Rocket stove to heat 20ft container

Ok so I made this 4" rocket stove to heat my container. It's working extremely well so far with a clean burn and a cold upper flue. The container is being used as an entertainment room so we want quick heat from startup but a portion
Of heat into thermal mass to keep the chill off in case I fall asleep on the couch:-)

Any ideas on what material I can use to store heat around the lower portion of this stove?. Obviously I would like to keep the bell ( bottle ) exposed to radiate heat and keep my draft good. I was thinking of cob but I'm worried about too much cracking from thermal expansion as I have used a lot of scrap metal in it.

Cheers

Gareth

Hello Gareth,

I presume with all this metal in the design of this RMH that it is not meant to last very long? I am not sure incorporating mass would be warranted since the metal will not last but perhaps one to three season at the most, or did I miss something in the build? Is there refractory masonry in the design I am not seeing?

Regards,

j

Hi,

There is a layer of high alumina refractory between the 4" and the smaller box section.
Smaller box sect of the " j" tube riser seen at the feed area-this runs right up thru the larger box sect and into the bell.
Sorry I can't take a picture of it now it's assembled. I'm confident
I will get 15+ years from it. The riser is insulated all the way up to 2" from the top of the bell.

As for insulation I'm thinking of loose media perhaps... Sitting it in a steel box and filling it with media up to the top of the feed tube.

As long as the liner doesn't warp and impede airflow as it corrodes...
The layer of refractory is extremely thin if any where the round and square tubes are closest. I question how strong that will be for the future where it will need to hold itself up, as well as the obvious fact that it provides very little insulation at those points.

More importantly for now, perhaps, is your intended use. What climate are you in? How is your 20' container insulated? A 4" RMH will not generate a lot of heat compared to the typical small house/cabin 6" type, let alone a house-sized 8" system. Unless your climate is very mild or your container super-insulated, I don't see a 4" system being much use in the dead of winter.

Insulation around the base of your stove design is good! You want to insulate the burn tunnel. But you do not want to build mass around it, which is what i think you mean. You wanted mass for long term heat storage, by the sound of your post. You may want to INSULATE, the burn tunnel for a better faster hotter flame, and alter your exhaust, and gather heat in mass around the exhaust. Iooking at your design, i would personally make some sort of granite gravel gabion type tube aroumd the exhaust flue. Such as duct pipe that can snap close around the existing pipe, then fill with some kinda pea gravel.? Maybe tack weld another propane tank on top of the existing, filled with sand and gravel. It wouldn't bridge much heat directly from the stove, but still collect rising heat, not robbing the system of the heat it needs to function properly.

chad Christopher wrote:Insulation around the base of your stove design is good! You want to insulate the burn tunnel. But you do not want to build mass around it, which is what i think you mean. You wanted mass for long term heat storage, by the sound of your post. You may want to INSULATE, the burn tunnel for a better faster hotter flame, and alter your exhaust, and gather heat in mass around the exhaust. Iooking at your design, i would personally make some sort of granite gravel gabion type tube aroumd the exhaust flue. Such as duct pipe that can snap close around the existing pipe, then fill with some kinda pea gravel.? Maybe tack weld another propane tank on top of the existing, filled with sand and gravel. It wouldn't bridge much heat directly from the stove, but still collect rising heat, not robbing the system of the heat it needs to function properly.

Thanks for all the input people:-)
Ok so the riser is sufficiently insulated I think tho perhaps a bit thin. Worst case I can release the feed an riser parts by plasma cutting 3 welds and replace with a better one. One advantage of this steel design with loose media is I can take it apart and play around.

As the pic shows, I added tabs and bolted the unit onto a thermal blanket. This did improve the burn somewhat. It's very rockety!
Gravel/ Rock looks to be a great option for grabbing the heat around the exhaust. From what I gather keeping a good temp differential is good for the draw.

We are heading into winter now in New Zealand. My container will be spray foamed giving me Rvalue 6.0- which should be suitable for the auckland climate.

Looking up the Auckland climate, I understand your 4" system. It looks like winter nights average around 45F, with frost on just a few days. As all you really need is something to take the chill off, you should be fine.

Adding insulating blanket to as much of the combustion chanber as you can will certainly improve burn temps.