Over the many years of boiling sap in a home made backyard evaporator, I would often think about all that heat coming out

of the top of the stack after it rushed under my pan.  A LOT of heat !  Then I learned about an amazing heat storage device,

called a Rocket Stove Mass Heater.  It’s twice over awesome.  On the one hand it’s super efficient at combusting fuel.  And on the

other it stores all the heat in a very large mass of clay and stone, slowly emitting it back into the house over time.  See photos and diagram below…

With some consulting from my friends Erica and Ernie, I incorporated this design into my maple syrup operation.  What that does for me is on very little wood

I create an inferno underneath my pan from that rocket stack inside the barrel.  Then the heat comes down the inside of the 55 gal barrel out the exhaust pipe,

wraps around the inside of my maple syrup shack, heating me and my future cob bench !

The Slideshow above shows how I put it together with reused materials from my local ReNew center.  Sealing all the joints and gaps was done with a clay, sand and straw mixture, all locally obtained for free !  The Perlite is non combustable insulation.  This insulates the heat chamber, keeping the temperature up.  The 4 ft heat riser is also insulated.

Well ?  what do you think ?

Comment below !

To a Resilient future !

7 replies
  1. Erin Maile
    Erin Maile says:

    Aloha mai Mark, I’ve been looking into the building of a Rocket Stove and love that you’ve done it! Can’t wait to see it in action. Let’s make a plan to share a meal soon!

  2. monique
    monique says:

    This is great!! I have always been distrubed by the amount of heat loss as well. And I have been designing an outdoor hot tub lately, so perfect timing! I am going to do this except on a large scale and put a round stock tank “bath tub” on top of it for future hot tub soaking! Thanks for sharing!

  3. Sam
    Sam says:

    Amazing idea, love the gusto! THe pictures could use captioning or a more detailed explanation for aspiring others who aren’t as fluent yet in this type of engineering.

    Thanks Mark!

  4. Steve Voorhees
    Steve Voorhees says:

    This is an ingenious pursuit of efficiency and the focused flame on the pan seems to be a good concept. In the i970’s, when I tried to keep up with my back yard Rube Goldberg evaporator set up, I obsessed about the loss of heat out of the stack and I sought to employ my waste heat to preheat another pan of sap on an upper level so that the exhaust was further cooled on it’s merry way to the out of doors. I found that further efficiency came from making a hood over the evaporator which kept the heat more contained on the pan. Of course it would create ALLOT of condensation which needs a gutter around the edge so that the reconstituted water did not drip back into the very pan that I was trying to remove water from; but needless to say, the water condensate was basically distilled water that had a faint maple-ish aroma.
    But of greater concern to me in your design is:
    (1)- Cement blocks decompose and crumble with heat in the same way that heat in the Kiln which cooked the original limestone (That cement is made from by cooking limestone long and hard until the bonded water molecules are driven off; It is pulverized and then mixed with water, sand, and gravel to make concrete which is stronger than limestone but, still vulnerable to heat. I discovered this because my first evaporator firebox was concrete blocks supporting the pan which had crumbled by the end of the season.) A better choice would be firebrick or large flue-tile. (It’s funny how futile became flue-tile!)
    (2)- OF SERIOUS CONCERN: perlite is now considered carcinogenic, especially the dust. It was a traditional component of potting soil for it absorbs and holds water without compacting or adding weight but I doubt it is sold for that purpose anymore. I believe it is no longer approved for house insulation although it was used in walls and ceilings because it poured easily into hard to reach places. So beware in handling it without a respirator at least!
    Otherwise: Bubble, Bubble, Bubble goes the pan…
    Furnish sweeter music for the season if you can…
    See the rolling billows; watch them ebb and flow…
    No sweeter joys on Earth, we sugar makers Know….
    (Trad. I think) -there are many verses too

  5. Steve Gabriel
    Steve Gabriel says:

    Hey Mark;

    This is cool to see — I built one many years ago with the same thought in mind – but after prototyping was convinced the heat output wasn’t comparable to the fire flames directly touching the pan – we were boiling ~50 gals at a time then. I’m starting to tap our new sugarbush of 70 trees and would love to hear how this works – have you tried a boil yet?

    cheers, Steve

    • markmorey
      markmorey says:

      the design needs an adjustment, basically the inner pipe needs to be taller and closer to the pan.

      I started rebuilding it. In the meantime I created another evap operation for this season.



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