Help with RMH not drafting

Hello and Thanks to all who have given me some thoughts on the problem. Your kindness is much appreciated! First to answer a few of your questions...

Yes it's in the basement, this is the only space that I have for a fireplace in my home. The exhaust exits through a 6" hole cut through a foundation block. It then goes into a short insulated piece of pipe (30") and out a short chimney ( 36") with a rotating cowl on it to reduce the down draft.

The brick column at left of my RMH was a chimney installed in 1900 when my venerable old house was built. Most of it was removed prior to me. It only goes up to the top of the basement and dead ends. I placed the RMH next to it so that it could act as additional thermal mass. Also, this location is in the center of the room.

I've tried burning with a window open. Doesn't help much.

The chimney inside the barrel has a diameter of 8 inches. The ducts are all 6 inch. (Possible problem?)

Also, the size of the manifold opening, made from a duct boot, may be too small to accomodate the 8" internal chimney. I tried to fix this by chipping it back to increase it's size convinced that this was the culprit. Nada! Nyet! Nothing!

It's an L tube right now because the J tube I constructed didn't work. It only seems to draft if I push the fire directly under the chimney and constantly babysit it. Then only a little bit. If I can get it to draft properly or, dare I dream, actually Rocket, I'll reinstall the J tube so that I can auto feed the fire.

There is no mass portion to the bench because the system works so poorly. Seems ridiculous to fill it up until the system is working properly since I may need to modify the ducts. I've covered the pipes with fiberglass insulation to keep them warm while testing and it does help, but not a lot. Also, I don't have access to clay with which to make standard cob. I live in a city and there isn't any clay in the yard, or for sale at the local dirt suppliers, Home Depot, Lowes, etc. I've checked in a 60 mile radius from home with local excavators, masonry supply stores, etc. but it's just not available. So I'm going to be using a product from the local dirt sifter place that clumps together well when mixed with a little portland cement and water. I have a few yards of it standing by for when the drafting problem fixed.

I removed the portion of the duct that extends into the second bench section shortly after the picture was taken last fall. That DID help the draft somewhat but definitely didn't solve the problem.

Another thing I've noticed is that the distance from the bottom of the barrel to the bottom of the manifold is 17 inches. In other words, the exhaust has to be forced down 17 inches before it can naturally rise through the ducts. Am I making the system try too hard?

I'll take some pictures now and get all the dimensions and be back soon. Thanks Again for talking me off the cliff....

I merged your stuff with the following thread. I hope that is okay by you.

HELP HELP HELP!!! Why doesn't my rocket mass heater draw?? Is there anyone out there that can help me figure out what I've done wrong in constructing my RMH? I have many pics of the build and really need a discusson on the phone to see if I can straighten this thing out before I consider my 800 dollar inverstment a total loss and take a sledge hammer to it and forget the whole thing. I absolutely cant burn it without massive backdrafts and filling the house with smoke. To be frank, at this point it's a fire hazard. PLEASE SOMEONE REPLY! It's February here in Michigan and I need to my RMH to partially heat my house.

Hi Michael:  Welcome to Permies.  EDIT) When you respond please start a new post rather than entering on page 5 of Erics post.  You will get a much better response that way.


Well from your pictures I see you built an L tube not a J tube. What dimension's did you use ?  Your riser looks short (but may not be)  your clay liners as a riser are probably going to crack from the sudden heat (if they haven't already)

I notice your mass pipe going thru the wall and not into that nice warm brick chimney standing there?  Do you have that exhaust stuck thru the wall directly out side ??? If so that will be a huge part of your smoke back issues.
Also without mass to heat up a rmh does not perform the same. condensation can stall your flow which of course causes smoke back.
Do you have a copy of the RMH builders guide ?  I can't recommend it enough!

Michael Solosky wrote:HELP HELP HELP!!! .

