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What did I do wrong? Won't Draft???  RSS feed

 
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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?
 
pollinator
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Can you remove the shorter feed riser and see how it works then? If your exhaust riser has a much greater cross-sectional area than your burn chamber, then the gases will slow down in the riser and make drafting more difficult. Here is a plan to test and see what the problem is:

1) Start with just the horizontal burn chamber. If you put some kindling into it and light it on fire, it's not going to draw very well at all. You probably will have to blow on it to even get it to draw at all. But after a little air flow gets started, it should draw air in one end and exhaust the smoke out the other.

2) Now stick the exhaust riser in place and see how this improves things. Gases that enter the riser will be expanding and less dense, so as they go out the top, air will begin to flow into the burn chamber and you will be getting a self-sustaining draft going. Putting a chimney on an enclosed fire really has a way of establishing a flow of air!

3) Once the draft flow has been established, then add the short feed riser and see if it still drafts. Unless you have have some big blockage, this is not going to appreciably cut down the air flow.

Another way to get a sense of how rocket stoves draw is to make one out of stacked bricks.



If you go through this exercise, you can see how the fire starts with no particular draft, and then as air comes in one end cold and goes out the other end hot, it turns into a rocket stove with its characteristic rocket sound. Keep experimenting, you'll get there!

 
pollinator
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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books fungi hugelkultur solar wofati woodworking
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John with a Constant Cross Sectional Area In your Feed Tube, Burn Tunnel, And Heat Riser, the Total depth of the Heat Riser to the bottom of the Burn Tube Should be 3Xs the
Depth of the Feed Tube !

Have you been to rocketstoves.com to get your PDF Copy $15.oo of Ianto Evans' book "rocket mass heaters", There is STILL no other Book in any Language with More
rocket mass heater Family information, in any Language ! ( and I still dont make a dime ! ) Hope this helps !

think like fire, flow like a Gas, Don't be the Marshmallow ! As always, your comments and questions are solicited and Welcome ! PYRO - Logically BIG AL !
 
Ted Visner
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I had three fire bricks creating the ceiling of the horizontal burn chamber and I took one out and it drafted for a full 2 hour burn
but it still never made the rocket noise. =(
 
Ted Visner
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This is a great website with a lot of really great information!

Hopefully today I will be able to shoot some video of my MRH in operation
and get it uploaded to YouTube.

When I shortened my horizontal, the performance improved greatly but the reduced draft still allowed the fire in the feed tube to climb
the wood in the feed tube.

Does the riser in the center of the 55gal drum need to be in the center? If I move the the drum a little off center, I could remove another half brick
from the horizontal burn chamber.

Another thing... I still have all of my ducting exposed and the joints could be leaking (sucking) air?
One more thing... With all my ducting exposed, water has leaked out of several of the joints.
Is this from the wet mud or is it condensation to be expected? The amount of water was about 2 cups.

THANKS!

Ted
 
John Elliott
pollinator
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Good to see you are making progress! I would go ahead and remove the half brick and let it be off-center. Performance is more important than aesthetics. As to whether is it sucking air, you can always test with a tissue. If you lay a tissue on the joint and it firmly stays there and you have to peel it off, then that's an air leak.
 
allen lumley
pollinator
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Ted Visnor : Yes, You Definitely can off-set your barrel to 1 side ! You will be creating a hotter and a cooler side by doing this, some times it makes it possible to tuck your
rocket mass heater R.M.H., into a corner with flammable exposures! The side with the wider gap should be the side where your hot exhaust gases leave the bottom of the
Barrel to flow horizontally over your ash pit and past a clean out, You have a barrel with a removable top and that reduces the need for a clean out and an ash pit, Every
R.M.H. has it's own characteristics, only time will tell how well this works for you, Donkey is experimenting with a Heat R that has a pronounced flair like the mouth on a
Trumpet to see if he can get settlement of fly ash out of the Heat Riser Column, getting the ash to settle within the Burn Tunnel, this may work very effectively at the end of
a burn cycle using a 'lick and a promise' type vacuuming before the next fire !

Can you tell us where you scored your barrel and what it held before you got it !?!!

I have never used backer board so that I can not speak to its strength and weaknesses, but the Cement in your cinder blocks Will start Failing when exposed to Temperatures
at 400 F . Also radiant heat will cause out gassing of your insulation the way you appear to be using it (in the pictures ) Underneath your R.M.H., you need an air break and a
radiant heat barrier, even if it is only aluminum foil glued directly to the Floor .

It seems a little late to ask, but have you been to rocketstoves.com for your PDF Copy $15.oo of Ianto Evans Book 'Rocket Mass Heaters there is STILL No other book in any
language with as much rocket mass heater Family information (and I don't make a Dime ! )

If you want to see more about a safe build over wood,and other Combustable materials, you can look at page 62 in 'the Book' or you can go to the rocket stove Forum/Threads
and click on ''Is Erica and Ernie's DVD for sale anywhere?", then click on and scroll down to to the 1st picture, click on the picture to bring up a larger image, then by using your
mouse to enlarge the picture as you scroll over it look at the space where the wooden floor meets the Thermal Mass Bench and notice the air channels that circulate Air under
the Bench, and up the outside wall, you can see the air vents at the top off the window/seat back area !

Finally, you can check out ernieanderica.info for more information on their 'Bonny Convection Bench'- I hope this helps and is timely ! For the Good of the Craft !

Think like fire, flow like a Gas, Don't be the Marshmallow ! As always, all your comments and questions are solicited and are Welcome. PYRO - Logically BIG AL !
 
                    
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Location: AR ~ozark mountain range~zone7a
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hey Ted, I could be wrong about this but it might be worth your time to double check your measurements, your metal duct pipe looks small, as compared with your red heat riser. The idea on a RMH is to keep the various square/round/rectangular AREA of the passages all fairly consistent in size throughout the system. If your red heat riser is 6" square on the inside, the AREA for that cross section would be 36" sq. inches. If the metal duct pipe is 6" round on the inside, the AREA would be around 27".

I don't know what the inside of your burn tunnel AREA is but it should match the other passages, regardless of shape. Except at the connection point of the metal duct pipe to the stove, that opening or collection point is often improved if the pipe connects to the stove with a larger AREA transition, or manifold that gathers or 'funnels' the flow into the metal duct pipe.

Don't worry if your stove doesn't make a lot of noise, a loud stove is the scariest of all!

james beam
 
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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
 
Gerald Gobb
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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.
 
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I would say your heat riser is too short. On mine I used 2 pieces of clay tile for the riser. Well I should say I will before the week is out.
 
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