Peter van den Berg

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.

Not that odd, the Dutch version was there first and to all the others were subsequently /en or /es or whatever added.

While the site has a row of names like that, it should come up with the translation that is normal for your country. Unless... your browser isn't configured with English as the preferred language?

tom ferrier wrote:Oh yeah! Any suggestions on what to use on the forms for waterproofing and non sticking.
Used oil? .....Vegetable oil?

I used wax for 20 years until I discovered WD40 oil. Add sparingly and wipe any excess with a cloth.

Hi Randy,
First and foremost: in real world practise there isn't such a thing as a too large top gap, the distance between the riser's end and the top of the bell. Way back in 2008 I tried to find out what the upper limit of that top gap would be. I ended with a distance of 4.5 feet and the thing (a modified J-tube) kept working without as much as a hiccup. The ceiling of my workshop appeared to be the limit here. So no worries here, I'd say.

I'm assuming you are talking about a batchbox rocket, these are very picky about a top gap that's too cramped. In practise, a distance equal to the diameter of the riser is regarded as a safe enough limit.

But then, why building an oven in the top of the bell, not very practical in my view. And having the firebox in the basement isn't very good for heating the living room/kitchen area.

May I suggest you build the whole thing on the first floor, the firebox' floor raised to about 2 feet above the room's floor and the white oven directly on top of the firebox?
Advantages would be all the heating is in the living quarters, one is able to keep an eye on the heater and the floor of the oven will be pretty hot. Not only that, by raising the firebox in the bell the oven will be in the upper half of the bell as well. With a carefully placement of the firebox, riser and oven combo the (recommended) top gap of the riser would be flush with the top of the white oven. Probably you need to build a foundation in the cellar though, to support the heater above it.

My two cents, helped by meddling with these heaters for many years.

If I remember correctly, it's 1/2" ceramic fibre board. The makeshift door was also out of the same material. This type of board tended to shrink quite  a bit, the bottom layer is probably up for replacement right now and other parts as well. This experimental heater is in function since september 2014.

Edit:
The white material turned out to be calcium silicate board, I just checked my posts from back then. At present, I'd regard this material as "handy to experiment with" but by no means suitable for a permanent installation. The door gave way a long time ago but there are more parts in there of the same material. Of course one could choose to use it anyway and do a rebuild every 5 years or so.

Hi Danijel,

Reading through your messages and seeing the pictures, I can identify three major mistakes and one possible restriction.

The possible restriction is the top gap, in my opinion this should be at least 8 cm instead of 5 cm. This top gap is the distance between the riser's end and the top of the barrel. In your situation, the top gap could be even more cramped when the barrel heats up and the top buckles in, restricting the gap further. Make it 10 cm and this will be fine, no matter what.

Mistake one is the heat exchanger around the riser. This shouldn't be there, a better placement would be inside the barrel and against the wall. The riser need to be as hot as possible, you are cooling it now.

Mistake two is the chimney pipe: this should be the same size as the riser. The riser is now 1.5 times larger than the chimney, cross section area speaking. Combined with the unavoidable elbows this is a serious restriction point.

Mistake three: in a well-built RMH the riser need to be made out of refractory material. Steel won't melt though, but due to high temperatures and lots of free oxygen it will corrode like mad. Even stainless steel won't be stainless in those circumstances.

Edit:
In case the pipe in the bench is also the small size, this is hampering the rocket's workings even more.

Scaling is similar to the straight or sidewinder versions. Remember, the original development model wasn't even a 6" but a 5" instead. I know of one that's an 8" workshop heater and it puts out a lot of power.

How to scale: take the published table and size the firebox and port accordingly. The short riser behind it should be the same size as the table suggest but the height isn't higher than the firebox top. The top box is as deep as the firebox and riser together, and a square cross section, as wide as the firebox. The stumbler halfway of the top box' ceiling, roughly as high as the port is wide. The end port 75% of the round riser's cross section, as wide as the top box and posioned about a quarter of the top box length, measured from the front.

Is this sufficient information?

And oh yes, in early July I participated in an art project  equipped with an 8" version in Belgium. The bare core was run with just one meter of large stove pipe on top to act as the chimney. It ran beautifully, despite being completed that same day and still soaking wet. Within ten minutes the smoke disappeared completely, producing the right sound and all.