More generic through the wall system questions

I'm piggybacking on the other topic to ask about a slightly different scenario.  The cottage in my Kleingarten is unheated.  It has a nice roof and we're reluctant to put a hole in it for a chimney.  Also, it's tiny, so even a tiny woodstove inside would be overkill.  

I was thinking of building a rocket stove 3 feet outside the cottage for cooking.  In summer it would vent directly to a chimney, and in winter it would loop through a small amount of mass inside the cottage, then out again to the chimney.  There would not need to be a huge amount of mass, as the cottage holds heat very well - even body heat over night is enough to make it bearable by morning (it's just getting to sleep that is hard).  There's already a vent in the wall in that location for the previous owner's propane setup.

Is this a terrible idea?  Is there a specific type of rocket I should start with, or stay away from?

Thanks for any ideas or suggestions!

Would you be cooking a meal most evenings before you want the cottage warmed up for sleeping? If so, a rocket stove with a bypass and a mass option could work fine. Can you have any sort of roof over the stove and its feed location? That would make regular feeding of a J-tube reasonable in most weather. If the feed/loading area is going to be out in the rain, I think a batch box which can burn for an hour without reloading might be better.

In either case, I would suggest a bell bench extending through the wall rather than a duct looping in and back, to minimize added friction in the system. It would mean framing out a modest opening in the wall. I don't think you could use the propane vent hole for a duct anyway, certainly not without adding another hole for the other leg of a loop. I would consider making the bell low-ceilinged outside from the stove through the wall, then higher inside, so the hottest air stays inside the cottage. I would also insulate the sides of the outside bench where they serve no purpose being warm; the top could be a nice place to sit next to the stove in cold weather.

Glenn Herbert wrote:Would you be cooking a meal most evenings before you want the cottage warmed up for sleeping? If so, a rocket stove with a bypass and a mass option could work fine. Can you have any sort of roof over the stove and its feed location? That would make regular feeding of a J-tube reasonable in most weather. If the feed/loading area is going to be out in the rain, I think a batch box which can burn for an hour without reloading might be better.

In either case, I would suggest a bell bench extending through the wall rather than a duct looping in and back, to minimize added friction in the system. It would mean framing out a modest opening in the wall. I don't think you could use the propane vent hole for a duct anyway, certainly not without adding another hole for the other leg of a loop. I would consider making the bell low-ceilinged outside from the stove through the wall, then higher inside, so the hottest air stays inside the cottage. I would also insulate the sides of the outside bench where they serve no purpose being warm; the top could be a nice place to sit next to the stove in cold weather.

Thank you for responding!

--My assumption was that I would be cooking almost every night I slept there, though it gets dark so early in winter that cooking would probably more likely happen in the afternoon.
--The place I had envisioned the stove being built is not under the roof overhang.  A batch box sounds like a good thing to think about.
--A bell bench is a great idea!  I had figured there should be some insulation around ducting to protect against accidental burns, but a full bench would be very welcome in general.  Again, there's not much roof overhang there so cob wouldn't be a great choice - is there another material that you would recommend?
--Currently the "vent" is a screened section a couple inches off the ground, about 10 inches tall and three feet wide.  (I think.  There's currently a dresser and other storage in front if it.)  We could certainly cut a larger hole in the wall, but I come from the US and stick-built houses and am intimidated by these German stone buildings.  

Are there examples you could recommend for a bypass mechanism, and/or low bell systems?

Many thanks!

I was envisioning a 6" diameter hole, not a 3' wide x 10" high slot

I think what you have would be perfect as is for a through the wall bench. The outside section could have its ceiling flush with the top of the vent, while the inside section could be 4-8" higher.

I would recommend adding a tiny shed roof over the stove and bench. It would not need any heavy support if you can get corrugated metal or polycarbonate roofing material. Just angle it to drain in an appropriate direction. I don't think any part of Germany has a desert climate where you can expect dry weather most evenings. It would be easier to cook if you don't have to contend with rain or snow.