Rocket mass heater, the flue buried in the cob mass, level or upward angle?

I came across someone's video on youtube for a heater he built. He used fire brick to build a J tube and heat riser. He then covered the heat riser, no insulation around it, with a barrel, 2 inch between top of drum and heat riser with a flue coming out of the bottom of the barrel. Pretty standard but his exhaust flue coming out of the bottom of the barrel had an elbow on it that pointed up and his chimney flue went straight up to the roof and out. In his case he did not use mass to store the heat instead used the heat given off from the barrel only. He said that the gases leaving the barrel needed to travel through a flue that was layed in an upward angle and not level. He referred to the mass heater flues of 10 to 20 feed buried in cob mass for heat storage that he has seen on utube.

Question is this: Does the long flue buried in cob need to be at an upward incline or can it be level? Not yet having built a one I thought I would ask for thoughts and input.

Thanks, Dan...

Here is his video on youtube: https://www.youtube.com/watch?v=pHS6vzVQr90

youtube is full of bullshit

Daniel Reed : Lets be kind and call an uninsulated Heat riser 1950s technology ! There are a scad of unfortunate little deviations in his build that I wouldn't

want to repeat ! In this case going straight up from the bottom of the barrel with his final vertical chimney assured him of a good draft ! A heat riser without

insulation takes a long time to start to burn efficiently, giving him the benefit of the doubt at the point that everything is ''up to operating temperature'' and

he has an efficient burn he is only getting ~ 40% ~ of the heat made radiating off of the barrel, 60% of the wood fuel turned into heat energy is going up the

chimney at high temperature and requires an insulated chimney to be safe!


This probably doubled the entire cost of the insulation and with zero heat storage his ''almost a Rocket'' is no more efficient than a regular Box type Wood stove!


Here is my quick rundown on selecting U-Tube videos. U-Tube Videos should be rated like a poker hand. A full house is a good hand -3 of a kind and a pair kicker !

The three of a kind is The videos with a 1)build, 2)use, and a 3)follow up video sequence -all about the project you are interested in .

Are things clear does the poster keep up on his comments answer questions and have useful communication with visitors ? This is a minimum standard !!!

Generally a single "Look what I did'' with no follow up is a kiss-of-death!

And a couple or more videos on another subject shows the poster is proud of the work he does and is pretty handy

In all cases ''Cavat Emptore" For the good of the Crafts ! Big AL

Please answer the posters question instead of denigrating the source of his interest.
The best answer I can give based on following the topic is based on the rebuild of the RMH in Paul Wheaton's house. It has a waist high pebble bench and the flue makes a gradual rise to the end of the L shaped bench from the bottom at the barrel exit to the the top of the bench at the flue to the roof. He rates it as not the absolute most efficient but the most goof proof for inexperienced users.

I am always building things in my head. One of my imaginary builds was to have a wall of cob or rammed earth in the center of the house but toward one end minus the door to the bedroom with the bedroom and bath on one side and the living room on the other with the RMH on the end of the wall on the open end where the kitchen/dining would be. The flue would zig zag all the way up through the wall and never be exposed to the inside before it exited the roof.

Getting back to the answer as I read it The flue can be level in the bench but starting the flow through the bench may be more difficult. If when the feed to the RMH is opened, air always wants to flow up the flue and not down it will work But that often depends more on the air flow through the house than the configuration of the flue.

Does the long flue buried in cob need to be at an upward incline or can it be level?

it can be upward or level or downward.

It is always my goal to help our New Fellow Membership find its Rocketeering footing; allowing it to grow on its own with only minimal contributions

from the rest of us with just a little more experience!

My Methods lean towards ''yes you can'' boosterism, and helping them make their own minds up that they really, really, need to build a conventional

Vertically fed J-Bend style Rocket Mass Heater RMH, ( 6'' or 8'' ) and live with it before attempting to improve on a classic ! Others may have different

opinions! If I fell short of my personal goal I am sorry and apologize !


- ever had that experience of arriving latest a movie showing and find out as the film progresses that you have been rooting for the Bad Guy !

And then there is the ''can't see the forest for the trees !'' Event



I am making a link here to review a little ancient history }}}-----> see link below :


https://permies.com/t/21034/rocket-stoves/free-advice


This is not really about any Begrudging of free advice -as it is about reacting to being asked to make a Silk Purse out of a Sows Ear ! If any are

brand new to Rocketeering we freely expect that our members will be impeded in their 1st efforts to Learn the Ropes and confidently grow well

informed when there is so much crap out there ! As this is a continuous multi-year ongoing problem the repetition tends to wear some of us Down !

Again if I am slightly peevish- It is still very important that my comments are well directed ! So - 3 times Sorry, Sorry, Sorry !

For the good of the Craft ! Big AL

As far as the question about level or angled flues, I would expect that a level flue (what would go through the mass) is probably going to work, but having a slight rise (an inch or two every 5 feet or so) can help. Not only would it help with drafting, but also with moisture. Especially when the mass is drying out, you'll find a lot of moisture needing to go somewhere. Directing it intentionally is better than not.

In the case of my RMH, an accident appears to have helped. My mass is made from poured concrete. We laid the flue pipe with a slight rise and made sure it wouldn't sink lower as we poured the concrete. Unfortunately, we didn't expect that the pipe might try to float. A mad scramble ensued as we saw the problem happen, and we ended up with a flue that rises from the barrel, reaches a peak (serendipitously right where I keep my shower towel!), and then slopes downwards as it exits the building. What happens now is that some of the water comes back down, but some drains out, and there is a warmer spot on the mass bench. Last winter it created a nice stalagmite as the water drained outside.

I'm hoping this winter there won't be as much moisture created as the mass is much drier and so is the wood I'll be burning.

I want to thank you all for the input. As of this writing Dec. 16, 2015 I'm still in the planning and education stages. I built a 16x28 barn/workshop (the first structure after clearing build site in wooded land) and a travel trailer as a 3 season residence. Actually it was the second building I put up. The first was the out house. I have my prioritys. I plan to insulate and make the barn a 4 season structure this summer and building a RSH in it. Then I will build the cabin and plan to expand and capitalize on my experience by building another RSH.


Also, anyone have any luck with mixing cob in a 4.1 cubic foot 1/2 hp electric cement mixer, is it practical and doable?

Thanks again, Dan...

Daniel Reed : This is a follow up to my warning about crap on U-tube , this is some of the good stuff ! ///// See link below :


https://www.youtube.com/watch?v=30rPCRB5e-s&list=PL0bZy202ImXP7NpLUJMtKJOjpjPPv59b-

This is Rocket Stove porn ! For the Good of the Crafts ! Big AL

And this is another Ernie and erika build just going into a 3rd winter now ! ///// Link Below :

https://www.youtube.com/watch?v=W3TwEhjTwb4

a.l.