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Rocket heater not drawing. HELP!!!!!!  RSS feed

 
tim eden
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Hello energy savers
We just finish welding together our new rocket heater we made out of an old water heater. It has a 6" barrel made from to old fire extinguisher wielded together the riser is insulated with vermiculite and capped in clay. The top of the riser to the top of the barrel is 2" could this be to much or to little, also the top of my barrel is round? We are having trouble getting it to draw when we put the barrel on top of the riser, without the barrel it is a rocket. I attached a few pictures of it . I also wrappped copper tubing around the heat riser and ran it out the bottom so i can heat the water in my fish tanks through a stainless steal radiator. Any suggestions on what i need to check PLEASE let me know. I am setting this up in our greenhouse. Thank you for reading and stay green! Tim[/b]
rocket-barrel.jpg
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rocket-and-pipe.jpg
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rocket-2.jpg
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paul wheaton
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My first question: do you have the book?

next: I think it is critically important that the burn tunnel is insulated.

 
tim eden
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I have the rocket mass heaters book by Ianto Evans & Leslie Jackson. By Burn tunnel do you mean the area between the feeder tube and the riser? Thank you so very much for your help Paul.. I am all ears!
 
paul wheaton
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tim eden wrote:By Burn tunnel do you mean the area between the feeder tube and the riser? Thank you so very much for your help Paul.. I am all ears!


Yes.

The feeder tube doesn't need insulation. In fact, I kinda wonder if it all might work better if it didn't have insulation. But the burn tunnel (where the sideways burn happens) needs to be insulated. The fire needs to get so hot that you get the reburn in the heat riser. And the rockety effect.


 
tim eden
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Should I use cob all around the burn chamber to insulate?
 
paul wheaton
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tim eden
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I added perlite to the cob & sand mix?
 
tim eden
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Also instead of straw to make my cob bench, can i use large pine needles they are almost 10" long? Thank you again for all your help, i have the chamber insulated now and waiting for it to dry
 
Brad Davies
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tim eden wrote:Should I use cob all around the burn chamber to insulate?


I can't comment on the insulating properties of cob as I have no experience with it yet. That being said I wouldn't imagine it to be a great thermal insulator based on its compostition.

A thermal insulator is something that slows the transfer of heat from one surface to another. Usually this is done by having captured air pockets in the material. Non moving gasses, or air in this case, are very good insulators because the molecules are sparsley spaced so they have hard time transfering energy from one molecule to another. For example if you place 3" thick pink fluffy insulation in a 3" cavity it will work with the R value listed. Now if you pack the same 3" space with as much insulation as you can fit it will work less effectively. You squish the air pockets out of it and it no longer works as an insulator.

Thermal mass is something that readily absorbs, stores, and re-emits heat. Solids and liquids work well as thermal mass because their molecules are close together. Stones, boulders, water all make excellent materials for absorbing and re-emitting thermal energy, but not for insulating.

An example that might help would be if you have ever been swimming and heard a boat go by when your ears are under water. The boat sounds way louder, and way closer when your ears are under water as opposed to in the air directly above the water. This is because the sound energy travels easier through the material that has more densly packed molecules. Heat transfers through materials in much the same way.

I don't mean to imply that you didn't know the difference between the two. It just seems to be a very common misconception.
 
tim eden
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It did help to insulate the burn chamber, but seems to still need more draw? The throat of the burn chamber is backing up with hot coals and closing it off?
Any suggestions?
in advance
 
paul wheaton
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tim eden
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1.75"
 
tim eden
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Hi Paul
Top of the riser to the top of the barrel is 1.75". My feeder tube is 6" from the top of the burn chamber to the top of the feeder tube is that to high off feeder tube (6"feed tube)? I think it maybe be heating the metal feeder tube and causeing less draw through the burn chamber? Thank you again. Tim
 
paul wheaton
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tim eden
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Here are the only pictures I have, my computer is down . The exhaust is 6"
barrel-to-exhaust.jpg
[Thumbnail for barrel-to-exhaust.jpg]
exhaust.jpg
[Thumbnail for exhaust.jpg]
 
paul wheaton
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I suspect that the bottleneck is where the bell meets the exhaust duct.

