The need to insulate the riser is driven by what?

"Insulating the riser" does not mean making a high-mass riser that retains heat for hours; the most efficient risers have very low mass and high insulation so that the combusting gases make the whole interior hot within a few minutes. Combusting gases may be hot, but they have very little mass compared to even a lightweight riser, so they can lose significant heat and combustion efficiency even in the short trip up a cold riser.

You especially want the riser insulated in a mass heater so that the area surrounding the riser does not get heated up to near the same temperature as the interior of the riser and thus reduce the condensing/contracting draft effect going down from the riser exit.

Glenn Herbert wrote:"Insulating the riser" does not mean making a high-mass riser that retains heat for hours; the most efficient risers have very low mass and high insulation so that the combusting gases make the whole interior hot within a few minutes. Combusting gases may be hot, but they have very little mass compared to even a lightweight riser, so they can lose significant heat and combustion efficiency even in the short trip up a cold riser.

You especially want the riser insulated in a mass heater so that the area surrounding the riser does not get heated up to near the same temperature as the interior of the riser and thus reduce the condensing/contracting draft effect going down from the riser exit.

Insulating the riser is a human reaction to an issue created by overfeeding the RMH beyond its ability (design) to provide complete combustion in the riser. Complete combustion is a balance between fuel and air (feed rate) to provide the correct mixture for a clean burn or 'complete burn'.

Being impatient has driven the notion that Insulating the riser will solve that issue further evident by the need for secondary combustion air. Also system down stream design is as critical if not more important as the riser performance in providing the draw... (not push) required for the system to perform.

Riser temps once a draft (system draw) is established is mostly insignificant as the combustion mixture is travel to fast up the riser to be influenced.

A stalled RMH is operator (and possibly design) error of overfeeding the dragon aka back pressure. I understand the need for better performance but after a lifetime of troubleshooting errors failures fall equally among equpment & controls, engineers and operators.

Heat can not travel fast enough through whatever the riser is constructed of (unless its thin wall metal) to stall the system, that is an imaginary assumption.

Ernie and Erica Wisner have vast practical experience with RMHs (hundreds of systems built), and their experience is that these factors do matter. Do you have experience to refute that?

Re "overfeeding an RMH" - a properly designed J-tube system cannot be overfed; there is not enough space for more wood than the system can handle.

Glenn Herbert wrote:Ernie and Erica Wisner have vast practical experience with RMHs (hundreds of systems built), and their experience is that these factors do matter. Do you have experience to refute that?

So I have to get “PIE” to give a thumbs down – cute...

So Glenn you are deferring to the Wisner’s?

I’ve already stated my experience. As a seasoned troubleshooter that has been following RMH’s and such off and on for at least 10 years, the same issues persist with different fixes employed, some good, some not so good. Sometimes it takes someone outside the ‘feed tube’ to realize the issues affecting performance on a theory not yet perfected, you know science is never settled like climate change.

If you change the way you look at things, the things you look at change.
- Wayne Dyer -

ENDLESS Oil
https://www.forbes.com/2008/11/13/abiotic-oil-supply-energenius08-biz-cz_rl_1113abiotic.html?sh=29e78c8e3f9e

Glenn Herbert wrote:Re "overfeeding an RMH" - a properly designed J-tube system cannot be overfed; there is not enough space for more wood than the system can handle.

Overfeeding a properly designed J-tube depends on how everything after the RISER is configured.

Properly designed means that everything after the riser is configured correctly, as well as the core itself.

Hi Joe, I have said myself, numerous times on this forum that the development of rocket stoves is far from complete and I doubt that it will ever reach the true potential until a large company with enough resources to fully develop the concept with the time and money required.
However, I feel we need to offer full respect to the individuals who have already put so much effort and time into improving and adjusting what we already have,
Designs like the batch box are very well developed and seem to work very well!

I dont know if you are right or wrong and I dont know the answer but I do enjoy reading about any ideas folk might have and you have made some interesting statements!
I really did think that you would be pounced on with negative replies but, the fact that no really  negative comments have been made, perhaps suggest there is something in what you say!

My first stoves used full refractory risers insulated from the outside and they worked very well.
My later attempts used ceramic fiber inside a metal tube and they also work very well but there are considerable differences between the two.

To start with a so called 5 minute riser is very easy to build and will last for a long time where as most refractory risers are far more time consuming to build and prone to fail over time.
So from that prospective it seems to me a better option to use an insulated riser.
My stoves are used for cooking and the heat up time on the top of the barrel seems to be much quicker with a ceramic fiber riser.
I was hoping one of the more experienced designers would chime in as it is an interesting subject….

Fox, have to agree those leading the exploration and innovations of Rocket systems indeed deserve recognition and respect. There is for sure some neat stuff out there with more to come where the ‘open source’ attitude by most is most welcome. That said I do have a few ideas to enhance RMH’s operational characteristics and safety, untried at this time but are tweaks to existing proven/employed tweaks and concepts – operational enhancements (AHA moments!!!).

Configurations and materials to build Rockets and how they are installed are only limited by ones imagination and understanding... how they understand, where those doing it have put themselves out there. Will Rocket Mass Heaters ever be taken-up by corporate research is a good question. For that to happen the personality of each system has to be eliminated to standardize for operational and repeatable results where those interested in THE DRAGON will most likely shy away from a mass produced system(s), I will.

My driving design factors are waking up to a warm space to start the day in a remote off-grid location, a RMH system that puts the majority of the heat into a heat sink (earthen floor). Employing a longer firing cycle once a day in the evening, overheating of the occupied space during firing is a major factor needing to be avoided. The structure will be a 200 sq. ft. stick frame on an insulated concrete footer/stemwall, a sleeping shack for 8 complete with loft space.

I’m looking for comfort waking up to start the day in the wilderness... getting a restful night sleep or not being hesitant of going outside in the cold to take a leak. Girls will have accommodations inside for business.

This post titled “The need to insulate the riser is driven by what?” might be seen as a trick question to some as there’s several answers as well as positions, some absolute, others not. I’m not absolute either way in fact today ceramic board for the J-tube is being consider in conjunction with dense fire bricks, this will eliminate any type of brick mortar being needed for the burn tunnel and riser assembly allowing elastic movement under fire (the feed tube would be mortared).

So my use of an insulator has nothing to do with increasing riser temps as I don’t think it’s needed whatsoever especially with my tweaks.        

Fox James wrote:
I was hoping one of the more experienced designers would chime in as it is an interesting subject….

Joe Danielek wrote:

Another assertion that of the ‘push–pull’ theory doesn’t make sense that Thomas indirectly dispels himself by stating “... however you need to start and keep a steady draw thru the entire system.”, thus the bypass blastgate for sale on your site. For me the secret to system efficiently is at the feed tube by fuel size and rate of feed to assure a complete burn up the riser.      

Just read THE ROCKET MASS  HEATER BUILDER'S GUIDE by Erica & Ernie Wisner. They never mention PUSH only 'draft' and 'draw' which is interesting.