chaz van

Thanks again, Glenn.

Yes, I agree real results likely considerably less.

Now that I think of it I grew up in a century old drafty frame house without insulation that my father had retrofitted with a wood burning forced air furnace. It was in a relatively mild climate but consumed 2 cords of wood a week in the coldest weeks. Under the right conditions/equipment, I could cut, load and haul about 4 cords of maple in a day. My second floor bedroom single pane window would accumulate ice on the inside on the coldest nights.

I used chunks of wood in the gassiffier units I built.  Had only a very small door for loading.  Again, the metal burn chambers burned through after a relatively few firings.

The current building does have forced air gas furnaces, one for each end.  When I first tried them, concluded it would cost $70 a day of propane, which is now even more expensive.
The problem with a rocket stove is that I have not figured out how to relatively simply get hot air into the existing forced air system. I also am really hesitant to run two wood burners for the building.  Up until this year, I have been using a central triple horizontal wood stove with an open collector above and ducting/fans pointed at either end. Again, the problem with this was dirty burn and chimney fire. I have thought of an external boiler with heat exchangers in the forced air systems but the cost of commercially available systems has been more than I have been willing to swallow.

The video added to this thread is interesting. It looks complicated and expensive. I have not figured out where the flue exhaust is on it.

Thanks again for the response thoughts.

Glenn,
No problem with that but I am trying to go the other way. Most specifically at the moment, how many BTU/hr could you get with continuous burn of a 6 or 8" batch box rocket stove?  Don't want mass in this case, just fast heat. I am currently working on determine how many BTU per hour are needed to keep she space relatively comfortable. Once I have that in hand, I need to figure out what size BBRH I need.

Where I have seen KW mentioned, Is that kw/hr if continuously fired? Generally noted for 2 firings a day so does that mean 12 hours per firing, in which case one firing would last an hour so 12 times the kw would be the KW per hour rate?




































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Just found this old forum.  I have an 8" Dragon burner which is vertical feed.  I have generally found 1.5 inch (2 by 2's) work best in it.  When I have tried large diameter is does not burn well/goes out.  I am talking old dry lumber so I am surprised about single 5 to 8 inch working. My general experience with wood fires is that it takes two or more burning pieces facing each other to burn effectively.

I tried burning wood chips in my 8" Dragon J-tube.  I set up a hopper with a variable speed conveyor that dropped chips into the burn column. I did not get to play with it enough to work well.  I could not get it to sustain a good flame. I tried a variety off "grates" in the burn area but They never did an adequate job. The chips tended to build up and smother the flame even though I slowed the delivery way down.  I think there may have also been an issue with moisture content at the time. Never got around to using one of my moisture meters.  I have burned long 2 by 2s in it (6 to 9 feet). a few stopped feeding and fell over/out. It took some external structure to keep them vertical.  Gave up on that and have just gone to cutting 2 by 2s to about 2' lengths.

Just found this forum.  Enjoyed Ericas's old dissertation.

I have been messing with wood heat for several decades. Started out with catalytic fireplace inserts.  Somewhat short life the the catalysts and erosion of the steel parts inside.  Also once put a stainless flex liner down a masonry chimney in Eastern Canada. Built and used numerous horizontal barrel stoves (VogelZang components)--1, 2 and 3 barrel.  Two barrel were claimed to be about 200,000 btu per hour and heated up fast. The 3 barrel was really poor on drafting (added a draft inducer in one case) and was really bad for soot buildup (had to clean upper barrel and chimney a couple times a year). Had a near catastrophic chimney fire one winter when I was not there to see that it got cleaned.  Experimented with gassifier burners for  a while. Got up to 300,000 BTU per hour heating water  and ran hot water through garden hose to truck radiator with fan behind it inside but metal burn chambers did not last very long. Tried to repeat with refractory materials but They (flue liners and cinder blocks) kept breaking.  Never got a chance to try building fire brick burn chambers.  Got a Dragon 8" cast core and built a steel box around it insulated with vermiculite. Put a 3 barrel bell on top of it has shop had a high ceiling.  Dragon claimed at the time it was good for about 80,000 BTU per hour. It was fairly expensive at the time. Don't know if it is still available or how much it would cost now.  Downside is it burns through the small wood charge in a hurry.  

