Cookstove + Masonry Heater Hybrid

Here is a little more detailing on the concept sketch, also showing my hope that we can include a hot water heat exchanger that thermosiphons to a hot water tank.

Here’s the SketchUp file if anyone wants to play around with it or insert it into a home design:

Cookstove and Masonry Heater Hybrid (SU v2021).skp (1.7 MB)
Cookstove and Masonry Heater Hybrid (SU v2017).skp (3.6 MB)

The next step is to start drawing more technical sections showing the flue paths.

Anyone have any votes about how best to name this project!?

  • Cookstove & Masonry Heater Hybrid
  • The “Power Station” Heater
  • The “Mother Ship” Heater

0 voters

Suggest other names and I’ll add them to the poll.

Max, I have always found the 9"wide or so firebox of most cookstoves to be limited on how many channels you can add on to them. So we normally will use one of our standard 13"w x 18"d fireboxes and add a cookstove top above the firebox and then vent the exhaust out the side of the firebox into a down draft channel and a large bell or just into a large bell. Kinda like the MHA workshop we did 2 or 3 years ago. Below are 2 photos of a simple bell on the side and a more complex bell.

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@SolidRock, it’s an honor to welcome you to the forums. For those who don’t know Eric, he is one of North America’s most accomplished masonry heater builders.

Indeed, I am planning on a slightly larger than normal, for a cookstove, firebox and importantly for the main combustion route to lead into a significant heat riser which I am hoping will produce the kind of thrust that we see in rocket mass heaters. I should have some sections done within a week so that the inner workings will be more understandable and open to critique and response.

I look forward to this. I will have to look at getting a link up on my website for this forum so that others can see it, learn and contribute.

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A post was split to a new topic: Joseph Crawleys Multifunctional Heater

The Heat n Eat (alator)! But in all seriousness, i’m really looking forward to seeing your design come to life in April. It reminds me of the first masonry heater I ever saw, at Granja Valle Pintado back in 2011 with a small water tank up above for hot water heating and a lounge-y heated bench… I became infatuated with the idea of hot cob!

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Hey, hey! Welcome Jim! Another great heater builder joins our ranks!

Indeed, once you get interested in masonry heaters, especially from first-hand experience, that interest tends to continue strong.

I love the “Heat n Eat (alator)”! Just now realizing I can’t change the poll after it has been live 5 minutes.

Yes, looking forward to further developing the design. Stay tuned!

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Hi all! I wanted to post some drawings before the week was out. Here are two sections that I have begun to develop for the inner workings of the stove. It still needs a good bit of refinement and a couple more sections to fully describe its function.

This is my first shot at describing the combustion chamber and the two possible pathways that gases can travel as they exit. It still needs some effort to make it “cozy” for the fire…

And here is a first sketch of the main heat exchange battery. The oven and hot water coils still need to be detailed in this section…

Stay tuned for progress next week!

How’s the design coming along?

Hi all. Here’s an update of what I’ve been working on…

The first is just a section summary graphic so that the sections can be understood in the context of the overall project:

I developed a first go at the flow pattern at the level of the bench, which also includes the ash collection area.

I was surprised at how complicated the entrance into and out of the bench ended up being and am hoping I can simplify it. It is a constant goal of mine to keep things as simple as they can be.

I started thinking that the firebox design on the right, with the inclined exit, would result in better organization of the fuel, fire, and its byproducts. The down side is that it complicates the construction some.

I would love to receive feedback on any of these ideas/drawings. It really provides energy to the project to know that people are interested and there is a dialog happening. What do you think of how this is developing @Canyon, @mheat, @Tallgrass, @SolidRock?

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Max, the bench is looking quite long for the size of the firebox. I doubt it would balance out in the Austrian heater calculation program. I would suggest cutting the bench length in half, mainly due to the size of the small firebox.
The angled firebox back is not needed.

Looks awesome brother! Interesting fireboxes. Are you considering a port or is the firebox exit full riser size?

Thank you for the feedback.
How would the Austrian heater calculation program account for an even smaller fierbox like the one linked below easily powering a bench with a lineal run of 18’ (6 m)?

I am thinking the Annual Meeting is a good place to test things out and when it’s been cold, the heated bench has been appreciated.

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Looking good Max! Where is combustion air being fed? Through the door? The classic-ish design of the rocket stove horizontal “burn tunnel” and 90 degree entrance to the riser was the original point of mixing to induce the most turbulence and combustion. I wonder if the 45 degree angled exit into the riser smooths out the transition and it if wouldn’t be worth annunciating the initial throat to more of a point like Peterbergs tripwire brick to really enhance mixing in the 45 degree angled run.

Also, on a selfish note, whats the software you are using for these structural design prints, looks very clean and welcoming way of presenting a design to a building department.

@Tallgrass, thanks for your reply!

Well, I imagine it potentially coming in from three different locations… either from one of them exclusively or some combination of the three:

I have just always been so intrigued with the efficiency of the cigarette-style end-burn we have witnessed in an original rocket mass heater. This is an effort to allow for more fuel at a time with a glass door for viewing but maintain some of the synergy and symmetry offered by the original design….

This is a good point. One of my personal goals for this project was to take the time to review what had been developed and documented in the other forums with regards to batch box development. Your response forced me to begin that review process of the “p-channel” and the “tripwire”. I will see if I can continue design development to document that area that you and @Canyon are talking about.

Nothing selfish about asking a question in a public forum! You might be surprised to know that I am doing the design drawings in SketchUp. It is known for its 3D modeling features but I have found myself using it to draft in a more traditional way. I find sometimes when I am 3D modeling that I get lost in the specifics of each unit in a brick-by-brick approach instead of being able to design more globally. I use the companion program LayOut which is part of the Pro suite to add our logo plate, labels, dimensions, etc.

This is exciting. While I can’t speak to any of the technical specs, I think the concept and the aesthetics are coming along nicely. I like the added bench. The one masonry heater I have seen in operation had an air intake, I believe, right inside and below the door, so that it kept the firebox door from getting dirty. I don’t know how much that adds to the design complexity :slight_smile:

Air intake and door glass air washes are ripe for another topic! :slight_smile:

I spent some time this last week detailing the oven and the hot water heat exchanger…

I am going to update the original post with the full drawing set, where we are at now. I think that the original concept has mostly been flushed out at this point but there are still many details to continue working on.

One example is the switch from firebrick shiners to splits to accommodate the flow around the oven. I had imagined this from the start but seeing it drawn leaves me feeling that the portion of the wall where the bypass damper is mounted appears weak.

I also know that I need to draw a section from the front exploring the second route of the combustion gases across the cooktop.

This is a creative process and it is full of the excitement as well as the uncertainty of any such endeavor.

Here is a summary of the hardware that Firespeaking supplies that you would need to build your own version of this project:

The one item that we are limited in stock on is the cooktop. We currently have 10 in stock so if you are following this project and interested, now is a good time to make your order.

Here are two additional drawings…

The cookstove formation seems like the weakest part of the whole design. @Canyon , you had asked about the “port”… I’ve sketched it on the right. It’s currently roughly 6 w x 6 3/4 h. Thoughts on recommended size?

One of the biggest dilemmas I’m meditating on is that their is a confluence between the longer flow through the vertical masonry heat exchanger and the cookstove flow as they join towards the bench that I feel could be problematic in that it might cause a short circuit of the longer path and disrupt or weaken the more “rocket” type combustion we are trying to create when not in cooktop mode… Any thoughts out there? I will be thinking about it.