A new outdoor Rocket system

[matt walker]

It's a work in progress, but I thought I'd share what I've been up to this weekend.

[matt walker]

Here's a few build pics. I just stuck the exhaust in the cob so it was lower than the barrel exit by a few inches. That ensures the chamber fills with hot gas before the gas finds the exit...



Cobbed in little stone walls to enclose the chamber...





Covered that with little truss sticks...



Cobbed over 'em....



....and lit it off!

[George Collins]

Matt,
Forgive my warm climate ignorance but what are the practical applications for having a rocket mass heater outside?

[matt walker]

Well, it's first and foremost a BBQ grill, outdoor cooker. Really efficient, fast, outdoor wood cooking unit. That was my primary goal. The rest is just window dressing as it were. Currently here evening temps are around 40*, and in the height of summer nighttime temps typically hover around 50* or so, so it's chilly. The idea was that I could cook food, and while doing that enjoy heat off the barrel and window below. After that, I thought, why not add a warm bench. The concept is that it doesn't have much mass, so it will heat up quickly, while you cook. It provides a warm cozy place to sit and watch the fire while cooking, and afterwards you can sit into the evening in front of a fire and be all cozy.

I don't think a traditional RMH build would be much use outdoors. Too slow to heat, too much mass, etc. This one is a bbq that shunts it's waste heat into the bench where it quickly heats the thin top and can be enjoyed during our cool evenings.

Also, I'm obsessed and needed to verify these concepts that are rattling around in my head to see how they worked. I think this kind of bench set up is a great solution to folks wanting this kind of system on a suspended floor. That bench probably has one tenth the mass of a standard system due to it's design.

[George Collins]

[GrahamB]

Matt you have me wanting one now. I'm wondering if you could bring that bench around in almost a full circle. I'm imagining everyone all sat round like a campfire circle. I really like the idea of that window too.

[matt walker]

Yeah Graham, that was essentially the concept, and I think for sure the system could push heat to a larger bench. But yeah, it's just about the best firepit ever. It never smokes in your face, you never smell like smoke, the flame is totally engaging to watch, and it throws a LOT of heat, both down low at the window and then the barrel is radiating at around 400* or more the whole time it's running. That doesn't even include a warm seat. My neighbor and I sat around it after that video for hours, and didn't even realize how cold it actually was outside until we moved away. It's really amazing. I love sitting around a fire in the summer evenings, but it's rare that I wanna burn that much good wood if I don't have a pile going that needs burning. This thing sips the wood, starts up in an instant, and is a bbq. I'm still just over the moon about this. If you get serious about building one I'd be happy to go into more detail on the construction here. It cost just about nothing, there's no expensive brick, almost no flue pipe. The only real costs are the perlite, the window, and a very small amount of 6" pipe for the riser and the vertical stack. I used some 10" pipe for the surround of the heat riser, but that could have been a piece of cardboard used to mold the material and then burnt off.

[Lollykoko]

I'm interested. When I'm at the farm alone I don't light the campfire, for various reasons. Using so much wood is one of those reasons.

[pa_friendly_guy]

Very interesting idea Matt. How does the BBQ work? Is it like a stove top heating up the stuff, or is there any smoke involved with the cooking?

[matt walker]

Well, it's not quite a stove top, as the flue gases do travel through the grill and past the food, but there's not really any smoke to speak of when the thing is up and running hot. Next time I BBQ on it I'm going to try putting some soaked alder chips on the clay diffuser in the bbq and see what happens. I will say that my neighbor and I cooked chicken and some onions and bell peppers on it the night I shot that video, and they tasted wonderful, like a good BBQ.