Peter van den Berg

Yes, it's about Minnie Mouse. It's the only one J-tube I did at permies.

paul wheaton wrote:Peter van den berg did build one rocket mass heater here with a steel burn tunnel (not a steel riser) and was able to get it to work with two design decisions:

a 4 inch system (cannot burn much fuel at one time, so the system never gets very warm)
air is pulled into the system in such a way that it cools the steel.

Sorry, this is not entirely correct. The top half of the feed tube was made of steel with a built-in secondary air provision. Which allowed it to be cooled below spalling temperature. The hottest parts, being the lower half of the feed tube, all of the burn tunnel and lower part of the riser were all made out of refractory concrete.

During experimenting in the years before, I welded a complete steel 4" J-tube. The bottom part of the feed tube spalled heavily, so I reckon that would be the most vulnerable spot. Mark this was a small system, it might be different in larger systems.

Just another hunch: mount an elbow high inside the bench. The open end could be used to house the bypass valve. As a rotating one or sliding one, your choice. The rod should be situated horizontally in order to use the winged copper tube, I need to add.

Ruben Masson wrote:How do I seal the metal rod coming out of the bench, so there's no smoke/gas coming out of the system. I imagine some kind of rubber seal in the cob where the rod moves through, but can't find anything for that online. Also the rubber has to withstand quite some heat..

Hi Ruben,
Best solution I've seen so far is guiding the rod through a piece of closely fitting copper pipe. Just to get it through bricks and cob and whatever. In order to keep the copper pipe fixed in place, solder a strip of copper plate at right angles to the pipe. This will keep the guide pipe in place. Those wings are meant to be placed in a seam between bricks.

For your information: the whole of the system will operate in underpressure so when running smoke won't come out anywhere. While starting cold that's another matter, but that effect disappears magically once the chimney draw is established.

Hi Eric,
I now understand YouTube videos were your main source of information about batch box rocket heaters.
Maybe you didn't know before but there's a website about this type of heaters for almost 6 years now. It's translated in a multitude of languages, English being one of those. Please see https://batchrocket.eu/en

Assuming a couple of things: you built it with a grate and air provision under it? Better over the grate instead, nothing at all through the ash pan level.
The  batchrocket's proportions are quite strict, it would work much better when one is adhering to the recommended values. It amazes me it works like this anyway, it has something to do with wall area versus volume ratio which is getting more favourable in bigger versions. The port seems to be the right proportion to the riser, though. You found out yourself the top deck of the thing will get awfully hot in your construction. This design is real tight, build it as recommended and it will work as it says on the tin. In fact, it doesn't act much like a wood stove, more like a wood gasifier instead.
Good luck!

Michael Var wrote:The problem I see with rocket heaters for my purpose is that they are said to be for smaller stoves in comparison to the Kuznetsov types and I want to heat a larger farm house with only one stove. To replace the cast iron stove that is filled every few hours....

It depends on from which side you are viewing it. Biggest batchrocket mass heater to date is a 25 cm (10")  version and there's a 30 cm (12") double riser contraption in Argentina. That latter one isn't a pure mass heater, built specifically for a community builing. This isn't occupied permanently so a real mass heater would be far too slow for this purpose.
There are some limitations what a mass heater of whatever size could heat, above a consize explanation is offered. Thanks Byron!

In short: to date, the design of the batchrocket combustion unit has proven to be fully scalable. One could wonder what the upper limit would be, assuming there is any.

Back in 2008 https://donkey32.proboards.com/thread/40, I tried to mimic the so-called dry slots in one of my early rocket(ish) experiments. The slots in several sizes left and right, larger and smaller, higher and lower in a multitude of combinations or completely closed.

To the naked eye, compared to no open slots at all, there wasn't much of a difference. The Testo gas analyser could find some though, chimney temperature consequently did rise somewhat quicker with the slots open. And the carbon monoxide content in the exhaust gasses rose to alarming levels, which is a sure sign of incomplete combustion.

Without a gas analyser one could conclude combustion was more complete because of the higher exhaust temperature but in reality it wasn't, rather the opposite. The ballast gases weren't separated from the combustibles (CO being one of the latter) and some amount of the hot gasses produced went straight through the chimney into the great outdoors.

My conclusion at the time: the theory is probably flawed in the sense that the predicted effect was neither repeatable or provable.
The hallmarks of a good experiment are that it is provable, transferable and repeatable. Given the absence of two of these necessarily parameters, it's unlikely it would work according to the theory.

Just my two cents.

Ivan, it looks like you have a piece of steel stove pipe inside your insulated riser. This is doomed to fail, the steel will be corroding like mad in a high-temperature and oxygen-rich environment.

Glenn Herbert wrote:Edit: batchbox.eu definitely doesn't do anything if you type that in.
"The batchbox.eu site no longer seems to be working..."

No wonder, as far as I know of, there's no such site. Not run by me, anyway.