Hi Michael,
Welcome-you have found the right place for help!!  I am the least experienced here, but many others are invaluable resources.
As a new builder, I feel your frustration. Keep the sledge hammer at bay and take a deep breath.  Though now in the PNW, I hail from Ohio, and can sympathize with the weather.   I know the UP can be especially brutal.
I can offer some basic, rudimentary advice, and some of the others (I am sure) will chime in beyond that.
Here you go:

1) Go ahead and start your own Feed. (There is a way to select "New topic"- if you can't find it, someone can help.)

2)  As Thomas suggested, do  you have the Builder's Guidebook??  If not, get one ASAP.  I got one used off of Amazon for less than $30.

3) Review your critical dimensions (and POST those):  Length of feed tube, feed opening, diameter of pipes, length of total pipe run, height of burn tower (ceramic pipes), distance between barrel top and tower, etc.  Keeping these at precise measurements are KEY.

4) Post some additional pictures.  Including outside chimney set up.

Pictures, questions, pictures, questions... keep at it and we'll get it purring and roaring soon!

Staci

I moved your post to its own thread so we can concentrate on your questions.

There are a number of good questions about your build already. I can make a couple of observations.
It looks like your RMH is in a basement. This can reduce the draft because the height of the house is acting as a competing chimney. Does it make any difference when doors are closed to the rest of the house? How about opening a window in the same room?
Where is the chimney located, inside or outside? An exterior chimney will be colder and harder to get draft in.

I see you have an L-tube core; a J-tube is the usual style for RMHs and gives better combustion. Your ceramic tile riser has high mass and little insulation, so would be harder to bring up to good operating temperature, as well as being shorter than recommended for the system size. The short riser and barrel will reduce the amount of internal push you get.
The manifold transition from barrel to duct may be too small and sharp for good flow; can you post details of that area?
The bare duct you now have will shed heat rapidly. How warm is the duct surface at various points, especially near the chimney?

I'm going to second the basement thought--the house is going to be competing with the draft. And am going to third the request for more dimension info.

Something that hadn't been mentioned was the length of pipe run you have--the initial riser is pretty short--but what concerns me is the amount of pipe you have. Hard to tell, but it looked close to 50 feet which is long for a j style to push. Remember that elbows count for 5 feet each and you have 5 of them in this layout. You are definitely pushing the limit and would probably be much safer reducing this down to 3 turns and have your bench just against the one wall. Could you give us the total run of pipe as well as the dimensions of the build?

Thanks for your kind words, and thoughts. i'll be posting more pics in a few minutes. In the mean time I'll start my own thread.

Michael Solosky wrote:Thanks for your kind words, and thoughts. i'll be posting more pics in a few minutes. In the mean time I'll start my own thread.

Nope, no need to start another thread.  It's been already done by staff.



This is plainly wrong.  The  plenum you have made is way  too small.


https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

Satamax Antone, I'm sure your right! I'm going to knock out the exhaust manifold and expand it which can't fail to increase the draw. Next big question....The distance from the seal of the barrel to the bottom of the exhaust manifold is 17 inches. In other words, the exhaust is forced down 17 inches before it can naturally rise up the sloped duct work. Is that too far?

This is something I had to deal with a lot. I have an external chimney and had no choice but to deal with it. Here's the bottom line, if your chimney is cold it will not draw. In fact it may push back. I dealt with this in two ways. One is to make sure that the chimney is well insulated. If the chimney is single layer then the heat will dissipate through the sides and as it does the air will not want to rise. The chimney wants to be warm to rise and the warmer, the better. So even if you have good fire starting and the system is drawing, the heat going through the system will be dissipating rapidly, and not warming the chimney, until the whole system is up to running temps. The second is to have a way to force the draft. I use the venturi method. In the garage heater I drilled a 1/4" hole in the side of the exhaust pipe. I have an air compressor so air pressure is available. I shoot a stream of compressed air upwards through this little hole, and through the siphon effect, draws air through the system and up the chimney weather it likes it or not. This allows the fire and heat to flow through the system quicker so the hot air doesn't have time to be cooled by the mass and warms the chimney. This may have to happen two or three times until the chimney is warm enough to stay warm and flow. In the house heater I built an air pipe that enters the chimney clean-out and then goes up the chimney to just below the heater entry point. The clean-out opening was then filled with fiberglass to stop all air infiltration. I use an air mattress pump to blow a stream of air up the chimney. This does the exact same thing as the garage system, drawing air through the system and warming the chimney. In the picture you can see the pipe along the wall that enters the clean-out.
Hope this helps, Brad

