing your project. Is the inside of it firebrick, or the same brick as the outside? Can't wait to see some sectional cad drawings.

[Donkey]

Looks good. Interesting how you've opted to do away with the barrel, ETC.
I do see one thing right off though. Since your feed is so small, it looks like you may have a difficult time cleaning the ash out of it. You will need to get some kind of implement way to the back of the burn tunnel, right up to the heat riser to scoop out the ash.
Unless of course, you've got an ash clean-out somewhere hidden from sight..

[larsmith]

The whole heater is all 4.5X2.5X9 brick. I'm considering coating it with red brick, with a 1" air gap between the outer red brick and the inner fire brick. Something to create a natural heat draft into my room(s). That project may have to wait till this spring, till the weather is more condusive to brick mortar curing properly ... not too fast, not too slow 7 no freezing.

This coming week, I'll try and remember to do up a final CAD drawing and post the photos, with layers / sides removed so that the inner workings of the heater are clearly visible.

It was easy enough to build. Very proportionate. Only had to cut a few bricks around the exhaust area.

Boringly simple but based on the rocket-heater principles with regard the the proportions of the burning tunnel & heat riser.

I'm thankful for the multiple resources I found here as well as on YouTube and multiple other sights.

[larsmith]

Donkey, re: the ash clean out ... the distance to the back of the heat riser, at the base of the heater, is approx 9" and reachable with a small mason trowel. Fits in the edges nicely. Very accessible ... and as you might guess, there's not much ash left over. Because I'm using only a couple 90 degree elbows in 8" pipe, there's not much ash building up in the system, thus far.

What exit exhaust temp should I be shooting for in my chimney ?

[Donkey]

Eventually, you will need to clean it out.. All that matters is, you got a way to deal..

As low as possible while not causing a condensation problem.. Experiment. Your floor is sand, Yes? Seems like you could very quickly try a whole list of experiments down there. Shame that piping elbows are so expensive.

[larsmith]

Help me quantify "condensation problems" ... or explain ( or point to where I can read about ) condensation problems.

I'm thinking that any / all condensation can leak out from between the joints at the bottom of the pipe.

My pipe exits under my wall to the "base" of a 'T' ... one of the "branches" of the 'T' points "due down", as Winney the Poo would say, while the other branch goes "due up" and connects to my upward bound chimney. The lower "branch" of the 'T' rests on "pea gravel" that's between 6 and 9" deep and probably a foot and a half wide. I figure that any condensation which might attempt to run down the pope will eventually run down into the gravel and below that into the sand / soil below.

Presently I've only got one elbow length plus 2' plus one elbow plus one "T" plus one 2' length buried in cop / soil. I'm considering tearing up the cob / pipe and lengthening the whole process by about 14 feet ... but before doing so, I'd like to know what exit temps I should probably not drop BELOW and what range of temps I should seek to achieve.

Is there any such data available ?

[Donkey]

You have drainage, no problem.. Though over time the scent saturating your sand (assuming a lot of condensation) could get unpleasant.

The sand in your floor can hold a heck of a lot of heat.. If you lengthen the pipe runs in the floor you could capture more of it. To pin it all down better, I'd have to say do the experiments..
Run the pipe in floor out longer somehow.. Do a full orbit of the stove, or say, run the pipes down and back a couple times. Cover it over with sand and see what happens.
Repeat, lengthening the runs until you can see steam (not smoke) coming from out of the chimney.
If you get an unreasonable amount of condensation or if the fire backs up and smokes into the room then shorten the works till all is well again.

[larsmith]

re: Steam and smoke ... we're almost there as-is. I'm considering putting in another 4' of cob-covered pipe in my floor to see how much of an improvement that offers. I've got enough room for 12 feet of extra floor space, six feet each direction, to add underground / under sand exhaust pipe. I'll do it in increments.

Wish there was a way to express our gratefulness to all members here for their comments, contributions and experiments. The sacrifices y'all have made have led me to a successful implementation of my own rocket heater !!

