My wife and I both work and maintaining temperatures in the greenhouse (future aquaponics setup will be built inside), with the frequent dragon feeding is a major setback.
What about this? I really like the heated mass part of the RMH, just not able to feed it as much as we need to. We get pretty cold temperatures in the winter (Southern Canada, near Detroit) and I need more time between feeds. My next idea is to remove the barrel and J tube portion and replace it with a semi efficient wood stove, and plug it into the existing piping that runs through the mass. Has this been done? I tried searching this on the forums but did not have any success. If there are threads please direct me to them.
Then I can run it hot to heat the mass and then dial it down but still have heat in the greenhouse, when we are not able to tend to it. Also, creating a water jacket within the stove to generate warm water for the future aquaponic system and running them in the growing beds would be an obvious plus.
I am not anti RMH, if fact my wife and I want one in the small cabin we are planning to build, but in the greenhouse with two full time jobs, we can't be tied to the greenhouse that much.
There must be some people who are in the same boat. What have you done?
I would suggest changing from the J-tube to a batch box for your combustion chamber. The batch box may not hold as much wood as a woodstove, but it will burn it more efficiently. If you can run it once in the morning and a couple of times in the evening, you may well be able to maintain the heat you need. A greenhouse is an ideal location for a batch box as you don't have to be around for extended periods.
What size (duct diameter) is the rest of your system? A 6" batch box is said to give equivalent heating capacity as an 8" J-tube, and an 8" batch box has been used to heat a 2000 square foot auditorium/shop in Montana (at Wheaton Labs).
Installing any kind of woodstove, if it is not a new super-efficient model, and running the exhaust through the mass, will cause creosote to condense and eventually result in a major "chimney" fire. You have no need to run a stove damped down if you have sufficient mass with stored heat. A batch box should take maybe 15 minutes to start and get settled to running, then it will burn unattended for about an hour. Ideally you would come back after that hour and shut down the draft or reload if needed. I just had the notion of a thermocouple-controlled setup that, once engaged, would automatically shut the air intake after the heat output falls below a certain threshold, i.e. down to low coals.
For very close to the same heat output of an 8-inch J-tube RMH, a 6-inch batch-box is the equivalent. An 8-inch batch-box will run super hot, dump a lot of BTU, enough to heat a small warehouse.
To keep a PvdB batch-box going continuously for hours at a time will require reloading it during the coaling stage, about every 45 minutes. Matt Walker has been working on extending the burn time of the batch-box out to several hours while retaining clean burning characteristics, details this thread:
Thank you everyone for the suggestions and all the information.
I like the idea of of a batch box but still it seems like more work than it's worth for me at the moment. I have been mulling this around for a few days now, and I have a few ideas. The reason I need to rethink this is because I want to have an aquaponics system in there before next fall. I am planning on incorporating the Jean Pain composting heater as well, to work in tandem with the wood heater.
Totally in my head right now and will stay that way until the summer when not needed. The rocket stove that I have created is working just fine for this early spring seedling start. I fire the rocket stove up for two to three hours before bed, and get some permaculture reading in as I do this. Overnight temperatures for the seedlings have not fallen below 60 degrees F yet.
#1 I have a fairly big cast iron stove that is in decent shape (with a bit of work to replace gaskets and the like), please see picture attached. What I think I could do in my head, is seal off the top exhaust whole (welding of course), line the stove firebrick, cut the legs off, and cut a 8 inch exhaust hole on the back to line up with the existing burn chamber of my already built rocket stove. In order to attach the stove I would cut the cob and feed tube off and then slide the stove box (without legs) flush with the opening of the burn chamber, and then seal the two with cob and surround the back of the stove with cob as well.
#2 Same stove but used differently. Open existing exhaust to the proper dimension of my burn chamber opening, flip stove onto back side, remove legs, and line up to existing RMH minus feed tube area. This means the stove door would be on top of the stove.
#3 Remove mass heater from current spot. Replace with a hybrid stove made out of the cast iron stove picture below. Remove legs from stove, build a firebrick heat riser on top of existing stove, insulate it with perlite or masonry fabric, use a smaller drum system, and plug into existing mass exhaust.
These are the three ideas that I am working on at the moment in my head.
It seems to me that one of the most attractive features of the RMH is the ability to provide heat to a living space over a long time period. One of the keys to this is that the living space is well insulated, making it easy to retain the heat from the mass. Typically, greenhouses will have very little or no insulation so they will need a continuous heat source to keep the temperature up.
I think the batch box RMH would be the best solution, but the mass will still lose heat rapidly and the fire will have to be tended. If anyone is thinking that an RMH will give the same performance in a greenhouse as it does in an insulated living space, I think they'll be disappointed.
Just my thoughts.
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It should be possible to convert and extend your existing box stove to a batch box rocket. It has been done before and as far as I am aware of, with a reasonable degree of success. The video is in French, can't understand most of it either but by plowing through it you can get a good picture how it is done. It takes the chore out of building your own door and door frame anyway.
Regrettably, those guys don't mention where they got the design from, the Creative Commons Licence idea isn't probably landed yet. Not even a link to the batchrocket website.
You would also look at switching your rocket stove over to burn either pellets or oil. having pellets just feed in slowly would keep it burning all day. Or I have heard of someone using used motor oil, that dripped into a burn chamber. I think they had like a tin can with screws in it to help splatter the oil.