Date: Sun, 12 Jul 2009
From: Alex Chernov <alex_stovemaster(at)>
Subject: rocket/bell experiments
To: Norbert Senf <mheat(at)>
Cc: Dave CCHRC <dave(at)>

Hi Norbert.
Just read your report completely. Very interesting effects of allowing gases a time for buoyancy effect to take place.
I think that you experience problems with starting and maintaining the fire for the reason that you got rid of the most important part making the rocket stove work - the heat riser. now, you lack its stack effect creating constant negative pressure at the firebox exit. my proposal for modification is to make a square (as close to round as possible) heat riser channel inside just behind the exit as in normal rocket stove, and place insulating board deflector just below the capping brick right over the heat riser to protect brick and to even out temperatures. I think that you should not need additional separations inside the bell, but also it would be interesting to place firebrick columns on its long edge right at the middle of  the channel (dry)  with spacing of about brick length to see what effect it has.

also, on another note, i was thinking about making the firebox throat vertical instead of horizontal and shifted towards one side of heat riser to induce better gas rotation in the heat riser.( it seems better to direct gases out of the firebox the way gases want to go since gases move in spiral motion in such channel) One problem though that it will make exit higher therefore allowing gases from upper portion of fuel to escape earlier - potential for dirtier burn. this however might be compensated by better mixing in the heat riser. it also would be interested to experiment with introducing secondary air to the riser right past the firebox throat...
I think that with good riser and such placement of the throat, the stove should tolerate taller firebox that would allow for larger loads... just thoughts.

Hi Alex:

Thanks for your comments. I'll post them to the rocket page.

I'll give the heat riser a try, to see how much difference it makes. The "unstartable" version certainly serves as an extreme reference point.

Check out today's post. Yesterday, I changed the firebox to an underfire grate, exiting directly into the bottom opening.
Worked extremely well. Once the stack was up to 150F or so, lots of draft when I pulled the door plug to reload.
So, in this iteration, it works without a heat riser. Kind of a side-draft rocket, rather than a down draft rocket.

Unfortunately the O2 sensor on the Testo seems to be toast (it has about 300 hours on it over 3 years), so I've got to replace that before I can get any
efficiency data.........Norbert

Norbert Senf---------- mheat(at)
Masonry Stove Builders   
25 Brouse Rd.
RR 5, Shawville-------          
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