[larsmith]

Am I correct that the taller the heat riser, the more draft and the better the heater will draw / run ?

Side question : At what sustained temp will wood spontaneously combust ?

[Donkey]

Yes, the taller the riser, the more the draft.. Up to a point.
I do believe it's somewhere between 400 and 600 deg. F.
I've forgotten. A quick google search should answer that.. Wikipedia has some great combustion entries.

As to cob covered pipe.. Sand is actually better thermal mass. I use cob to be sure the joints are solid, also sometimes I build joints out of cob and funny shaped channels where appropriate, which is cheap. Sand directly in contact with the pipes is best (IMHO)

[peterberg]

Dec 22, 2008 10:47:47 GMT -8 larsmith said:

What exit exhaust temp should I be shooting for in my chimney ?

The lowest chimney temps I get, sustainable for 10 minutes or less, is 100 F. When the first run from cold is at its peak the temp will reach 150 F. Measured in the center of the gas stream.
Having a burn staying at 100 F or below, you are probably stretching things too far.

[larsmith]

My "estimated" exhaust temps are running somewhere around 200 - 250. In the video I did, you can see a BLACK CAP which closes the base of a 'T' which I've got buried in the cob ( and acts both as a place whereby I can initiate draft in the pipe as well as acting as a cleanout )

WHen I place my magnetic thermometer on that cap, the hottest its ever run is just under 250 ... and that's the only indication I've got of potential exhaust gas temps.

That 250, BTW, is the max temp I've ever noted at the TOP of my rocket heater. ( placed the magnetic thermometer at the top center of the "arch" which transitions from heat riser to the exhaust down-draft )

FYI ... I have been using a circular saw to cut the 4-6" pieces of wood which I slide up into the burn tunnel. I've found a symbiosis between the embers in the base of the feed and the longer pieces of wood I place there-in and the amount of flame from the wood in the burn tube / tunnel. When I keep each healthy, the heater runs at it's max ( guantified only by the amount of "roar" of the fire.

I'm attending to the heater every 20 to 30 minutes and as expected, the longer I run it, the hotter it gets and the more "roar" I get when the fire is running at its best.

[canyon]

Wow! I am impressed and psyched to see and hear your rocket on the tube! Thanks so much for sharing! Looks like fun.
I guess I'm late to the conversation here but Donkey had the only comments I would've had, like about a clean out. Somehow it appears to lack one. Also, the condensation further down the line needs drainage as mentioned but also I'd add to remember that it is very acidic and will corrode any steel it forms and runs on. Peterberg made a key point that could use emphasis that the gas stream temp in the middle can be much different (higher) than the outer surface due to laminar flow just like a creek or river flows much faster in the middle than at the banks. So, we really should be talking about exit temps as measured by the middle of the gas flow (get a probe thermometer that you can stick in there) as Peterberg has been doing.
Keep up the good work!

[larsmith]

When first I embarked on this journey to build the heater, I had a dream ( not of the scale of Martin Luther King ... but a kewl dream none-the-less ). I clung to that dream, fueled by the confidence which y'all here on RSHeaters had imparted to me via your comments & threads. I ran on that fuel thru the completion of the project and voila.

Somehow in my head, I knew this heater would work, not because of who designed / built it but because of all the work y'all had done before me ... and I knew I was using many ( and obviously not all ) of the tried & true principles associated with the heater.

I felt as tho when I'd finished building it, the excitement & anticipation would be followed by a void ... and am pleased to report that's not the case. My wife and I continue to learn from the heater ... we're learning how best to get it running ( so far, this has proven to be a relatively easy heater to start up in the a.m. )

I'm learning what size wood works best and how often to feed it, etc.

I've "bermed" the heater with sand / wet clay so that the first four layers of the heater are all covered up in sand ... and then up another two layers is also bermed up with sand.

I'm learning to hear how healthy it's running, based on the amount of "rawr" going on inside.

The excitement has just begun.