I am imagining something where there is a half inch between the bell and the heat riser. And there is six inches across the top, and an inch or so along the left edge and an inch on the right edge. So this would be about 4 square inches of space for the exhaust to move through. But a six inch system requires pi * 6 ^ 2 -> pi * 36 -> 113 square inches.

 
                            
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Paul,
Any chance you think some of the issue could be the ratio of the system heat riser vs horizontal burn tunnel and feed? In the pic they look pretty close 1:1 vs the 2+:1 recommended in the book and on this forum.
 
paul wheaton
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Hoser Hatfield wrote:Paul,
Any chance you think some of the issue could be the ratio of the system heat riser vs horizontal burn tunnel and feed? In the pic they look pretty close 1:1 vs the 2+:1 recommended in the book and on this forum.


I think you make a really good point.


 
tim eden
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My riser is 22 and the feed and the burn tunnel is 12 .
 
                            
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22":12" less than 2:1 plus you need to add in the wood feed so much closer to 1:1. I would add 6" to the riser at least, may need to double it or shorten the horizontal burn tunnel.
 
Gary Park
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I second the notion of needing a taller riser. If your total flue length was pretty short you could probably get away with such a short riser, but with that much pipe to push gases through sideways, that 22" is just not going to cut it. My opinion that is.
 
allen lumley
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- pine needles contain pitch, so no ! Great length is not an asset its helping the sand and clay to bind at the granular level to one another while lightening the final mix !

People have used last years cattail fluff and look how short that is ! Take this question to the Cob forum and tell them how you want to use It !
 
Thekla McDaniels
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Mine isn't drawing well either. It is brand new, first fired last week. Briefly: a 6 inch system with 18 feet of heat exchange tube before exiting the cob wall of the greenhouse. The barrel is a 14 inch diameter grease barrel. I don't want a lot of heat off the top of the barrel, so I left more than a 2 inch gap between the riser top and the barrel top. The riser is 28 inches tall, from the top of the burn tunnel to the top of the riser. I notice someone said something about the length (or height) of the feed tube. The top of my feed tube is 2 1/2 inches taller than the top of the burn tunnel. I've got the Evans & Jackson book, and can check the dimentia and proportia drawing, but I thought I had it right. If what I have is the absolute barest minimum, will it draw better if I add some height to the insulated riser?

What happens is the fire crawls up the sticks in the feed tube and there is not enough draw to pull the fire and smoke into the burn tunnel. I'm burning 2x4 and pallet wood, split small, and I watched all the videos on

http://www.richsoil.com/rocket-stove-mass-heater.jsp

last night, paying particular attention to the hand full of split sticks going in to the tube in the portable RMH, and
Ernie showing us his punky wood. Still, I'm wondering if the wood needs to be harder wood, and therefore slower to creep up the sticks.

It burns the right direction for a little while, then burns backwards billowing smoke into the room. It just isn't sure which way it is going. I've checked the clean out and cleaned the burn tube. I have generated enough heat to dry out the wet mortar -- but the pipe where it goes out through the wall at best has been barely warm. We had a windy day, where it seemed the flame burned better when the wind was in a particular direction. I thought that was a sign that I needed to take the stack up higher than the roof, and now that I've done that there is not much change.

I read above about the peter channel, which I had heard of on Donkey's site, but I did not understand it. I think I understand it a little better now, but 5-7% of what? the CSA of the burn tunnel, the feed tube, or the 6 inch diameter of my heat riser and heat exchange tubes.

