speedy Hatfield

Thanks Ronnie,
seeing the the vid seems to have cleared a few things up for me.

So, the way I see it now , and ho it differs from the kang is that it has the flue inside what is effectively an expansion chamber immediately after the fire box
The flue , being insulated becomes superheated above flashpoint of volatiles (which otherwise become smoke) and allow complete combustion.

The gasses have room to expand in the drum, radiate heat then contract as they cool.
The contraction adds to the flue effect but in reverse.

It sounds more  analogous to a Jet , or more specifically a Ramjet than a Rocket .

Like you said, similarities with Russian masonary heater and Kang combined , yet still different in its own way.

maybe there are Kangs without a flue, I've not seen many to comment.
I've always envisaged them with a flue and to have one without it would be prevent it from even working.

When you talk of 'heat riser' you do mean a flue don't you?

I'm sure there were/are very efficient systems already.
Smoke is an obvious sign of inefficiency and easily addressed.
introduce more air for a complete burn.
this could be done by redesigning or increasing flue length for more drawing of air.

Choice of fuel can play a role here also.
bundles of small sticks would be better than logs as there is more air and they burn fast and clean.
the efficiency or the system is also in capturing heat quickly, storing it and giving it up slowly.

another advantage to using small sticks is that they take less time to grow.
ie. a shorter solar energy cycle- compare 1-2yrs for stick, 5-20 yrs for logs and many millions of years for coal ,oil or gas.

I wouldn't consider metal in the design as it will have too much movement over temp variations, except maybe in the vertical flue, and this will damage mortar joints or earth construction and cause it to leak.

metal transfers heat well and wont store it well.
it can also burn out , esp. with high temp fast burns.

masonary construction is key to storage of the heat.
The horizontal flue (heat sink) should be horizontal or slightly inclined.
any decline will interupt flow and efficiency.

If they're smokey, they're not being used properly or not designed properly IMO.
 

A Kang, yes

I just saw this thread and started to trawl through the posts looking for any reference to a Kang.

all the while  thinking 'They're trying to reinvent the wheel here'.

The Chinese had them around 400 BC.
A simmilar technology was used by the Romans to heat buildings, especially bath houses,
but was lost to Europe after the demise of the Roman Empire

Kang furnaces are still used in rural China today.
acording to one study 85% of homes in northern China over 65million of them in use.

Some points to consider in the design:-
-draw air from outside building for burning

-combustion/expansion  chamber should be about 3 times cross section area of the rest of horizontal flue for more efficient heat transfer.
there will be  contraction of gasses as the heat is pulled out of them as the travel through the horizontal flue.

-make  3 or 4 180degree turns in the Horizontal flue to scavenge maximum heat and allow for wide area rather than long.

-at the base of the vertical flue there could be a door to open in order to a build a small fire to start the flue drawing air just before the main burn is ignighted.

- the kang can be built as a raised section above  floor level or as a bed
...or it can be at the same level as the floor and the side loaded burn chamber accessed via a sunken section below floor level.
- a side loaded burn chamber may be easier to clean out than a top loading one.

- I'd definitely build it all with brick and the burn chamber with refractory bricks and cement if possible.

-if  metal was used the expansion and contraction would need to be taken into account , but it would also likely burn out pretty quick and just interfere with the function of it.

Thats how I'd start anyway.

I've been wanting to make a Kang for many (about 20) years but haven't had the opportunity or need... yet.

Hope this helps anyone wanting to make one.
post some pics if you do