My experience with the the J tube rocket stove with no mass shows a bell exit temp of about 175 F.  I don't see why there would be any difference between a massless bell and masonry bell if both are sized properly.  I had never considered chimney stall and never knowingly experienced it although I have had a few rare back draft experience that it might explain. I have never had a draft problem with Dragon 8" unit. The chimney comes out directly under the bottom of the bell and goes straight up about 16 feet. Have not fired this unit enough over the years to think of checking for buildup.  Probably only averaged a couple firings per year.  Don't remember the temperature profile o0f the 3 barrel bell--and not currently at that location.

I would think the extremely dry air where my stoves are located would do a pretty good job of soaking up any moisture int the flues warm gases.

I make sure that I have at least one working CO/Smoke detector in the vicinity of any indoor wood burner.

Not specifically stove related soves but I am frequently looking for components to use in a manner not originally intended for. Saying it is for an experiment generally gets rid of the "whats it for?"

Has anyone made a chart or list of BTU/hr for different types/configurations of rocket stoves?  I have seen what appears to be KW or KWH per day from a couple firings per day but I am not sure how to convert that to BTU/hr for continuous firing which is how most heating appliances like gas furnaces are rated.

Thanks Glenn. Some how I missed the 3 barrel build.  I have an 8" Dragon core with three vertical barrels in another building. The downside is it does not hold much wood and requires frequent feeding to warm its space much.

If I interpret Peter's data correctly, an 8" system should support up to 5 barrels.  A 6" 3 barrels. The challenge here is that my expensive newly installed triple wall stainless flue is only 6". I do have an old 6" flue next to the old one so I think I could run the exhaust of an 8" system into both to get the equivalent of an 8" flue.  The exhaust temp of a multi-barrel bell should be cool enough and clean enough not to worry about chimney fire. Not sure yet if I have enough ceiling height to stack 3 barrels.

I am currently experimenting with a 25 kbtu indoor propane heater to see how much that heats the area when cold outside.  Hopefully the Btu requirement versus temperature will scale relatively linearly.

More recent situation.  I need to heat about 60,000 cubic feet of space quickly.  I have seen several images of 4 barrel  batch-box rocket stoves that seem to have this general aim. However I have not been able to find plans or detailed information for them. Can anyone please direct me to such?

I have spent a lot of hours searching but have some physical limitations that limit my efficiency.

a couple points. the building in question was originally heated by a pair of 110,000 btu/hr NG forced air units.  Assuming 80% efficiency, it would take about 30 pounds of wood per hour to get  a continuous 200,000 btu/hr (if my Math is correct).  The insulation has been improved considerably since these NG units were used (NG no longer available on this site). At this point I am more interested in heating air than mass. Has anyone ever tried sending the output of a rocket stove through an NG heat exchanger?  Seems like this might be a good compact way to get heat from the gas stream into a room as opposed to a barrel, bench or masonry bell.

Thanks to all for your input.  If I did not currently need the heat I would consider a batch box build.  As noted,  I have adequately heated the space in the past with a bit over 2200K btu/hr.  I have short ducts with fans that point to either end from the center where the stove is, with a collector above the stove.  The building is stick frame. I added blowin fiberglass under the floor and above the ceiling with double reflective foil over air bubble to hold the below floor insulation up. I had 2" rigid foam added to the outside walls and covered with reclaimed aluminum siding.  The existing stove has a simple steel sheet for the top with the fire box directly under. The flue exits at the side top of the firebox. The top gets to 700 to 800 degrees F.  My intention was to run a P-tube across the stove top for preheated secondary air and bring it in right at the exit from the fire box. The secondary burn chamber would be immediately after the first chamber exit. Not sure about having it vertical versus horizontal. The primary objective is to cleanup the exhaust but it would be nice to recover some additional heat. I have not yet figured out how to do that.