Rocket Mass Heater for my home

Rocket Mass Heaters, Rocket Ovens, Cold boxes, Solar collectors, etc..
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Re: Rocket Mass Heater for my home

Postby matt walker » Wed Feb 15, 2012 2:10 am

Monday, I did a little shaping and final cutting on some of the cob I wasn't happy with, and had a visitor so we sat and talked stoves and enjoyed the heat. That brings us up to today, which I started by digging and mixing yet more cob. But not much, I'm almost there!

I dug out a rock I didn't like, and carved a relief in the face of the west bench to create a little nicer shape than what I had there.

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Then, I started the last cobbing session for a while. I dressed the faces and around the rocks, built some rests on the benches to keep cushions and people away from the barrel.

Then I mixed up and screened some plaster, and tried to get all the straw covered and deal with any real ugly spots. My goal was to get it to a point where I can leave it for a while and get on with some other projects. I think I'll be okay with this finish for now, until it dries more and I can work on thinner, brighter plaster to trap the dust and brighten it up. So, for now, here's what I have...

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Looks just like my original concept sketch, doesn't it? Hahahahaha. Don't ask me where this came from, but I'm okay with it for now. Plus, it's a great place to play with my star wars action figures. Kidding.


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Re: Rocket Mass Heater for my home

Postby matt walker » Wed Feb 15, 2012 2:20 am

I think I've come up with a couple innovations on this build, and I'm excited to share. I've not seen the window/door done in this way before, and I'm just so pleased with it. The ability to glance from across the room and see what the coals are doing is so helpful, and I can stare at the fire for hours. It's really neat the way it spirals in the burn tunnel and then shoots up the riser. Entrancing.

The window/door led to that extra tunnel, or wing as Guy calls it. That wing makes an excellent oven, and I will include this feature in any future builds and hopefully increase the size of this one. I bake all the time, and the flavor of the bread in the wood fired oven is to die for. I'm exceptionally pleased with this discovery, it's just wonderful.

Adding the cast iron surface above the oven. My original thought was a place to set my coffee in the morning, a little warming pad. It is just right for that when the fire is starting and uncovered, but I can stuff the fire box and cover it and get this hot enough to hold a low simmer.

Overall, so far, I'm just flat out blown away by the quality of life improvement this stove is already offering me. No more fighting to start a fire, and waiting for the heat. No more coming home after work to the house cold, and working my butt off to warm it up again. I could go on and on, but I'll just say that last night it was 38* out, and i had the front door wide open for around 45 minutes because the house was so dang hot. Granted, I'm burning it hot to dry everything out, but the fact that it can do that is just wonderful. My big box stove would have had to be running full tilt for hours to try to pull that off.
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Re: Rocket Mass Heater for my home

Postby Lollykoko » Wed Feb 15, 2012 2:47 am

I was day dreaming somewhere in the thread. The oven is where? In the right hand (looking at the heater) bench behind a rock door?

It looks great so far, Matt. This thread will make Sis so much more agreeable to the idea of having a few of these heaters built in various rooms.
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Re: Rocket Mass Heater for my home

Postby matt walker » Wed Feb 15, 2012 2:59 am

Well, I didn't know I had an oven either! No, it's the "viewing tunnel" or whatever, right behind the door/window in the center. That tunnel is almost a foot long before it intersects the feed tube, so I just stick my bread in there. Works great!
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Re: Rocket Mass Heater for my home

Postby Lollykoko » Wed Feb 15, 2012 3:08 am

Aha! That's even better, since you can see whether the loaf is browned or the cheese has melted on your onion soup.
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Re: Rocket Mass Heater for my home

Postby George Collins » Wed Feb 15, 2012 3:57 am

Matt, that thing looks really cool. Almost makes me wish I lived in some place cold so I could try my hand at building one.
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Re: Rocket Mass Heater for my home

Postby pa_friendly_guy » Wed Feb 15, 2012 3:58 pm

The heater looks great Matt. I see that it is starting to dry out some. You can see in the pictures the different colors in the cobb from wet to dry. How long do you expect it to take to dry completely? Have you seen any cracking in the cobb so far? I would not think small cracks would cause you any problems. The viewing door that has turned into an oven was a Great idea. I have never seen one befor either, I like the inovation. Do you turn the loaf 1/2 way through to get it to bake evenly on both sides? Great job all around, now for the $64000 question, how does it heat your house? Do you feel that it uses alot less wood than the old metal wood stove? Does it keep you warmer in the mornings when you get up than the old stove did? How does the heat travel through the house, is it as even a heat as the old stove. Bottom line, are you staying warmer and using less wood like you figured you would. Or if you are useing about the same amount of wood, is your comfort level higher and is the house warmer. Does the large mass really hold and radiate the heat for hours like they say it would? Does it work as advertized, lol, I am not a betting man by nature, but I would bet that it does.
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Re: Rocket Mass Heater for my home

Postby matt walker » Wed Feb 15, 2012 5:46 pm

As for cracking, nothing major, but the material does have small cracks here and there. Nothing that concerns me at all, and once it dries I'll apply more plaster and smooth things out. It is WET. That's one thing I didn't read about anywhere, but was sort of expecting. The house is really humid right now, and I expect it will be weeks or more before the bench is fully dry. Because I'm actively trying to dry it, I'm burning it more than I will in normal use.

