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Heater size and loading tradeoffs

Posts: 45
Location: Oakland, CA
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So I had been wondering about the difference between 6" and 8" rocket mass heaters, but now that I've been running my 6" system for a while, I'm realizing there's a lot of variability in how I run my heater. I can load it up, maximize the amount of wood and the density of the wood I have loaded and get the hottest burn possible. With a 5" gap from the top of my riser to the top of my barrel, I've hit 760 degrees on the barrel top. More often, I spread out that same load of wood, burn my heater at 1/2 to 2/3 capacity, get a barrel top temperature of around 550 degrees and the wood lasts for 2-3 hours.

So every heater has some maximum amount of wood it could burn/hr. Is the goal always the hottest fire possible? When I run my system at max capacity, the exhaust leaving my system is substantially hotter than when I run my system at half capacity. I'm guessing there's some tradeoff between burn heat and burn efficiency and system heating speed or heat a system can receive/hr. At maximum wood burning load/hr, I'm guessing a lot of systems can't process that much heat and a greater percentage of heat would exit the system as waste? At 3/4" max capacity or at 1/2 max capacity (in terms of wood burned/hr), a greater percentage of the heat from the burn could be stored by the system, but is the fire less efficient? At some point (imagine just burning one popsicle stick there's clearly not enough material to get the system hot enough to burn everything. So is there some magic point where the fire is hot enough to burn everything, but you're not pumping so much heat through your system that you can't catch it all? Os is the exact same percentage of heat being absorbed by the system regardless of the amount of wood burned/hr, and the heat of the exhaust is just a reflection of the heat that went into the system?

This is why I was wondering about the difference between a 6" and 8" system. Is a 6" system burning some amount of wood/hr exactly as efficient, not as efficient or more efficient than an 8" system burning the exact same amount of wood/hr? If the two systems are identical, than is the only advantage of an 8" system the amount of wood it can burn/hr and that some people either need a ton of heat, or only want to run their heater for a short amount of time and their system can receive a lot of heat quickly?

Thanks for any thoughts - Rick
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