Brad Weber, thanks for the idea! It may be just the thing to get it flowing in the right direction after I make a few modifications. I have a 6" duct fan that I think I'll Mcguyver into the system and give it a try. Cheers!

Michael Solosky wrote:Satamax Antone, I'm sure your right! I'm going to knock out the exhaust manifold and expand it which can't fail to increase the draw. Next big question....The distance from the seal of the barrel to the bottom of the exhaust manifold is 17 inches. In other words, the exhaust is forced down 17 inches before it can naturally rise up the sloped duct work. Is that too far?

Hi Michael,

I see that you have two issues, each to be dealt with in turn:
 1) optimizing the burn system (indoors)
 2) optimizing the chimney/outside exhaust
Breaking it down and separating them, may make it easier (less daunting) to manage.

For the first part I can offer the following suggestions:

  A)  Increase the height of the tower. Though I only am well-versed in the J-tube style, as far as proper dimensions are concerned,  the adage is : twice as tall as the length of the burn tunnel and at least 3x the height of the fuel feed.

  B) Perhaps Further INSULATE the tower.  Rockwool insulation blanket is what I am familiar with and what I used around my tower.

  C) As you plan to do...OPEN UP and ENLARGE your "area under the barrel" (manifold)- to my understanding, "too big" is not possible.  In the current system, it t looks as if there is a small rectangle space that the air is supposed to flow through.  I would imagine that this does not allow for optimum heat exchange.

  D) Review the CSA (cross sectional area) of your system.  The size of your ducting (I believe) sets that, whether you are going with an 8" or 6" system.  The opening of heat exchange from under the manifold to the outflow ducting should be at this CSA.


For chimney help, I am sure some of the others can advise.

Staci

Michael Solosky wrote:Brad Weber, thanks for the idea! It may be just the thing to get it flowing in the right direction after I make a few modifications. I have a 6" duct fan that I think I'll Mcguyver into the system and give it a try. Cheers!

What ever you do has to fit certain parameters. It has to help with the draft. It can not, in any way, interfere with the flow of air when not used. It has to be comfortable with high heat. A motor and fan in-line just won't do it.
Brad

Good Morning! I've increased the size of the manifold discharge by removing the original piece of ductwork and chipping out / grinding to make it bigger. I think it's now larger than the feed tube. Thank you Antone and Staci! Also, I raised the barrel to make a 2-1/4" height above the chimney riser. I think it was too low before and choking out the fire. Brad, if you look at the cleanout above and behind the barrel you can see a cap with a handle.  I'm thinking of installing a draft fan in the tee that will blow directly out the chimney. Cold air in the ductwork would be entrained in the flow creating an artificial draw but wouldn't be directly in line with flow path. After the system is warmed up it would be turned off and capped. Gonna think this one through some more after I see how yesterdays mods work out. Staci, thanks for your well laid out thoughts and ideas. I'm working my way down your list. I can't tell you how good it is to have you and all the permies as a resource to help me think all this through. I re-mortared the barrel on last night and won't get a chance to burn it until tomorrow morning. Fingers crossed!

Michael Solosky wrote:. Fingers crossed!

 Crossing fingers!! Folks here got me through (and still helping!) with my build.  Glad to pay it forward!
Keep us posted.