As for heat and wood use, it's too early to tell, but so far so good. I'm trying to burn constantly to dry it, and even so I'm using around half of the wood I was before, and having to keep a window or the door open because it gets so warm in here. I think I'm losing a lot of energy to evaporation as well, so the mass is cooling faster, but even so I'm waking up to a warm house. I'll keep posting on performance as I progress, but so far I'm very pleased.
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Re: Rocket Mass Heater for my home

Postby dave brenneman » Fri Feb 17, 2012 10:22 pm

matt, that is gorgeous. the oven in the front is a great thing, too!
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Re: Rocket Mass Heater for my home

Postby matt walker » Thu Feb 23, 2012 1:58 am

Okay, update time! It's been slow around the board lately, and I apologize for not spending more time. I've been playing catch up since I dedicated so much time to my stove, and on top of that, I just want to sit on the warm bench and stare at the fire. My computer time is WAY DOWN! I think we can add that as another feature in the positive column for the RMH.

Anyway, it's becoming quite dry, no more moisture on the windows in the morning, although I'm sure it's still quite wet inside. So, for quality of heat in the house, A+. I can quickly heat the house to too warm with a relatively small amount of wood, and easily surpass the old box stove's output. I can get it to 80*F in here with outside temps in the high 30*'s. The box stove just couldn't do that, not that I experienced, anyway.

The bench is amazing, sitting on that thing is heaven. I've taken to watching movies from there, and it's like a hot tub. I'm just melted after a few hours on it.

The stove is holding up well, the clay in the feed is kinda taking a beating, but not noticeably deteriorating at any alarming rate. I have reshaped the mouth of the feed with more clay and perlite a couple times. Most recently was yesterday, I choked it down a bit, and the stove is running flawlessly. I now get absolutely not a touch of smoke, or flame creep, or any associated annoyances. I had been having a bit of trouble since my wood is all 18" or so long, and wet. The wood wouldn't drop because the core was wet, before the outsides burned high enough to smoke. I was covering the load often, which worked fine. However, by restricting the inlet, even with long wood, the downdraft is strong enough to keep everything in the feed. I'm very pleased.

Splitting the wood is kind of a pain in the ass, honestly. I am operating under the assumption that this is a temporary situation due to having wood for my old stove, which all needs splitting down to 2" or so pieces to use in the RMH. I believe that next season I will be stocking up on coppiced Maple and Alder and will no longer have to split wood ever, so I am accepting this season's chore of whittling the big wood down to little wood.

It's colder in the mornings than it was with the box stove. Not bad, and I accept it and realize overall it is an improvement, but I'm trying to be honest about the pros and cons. I am waking up to the house about 64* on average, with outside temps just above freezing. Frankly, that's fine with me, but the box stove, set to smolder all night, would have the house around 68* in the am. The difference is if the box stove went out, the house temp would plummet, while the RMH hasn't let it go below 60*, even when it was out for 20 hours the other day. It also picks up the temp MUCH faster, so I'm overall pleased. However, there really isn't an option other than 64* in the morning. It's not like I can stuff more wood in it before I go to bed.

Air quality in the house is greatly improved. People talk a bit about smoke back with the RMH. Let me tell you, one episode of struggling to get the box stove going with a wet load, or fired up from smoldering all night, put WAY more smoke in the house than the RMH has total. I'm sure of that. In addition, the layer of fine ash dust that the box stove put over everything in the house, and the smell of wood smoke, is gone. The RMH keeps the air circulating and doesn't allow any ash out at all. I love this feature.

I dissembled the last few sections of flue yesterday, and they are as clean as can be. I think I've effectively eliminated chimney cleaning/maintenance for the foreseeable future. I'm really stoked on that.

I've discovered that the wood I want, most people consider trash. I've picked up a bale, which my 3/4 ton diesel truck could barely hold, of kiln dried offcuts from a local manufacturing facility, for free. They have bales and bales laying outside their facility, free for the taking. No body wants them. I've burned the stove for three days on a wheelbarrow full, which didn't even make a visible dent in my truck load. Yay!!!!

There's more, but I'll stop fawning for now. I wish I had put this thing in years ago.
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