If I need to extend the length of the heat riser, (which I am using stove pipe for, because there is not room inside the barrel for a hollow brick tower) can I just add pipe to the top, and bring the insulation up higher, or will I have to replace the 28 inches with a single piece of stove pipe?

beyond thanks!
Thekla
 
Ernie Wisner
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Taller heat riser, 1 1/3" gap, full manifold, if you did all the work on the system cold you need to warm things up a little so you get flow. a small candle pushed under the heat riser for 15 to 20 min will get the flow moving in the right direction.

several times i hear of folks lighting a new stove and it pulls for a short time then just billows smoke, often this is because of a cold air lock in a corner or something. this is why i try to build with the RMH burning. a hot build does a couple things; 1. expands the ducting so you dont get cracking. 2. keeps the system warm for the first charge to the mass.

we tell clients to start the stove slowly with the candle trick then build the rest of the fire when first lighting it for the year. The dimensions and proportions in the book are not quite what they need to be. We the researchers (this includes many of you) have dialed the stove in much closer to its best performance and this has not been reflected in the book as yet (the book is currently going through another rewrite/update). So please hang in there we learned alot of new stuff since the last revision and are working on getting it out for all to see in the same friendly language.
 
Roy Emerson
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First reaction is that the horizontal burn tube is too long. Second, not enough rise in the stack to achieve barometric differential (chimney action), and third -- have no fear -- solution is simple: just add (6"?) by 2 ft. sections of stovepipe until you get that audible "rocket effect". Also, if new stack section(s) are insulated, depending on your application, it will be safer, and enable the chimney action to take effect much more quickly. My stove is also a boiler with 2 coils --ergo, high restriction, so I use a small draft inducer fan just to get things established. Further, we must remember the simplicity of the "rocket" concept. which is the shortness of the combustion area as it relates to the 90 degree upturn of the "stack", and the turbulence caused by the turn. I complicated the basic principle by using "on-hand" materials, and by preferring to use H2O as my mass heat storage medium. Forgive me for that, since I am an HVAC pro, enamored of water as a transferral method, since water lends itself to being heated by a great variety of means. Also, storage is easier, provided one has midrange plumbing skills. The draft problems in my system are mainly caused by the efficinecy of heat transferral to the water medium, thereby resulting in much lower "stack temperatures". The addition of a draft inducer creates much the same effect as it would in a "90% plus" efficiency furnace, in that it tends to create a vapor plume and condensate in the flue. These problems are not insurmountable -- all one has to do is anticipate the "low" spots, and provide passive drainage. Also, the draft inducer can be thermostaticallly controlled, so that it is not running 100% of the time. Actually, the higher your combustion temperature in the burn tube, the less likely you will have to handle condensate accumulation. My RMH boiler runs at temperatures where the flue temperature has yet to exceed 90 degrees Fahrenheit. I do get a little vapor plume at this temp, but not enough to have a condensate problem. This could probably change, depending on the moisture content of the fuel I am burning. In fact, most of the time after the combustion is established, the effluent is CLEAR. Oh, P.S.: Remember that controlling the burn is instrumental in the absolute maximum amount of heat obtainable from your chosen fuel, ergo, the maximum efficinecy. Therefore, the lower your final exhaust temperature. the greater the amount of heat you have "reclaimed".
 
Thekla McDaniels
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Gosh THANKS guys. This gives me hope that it will be burning with enthusiasm quite soon.

Ernie, you night owl, I don't know what you mean by "full manifold". And I followed your alot link and enjoyed it "alot". Next Komondor I get maybe I will name Alot.

Anyway, Roy mentioned the length of the burn tube, and since there is an important relationship between burn tube length and riser height, I thought I might make the gap at the top of the heat riser smaller as you suggest, and shorten the burn tunnel and change from steel to brick.

The maximum I could extend the heat riser is about 4 inches. (The ceiling is not fire proof! Right now, I have stone and brick stacked with gaps to absorb and deflect the heat)
If shortening the burn tunnel sounds reasonable, I wonder what is the minimum length a burn tunnele ought to be? I will fess up here and perhaps we'll find another reason my stove is a reluctant rocket. I'm using 3/8 thick steel square tube, with not much insulation around it. The bottom of the feed tube is level with the bottom of the burn tunnel.

