Core definition help

I am preparing to cast a core and wanted to clarify what portions of it are referred to as what, so as to dial in my measurements.

Is the photo correct in that the burn tunnel starts after the feed tube and continues to the back wall, then the heat riser technically begins at the top of the inner core height of the burn tunnel?

Thanks so much for the help and all the invaluable info here! Lets get rockety...

Hi Prescott,

The locations you drew are roughly correct.
Some researchers measure from the theoretical center of each channel, which is probably relevant from the physics angle but very hard to measure in practice.

We tend to measure the total length of each part from the perpendicular brick faces that stop the tape measure.
So the feed is measured as you show it,
the burn tunnel is measured from the vertical feed wall all the way to the vertical heat riser back wall,
and the heat riser is measured from the floor of the burn tunnel up.

If you're using measurements that we described elsewhere (me or Ernie), that's what we would be talking about.

-Erica W

Thank you Erica! So really then what I hear you saying is that the portions of the core overlap, like so...

I am working on being patient and dialing in my measurements and ingredients BUT I am so eager to build and burn...

Thank you (and everyone else here) for making this so informative, helpful and inspirational!

Bumped to help a fellow member !! For this example, The Entire height of the Burn tunnel + one brick thickness ((a bridge Brick ) must be added to Find the
Total Height of the Heat Riser Which we can calculate as The inside Height of the barrel used, (33.5''~ish trust but verify) less 1.5 inches Minimum for a 6''
system and2 inches minimum for an 8 inch system.

Irregardless of the Type of firebrick used, if firebrick is used, leaving room at the top of the stack of mortared brick for a curved cap of Perlite and Clay Slip to
reduce the accumulation of fly ash on top of the Heat Riser Is recommended.

A question was asked about a Heat riser with total Height of 42'', this would give us a 'maximum' depth of the Feed Tube ALL inclusive of just 14'' to allow us to
cap the top of the Feed Tube and place bricks to channel air flow around our burning fire wood ! This IS a little short but Very Do-able ! As we want the Burn
Tunnel to be 1/2 the Height of the Heat Riser We are working with a very short 21''. Again very do-able, To change anyone dimention is to change them all !

Everything else being equal A tall Heat Riser Drafts well, and dense firebrick holds residual heat in the Burn tunnel and Heat Riser longer, making the RMH
Always easier to Re-start !

I would settle on Size to heat the core of my structure on 'the worst day ever', then on a location of the build 2nd, allowing for wood stored inside and ease of
carrying more in, giving some thought to clean-up and safety !

I would absolutely build a conventional/ traditional rocket mass heater, and if I wanted to play with the dimensions of my Burn Tunnel I would plan on being
able to disassemble and rebuild the Feed Tube end of my Burn Tunnel as the best way to dial in the maximum length a Burn Tunnel can be !

This is as close to a direct answer as I know how to Give ! Big AL !

Thanks Al, so am I to understand that the higher the riser, the longer the tunnel can be ? I would like to extend the horizontal portion and I'm willing to go up to 50 inches if I need to.
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On a lighter note, the temperature has dipped to about 27 F with a high of 30 F for 3 days in a row on Vancouver Island. I left Ontario to escape arctic conditions. My mustard greens have wilted and the kale is frosty. Flowery bushes have seen those blooms freeze. It may be a week before the garden starts to grow again. How have things been in the Rondacs ? Any snow ? We had an inch in December. It melted off the roads by noon.

Well, according to Peter van den Berg, it's all proportional. The size (CSA) of the feed tube, length of burn tunnel and heat riser all have to be matched.

We are having a cold winter here in Texas, as well.

Cindy Mathieu : Do you have a good link to that, I find Peter's work to be a bit of a Slug for me but I am trying !

Dale Hodgins : Ernie draws a parallel between the Height and Temperatures of the Heat Riser, With those very tall smoke stakes that were designed to carry
Oxides of Sulphur and Nitrogen far enough away so that they were no longer ''Locally Polluting '', and exempt from the laws then on the books !

With a good draw you will expect some of the Heat Riser to be in the Combustion Zone, If you can't see smoke or barely smell it, you have an exhaust clean
enough to run through a horizontal chimney and have exit temps at the base of the Vertical chimney around ~140dF~ !extracting the most amount of heat
and never worry about Creosote ( assuming you are starting with clean very dry wood )

First time I have had to deal with frozen pipes in about 20 years+ and we had an ice storm like took down the 765 Killovolt line Towers last time !

Peter's work is all documented on the donkey Proboards. I don't know of any specific links. When he gave us the specifications for the 3 sizes of burn tunnel, they included the length of the heat riser.

With a good draw you will expect some of the Heat Riser to be in the Combustion Zone

The Heat Riser IS the second chamber of the combustion zone!

Having two combustion chambers is the essence of burning wood efficiently and cleanly. The J-tube is just one possible approach to 2 combustion chambers.