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Paul sits down with Justin to talk about the rocket heater he’s building, specifically a Walker Stove of Matt Walker’s designs.

Before getting to the rocket stove itself, going over the groundwork would be a good idea.  He has a 4 inch (10cm) wire mesh reinforced concrete slab, as per Walker’s recommendation (the builders weren’t convinced however), built on top of compacted gravel and easily-drained sandy soil so frost and water damage probably won’t be an issue.  Overall a good base, although it’d be better if it were a bit thicker and had rebar reinforcement instead.  

Justin heard on one of Paul’ previous pods that one of Matt’s previous designs had issues probably stemming from the lack of metal in the design that led to it taking a long time to start warming the room and is thinking of modifying the design to incorporate a thick steel plate on top of the bell to get heat out of it quickly.  Although just replacing the entire brick bell with a drum would be more effective, it’s too close to the wall to be safe without a suitable heatshield.  Getting one would allow him to reduce the minimum distance from a wall to around 4 inches (3 between the bell and shield, one between shield and wall).  On the flipside, Paul is going to be experimenting with different insulation materials such as sand and “superwool” due to dissatisfaction with the ceramic fibreboard due to high price and lack of actual insulative properties.  

A pebble-style RMH is also on the cards with a good point in its favor being the small dogs that might see fit to headbutt a hot drum.  The owners could also do the same, but for whatever reason people are less receptive to that line of criticism.

Relevant Threads

Podcast 517 - Red Cabin, Insulation, and the Bootcamp

Rocket Mass Heaters forum

Walker Stoves website

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