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My Rocket Mass Heater  RSS feed

 
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So it has taken about 2 years since the idea of one was mentioned to me. Ever since I have been researching and reading up all I can. I went out and got the rocket mass heater builders guide which let me tell you is the best. I have undergone so many trial and errors. Many revisions on where and how I wanted to do my heater. I first wanted to do 6 in then decided on 8 for a few reasons. My house is about 1400sq ft. two stories. I still have yet to put in cob but that is literally all that is left and it scares me the most. I have made many test bricks and found one that seems pretty tough so im just going to go with it. I know il get some words about having too many turns and elbows but its about 20ft+25ft worth of 90° angles. The chimney is about 25ft tall and with everything sealed it has a pretty great draft. Pulls paper down the tunnel pretty easily with no heat. Anyways I just thought id share some pictures before I cob everything since I have had a lot of help from you guys in this forum and it has been very much appreciated by me ☺
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Posts: 2581
Location: Upstate NY, zone 5
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Nice job! The only thing I would do differently, given the loops of duct format, is to make that jog with two 45 degree elbows instead of two 90s, for less flow restriction and easier cleaning reach. But if you have good strong draft, you should be fine. This system is on a concrete slab, right? What kind of insulation do you have under the ducts and core, to keep from heating the earth and possibly overheating the supporting structure?
 
Glenn Herbert
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Location: Upstate NY, zone 5
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Also, cobbing is easy (a lot of work, but not much you can really mess up.) Putting a lot of stones in the cob once you have covered the ducts will reduce the amount of cob you need to mix, and increase the heat storage capacity a bit as the stone will be denser. Just keep the stones back an inch or two from the exposed face unless you want to bring them all the way out to be exposed in the finished surface.
 
Kyler Lowrimore
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Yeah I was initially planning on taking out the last two 90° turns and making it less restrictive like you mentioned but after adding up all the turns and length it came to 45ft and from what I read a 8in can go 55ft. Plus every 10-15ft of chimney adds about 5ft of extra length I can add so I just figured keeping it at 45ft would give me optimal draft. I wanted to keep it somewhat restricting so the exhaust wouldn't just fly out the chimney too fast so it has more time to release the heat into my mass considering how short it is. Hopefully it works like I planned but only time will tell.

Under the mass I have about 2 1/2 inches of clay stabalized perlite and all around the riser about 3inches of it.

The only reason im worried about the cob is because my soil seems to be a bit silty. I did a soil test in a jar and it really showed no different layers like I was expecting. I did a few test bricks and found 1 soil to 1 sand and 1/4 of clay slip made the strongest bricks so I think it may work.
 
Kyler Lowrimore
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Oh and yes I got lucky and the house was built on a concrete slab! 😃
 
Kyler Lowrimore
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Also im assuming if it's drafting fine now without and actual fire that once I start burning it will only get stronger right?
 
Glenn Herbert
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I expect so. My RMH draws slightly when stone cold, and strongly with a fire in it.

If you use straw in your outer layers of cob, it should hold together well enough. I would put a substantial finish layer of lime plaster on it rather than attempting earthen plaster.
 
Kyler Lowrimore
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I really appriciate your advice Glenn, on all my posts you've been the one to help steer me in the right direction. I will probably put just a little hay in the middle and then use more in the outer layers and just wait until it dries and get it all plastered in with the lime in it! Hopefully after that il be good to go haha im putting a much larger version of this heater in my shop. I think either 10-12inch should be good
 
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Location: SW Missouri
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chicken hugelkultur solar
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That looks awesome. I think the location to the staircase looks great too. Good job.
 
Kyler Lowrimore
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Thank you! It looks a lot smaller in pictures but I plan to get a quote on taking out the staircase and putting up a spiral that will open up the downstairs area x10.
 
Oh, sure, you could do that. Or you could eat some pie. While reading this tiny ad:
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