Michael Solosky wrote:I raised the barrel to make a 2-1/4" height above the chimney riser. I think it was too low before and choking out the fire.  

This is not enough in my opinion. Others might disagree.

But 8 x PI x 2.25 = 56,54 sqin.

8² x PI /4 =50,26 sqin. Not enough "clearance" between the two numbers.

Top gap should be at least 1.5 CSA.

http://donkey32.proboards.com/thread/1406/calculating-ring-circumference-projection-gap

Michael Solosky wrote: The exhaust exits through a 6" hole cut through a foundation block. It then goes into a short insulated piece of pipe (30") and out a short chimney ( 36") with a rotating cowl on it to reduce the down draft.

Wrong! You need a proper chimney.

Michael Solosky wrote: The chimney inside the barrel has a diameter of 8 inches. The ducts are all 6 inch.

And wrong again, sorry!  This you could may be get by, with a proper insulated chimney.

The "chimney inside the barrel" is called the heat riser, so we are all using the same terms. What Max is saying is that the whole system, feed tube, burn tunnel, heat riser, (ducting if any), and chimney work best if they are the same cross sectional size. Some transition areas may need to be larger to avoid restriction. A good warm internal chimney may be able to handle a slightly larger system (I have a temporary 6" insulated stovepipe on my 7 1/2" J-tube with bell).

Update: Yesterday I burned the reconfigured RMH. The changes I made were to increase the size of the exit to the manifold to approximately the same size as the feed tube, lifted the barrel to approximately 2-1/4" above the heat riser discharge and slightly increased the slope in the ducting. Results...It rocketed!!! Not exactly an Atlas 5 to the moon rocket but more like a large fourth of july bottle rocket but it DID rocket! I was able to burn it for a good 4 hours and other than the initial warm up of the system it didn't back draft. Now mind you it was quite a calm day and I did start it up with a small duct fan at first but when it was up to temp the furnace didn't kick on at all. Amazing!

To further increase the rocketiness ( is that a word??) I'm going to replace the Heat riser with a 6 " one that is the height of a full size barrel, recalculate the height of the barrel above the heat riser discharge and reduce the length of the ducting in the bench. I also plan to build and improve the exterior chimney. Of course this will have to wait until springtime as I plan to build a conventional chimney that will extend above the roofline to and the ground here is definitely frozen.

Questions: Has anyone experienced the top of the barrel concaving down towards the heat riser? I think I need a new barrel...

Also, Where can I find plans for an exterior chimney that will work well with a rocket stove?

A big shout out to both Glen and Satamax for your input. Awesome brothers!

Hey Michael;  Your barrel is fine. They all move around.    However if your barrel does not have a removable lid, then I would recommend replacing it.
When you reset it, allow for the lid flexing.

Being able to quickly pop the top and check on your riser or ash is invaluable, if you start having problems.


If you are replacing your riser.  Investigate building a five minute riser. They are the very cutting edge of RMH technology.

Hooray for the improvements and success!!
I had the same question on the top of my barrel (except bowing out instead of in).
I second Thomas' suggestion of the removable lid, as I have already opened mine up several times already, and was SO thankful for the ease and ability to do so.
I had a barrel I found roadside free. We angle-grinded the top off.  I was able to find a locking rim at an architectural salvage for $10.
Also for the riser...I THINK Thomas is referring to one made of ceramic fiberboard.  I learned of it after I had already built mine, but would have gone with that had I known.  I believe there are plans for one on some "Donkey board".
Something to consider.

Hey Mike;   Here is a link to read all about 5 minute risers.     https://permies.com/t/95849/Working-Morgan-Superwool-ceramic-blanket.

Some cost involved but you won't build a better one.

thomas rubino wrote:Hey Mike;   Here is a link to read all about 5 minute risers.     https://permies.com/t/95849/Working-Morgan-Superwool-ceramic-blanket

I missed this completely...I will have to read through and file away in my "future improvements" file.