Roy, no electricity in the little building, but I'll admit I have thought of building a set of bellows, because I really need the air to flow in there and I get tired of blowing.

So, I'm out to do the morning chores and will remove the barrel to check things out inside. I'll photograph what I find, and check back in before I go shopping!


1 fix the right gap at the top of the burn tunnel,
2 replace the barrel,
3 light a candle at the base to warm things up while I

recheck wonderful permies.com for help and perspective

4 go get some fire brick, and make a warmer shorter burn tunnel.

Thanks to both of you! And everyone else whose experiments and adjustments have contributed to the body of knowledge.

Thekla
 
Thekla McDaniels
gardener
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Location: Grand Valley of Colorado's Western Slope
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Well, never mind. I must need a break! I thought I had found that the CSA of the burn tunnel was bigger than the CSA of the riser and all that other 6 inch pipe. Couldn't believe I had made that error, but at least it would have been an easy fix.

Rechecked, and got the original figures, in which the CSAs are matched. 5.25 square burn tunnel CSA 27.56. 6 inch diameter pipe. CSA 28.26

Always make NEW mistakes!

I'll just go fix the top of the heat riser for now. At least it is a sunny day,and lots of solar gain in the greenhouse, won't need to burn to add heat.
thanks again

T
 
Thekla McDaniels
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Thekla McDaniels wrote: I thought I had found that the CSA of the burn tunnel was bigger than the CSA of the riser and all that other 6 inch pipe. Couldn't believe I had made that error, but at least it would have been an easy fix".

Actually, what I meant to say above was that I thought I had discovered the opposite, that the burn tunnel CSA was a lot larger than the 6 inch pipe CSA. I really DID need a break!
 
Thekla McDaniels
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Update on my stove:

Yesterday, I did as advised. Removed the barrel, added a total of 4 1/2 inches to the riser and insulated it, made the gap between the barrel and the riser 1.3 inches, replaced the barrel. I fired it up. It burns into the burn tunnel. It draws better than it did, but the piney stuff still burned up out of the feed tube. Today, I burned dry fruit wood, and I did not have that problem. I still wish for a more enthusiastic draw. What I had before was an occasional fluttering sound, today it was a sustained flutter. Tomorrow, I plan to trade the metal burn tunnel for brick and add as much insulation as possible to the base of the combustion unit and burn tunnel.

I think I have a lot to learn about vertical feed and horizontal burn configuration. Slowly I am gaining some sense of how to make it work. If the season ends with my stove still not very rockety, despite being thoroughly dry and warm, then I'll search out a 55 gallon drum to switch for the smaller barrel next summer... increase the riser height, get triple the insulation on the riser, and modify/fireproof the ceiling. As it is the stove is burning just well enough to slowly dry and heat the mass that I am adding in stages. Today, with solar gain, the temperature was 90 degrees. I expect tonight's overnight low in the greenhouse will be in the high 50s. My objective is to be able to germinate pepper and tomato seedlings in there starting in 3 weeks. To do this I'd like to have the over night temp on the surface of the mass bench go no lower than 60-65 F.

Thanks for your help, and thanks for this forum!

Thekla
 
Dan O'Connor
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OK GUYS,

I could use a little help with my new stove not drawing so well. It is in my green house, I have about 30' of horizontal 8" exhaust pipe running through my planting beds, My heat riser is 8" with about 4.75" of vermiculite and clay all the way around it and it is 34" high. The drum on top has approx 2" of gap on top and on the sides. The burn tunnel is 4" x 6.75".

I can get it to draw, but it is very weak. My main question is: Can I expect it to draw/rocket better if I add about 7" to my heat riser? (if all else is OK)

I also would like to know if just straight vermiculite would be the best insulation for the heat riser in future builds? (light and airy??)

Thanks,

Dan O
 
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