The fact that you are not getting flames into the riser tells me that you perhaps don't have enough draw going on.
If your J tube is not rounded at the back end (where the riser starts) then you will not get a fully efficient burn.
If you have not found this site yet, Donkey's proboard site Then this link will get you to the best information on Rocket stoves, Batch stoves etc.
The folks there are really super with posting their experimental results and there are charts/ formulas/ spreadsheets on every measurement for most sizes of Rocket stove.
If your riser is long enough, then you should be getting a temperature of around 1600 degrees from a burn. The riser for a 5.5" J tube should be around 3 feet tall and 5.5" inside diameter. peterberg batchbox dimensions
One other thing to check; make sure your dimensions on the J tunnel are correct or at least very close to correct, these are really important to get a fully efficient burn. Also, do your checking at night so the flames are easier to see, a P channel will also help get a complete burn and improve efficiency.
J Black wrote:Simple and general question. Sorry if it's been spelled out elsewhere, but I haven't been fortunate enough to run across it, if it has.
When testing the combustion unit of J tube (in my case a 5.5" system) in a rmh/stove, how high should the visible flame be coming up the heat riser?
Is it a fail if the flame isn't shooting out the top. I've tried a few variations and the flame, at best, only just enters the heat riser.
I was concerned with my stove not being hot enough to "work properly", so - simple idea - get a piece of copper water pipe and lean it up inside the heat riser . . if it melts the copper at full burn, you are hitting at least 1,984 F - or so.
Second test - drop in a pop can. If it melts at the mouth of the burn chamber (where you can see it) then you are hitting at least 1,200 F.
I tried the lean too idea with welding rods, but they don't really give a good temp "picture". . .
To do a great right, do a little wrong - shakespeare. twisted little ad:
Switching from electric heat to a rocket mass heater reduces your carbon footprint as much as parking 7 cars