I built a (somewhat) portable collapsible ceramic fiber board rocket stove deck and patio heater / stove / pizza oven with a vacuum formed ceramic fiber 6" riser. This is designed to be easily taken down and moved but the 2" low density ceramic fiber board insulation, while being easy to cut on a table saw, is a bit too brittle for frequent assembly/disassembly. I built this in my garage in PA, took it to a camp out with about 40 friends in Michigan and fired it for the first time, dissembled it and came home to PA, then took it to a friend's in New York to experiment with the pizza oven.
Barrel is cut from a standard 55 gallon barrel at 25" and the pizza oven on top is about 12". Riser stands about 12" into the 25" barrel on top. Barrel top temps hit around 740 degrees F via infrared thermometer, and pizza oven (uninsulated) hit 500 degrees on a Bacharach flue thermometer. Secondary air is introduced via a 2" x 1" channel I made with a router in the bottom ceramic fiber board under the firebrick liner and introduced with a 2" black iron pipe that goes through the firebrick about 1 1/2" from the riser. See photos.
It has satisfactorily survived about 1500 miles of traveling and being assembled and disassembled three times now but I don't think the ceramic fiber board would hold up to repeated assembly and disassembly.
This could be used as a deck, patio, backyard, cabin, hunting tent, ice fishing hut, or emergency heater / stove / oven.
The bottom, left and right sides of the firebox are lined with firebrick splits. A thin plate of stainless lays over the secondary air groove under the firebrick to seal it better. I don't plan to add any more than that.
I haven't weighed it but I figure total weight is 100-120lbs.
I finally got a chance to do some more controlled tests with this stove. I sealed around the door frame with black carbon felt as a gasket and used 8' of six inch chimney pipe. For fuel I used a twelve pack of small compressed sawdust firewood bricks. I started the fire at 4:15pm. It stopped smoking and the flue gases were clear within 5 minutes. The barrel top hit 760 degrees within 25 minutes and the pizza oven hit 600 degrees (during prior burns the pizza oven only got to 500 degrees)..
Interestingly, using regular firewood in the past, it was burned down to ashes within an hour and a half.
I walked away and made dinner after an hour, but when I came back after two and a half hours the barrel top was still 300 degrees. I opened the firebox to find the compressed sawdust logs still burning and only half consumed.
In retrospect, I think my black carbon felt gasket around the door frame may have limited the primary air entering the firebox, slowing the burn, because I noticed some smoke when I walked away after the first hour. I'm going to have to take a closer look at that tomorrow.
After two and a half hours:
I threw in a small piece of cherry firewood and barrel top temp got back up to 470 degrees.
Thanks! I learned everything by trial and error and watching various YouTube videos.
I opened up the primary air path and tore apart the burn chamber today. I created an expansion chamber where I had previously had the vertical riser. I then moved the vertical riser to the left front of the box and cut the side of the vertical riser out next to the expansion chamber up 6" from the floor.
This is vaguely similar to the Walker Riserless core. This sort of creates a combination expansion chamber/ horizontal riser then immediately a true vertical riser. I forgot to take a picture so I have to wait till it cools.
I already got 15• hotter in my pizza oven, 615• after 45 minutes. Stove top temp was increased, up to 776 •, an overall improvement of 36• from the initial tests.
Burn times are definitely longer with the compressed sawdust fire bricks. After one hour and ten minutes pizza oven was still 500 degrees without any insulation and the door still open. At two hours it was still 400 degrees, and stove top temp still 575 degrees.
About half the compressed sawdust fire bricks were still burning.
Edit to add:
Here's a picture of the simple expansion chamber/vertical riser layout I came up with:
At four hours after light up and with only the original load of firewood bricks, the pizza oven is at 315• and barrel top temp is 386•.
What kind of temps are people getting on top of their barrel 4 hours after lighting a batch box with no refills? Is it possible my air supplies are too restrictive, prolonging the burn? The smoke from the chimney is crystal clear.
I did burn 1/2" x 3" pine boards and packed the firebox, leaving air channels between the stacks. It didn't get near as hot (620 barrel top within 20 minutes of lighting fire, pizza oven 450 an hour after lighting fire) or burn near as long.
Barrel top was down to 340 at two hours and then it rained But there was still fire in the firebox at 3 hours after lighting (last photo.)
I rearranged the fire path again and once again using 12 blocks of compressed sawdust logs the barrel top got 90 • F hotter, up to 865• from 774• (even though outside temps have fallen to 65• this evening, and prior tests days were hot and sunny in the mid 80s.)
You can see the strength of the natural draft here through the small mica glass viewport in the side of the firebox. The flames are moving/drawing so fast they're horizontal.
Thanks! This was my first prototype and I'm using it as a workhorse to test different options working towards a vacuum formed ceramic fiber rocket stove core. Although the final prototype will have some significant differences, I wanted to be able to point to the prior efforts and documentation so people know it will actually work. It's easy to make claims about something but I need to see concrete results behind such claims and I suspect others do too.
I finally had a chance to run a batch of hardwood firewood, a combination of 6 pieces of ash, oak and cherry. The wood was well seasoned but unfortunately uncovered and with recent rains it didn't perform much better, hotter or longer than the pine boards, with approximately the same barrel top temps and duration of burn, three hours and 560•.
The compressed sawdust bricks still hold the record with almost 6 hours burn times and 865• barrel top temps. Wood stove users don't relate extended burn times with the compressed fire bricks but they sure seem optimal in this rocket stove application and they are the only way I can accurately compare changes in firebox and riser geometry and primary and secondary air adjustments..