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rocket mass heater optimal burn temperature

Posts: 5
Location: NH
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Erica, on one of your videos you mentioned that most RMHs burn between 400-700˚ on average. Is there an optimal temp to burn at? I mean if we constantly burn at the higher end of the range we probably get better combustion thus less ash, creosote, etc, but we waste higher temps going out the stack. But, if we burn on the lower end do we risk incomplete burns and end up with more ash and possibly creosote?
I hate to waste wood, but, I also hate to lose heat needlessly.
Posts: 1278
Location: Okanogan Highlands, Washington
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Good question Ray.

The burn temperature you mentioned is the temperature you see on the outside of the barrel, up near the top. That's your immediate radiant heat, like a woodstove. If you want it cooler / to store more heat, you can use a heat shield with air gap (converts some of the radiant heat to convective hot air heat), or you can put up some thermal mass (like our rock wall behind our barrel) and soak up some of the barrel heat that way.

The actual combustion temperature inside the RMH is probably between 1500 and 2600 F for most rocket mass heaters, cooling off slightly at the beginning and end of the burn cycle.

My target with RMH design is to hit 1100 F fairly quickly, but to stay below 2400 F if possible. This is kinda tricky given the variety of firewood and insulation options, but that's our goal.
Above 2400 F you do get very complete combustion, but you can start burning the nitrogen in the air, and that leads to NOx type pollution about 15 minutes downwind of your chimney.

Your rocket mass heater shouldn't have any problem capturing the heat from a nice, hot burn and storing it for overnight comfort. The surface temperatures of our bench get to about 80-95 F, very comfortable to sit on, and the whole house generally doesn't lose more than about 10 degrees over the following 24 hours. When we are gone for the day and don't light the stove, from 70 it may drop to 55 or 60 the following day when we get back.

Hope that helps!
Ray Dudley
Posts: 5
Location: NH
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Thank you so much Erica!
So, if I understand you, it's ok for my barrel to register 300-400˚ most of the time, with periodic spikes up to approx. 700˚, but, I don't need to constantly keep the barrel at the 700˚ point to get an efficient burn. Is that correct?
And it's ok to have long hours of burning at that 300-400 range?
My RMH (www.rmhnh.wordpress.com) bench is usually between 100-140˚. We LOVE our heater!
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Ray Dudley: In a semi perfect world, you brcome aware that your rocket has diminished in volume, you look down into your burn chamber and see some charcoal
and some burning embers basking in the reflected light from the red glowing walls of your Burn Tunnel/Combustion Chamber, and the next piece of wood that you
put in the feed tube seems to spontaneously bust into flames while you are reaching for the 2nd and third piece !

This is an ideal and only happens when you are truely working/living within a short arms length of your rocket stove and then just seems to happen automatically!

We say of training a young baby to potty training, first the parents get trained and then the child ! it is a lot like that with considerably less mess ! I hope this helps,
and is timely Big AL !
it's a teeny, tiny, wafer thin ad:
dry stack step
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